Applied Catalysis A, General (v.407, #1-2)
Editorial Board (CO2).
A review of catalytic upgrading of bio-oil to engine fuels by P.M. Mortensen; J.-D. Grunwaldt; P.A. Jensen; K.G. Knudsen; A.D. Jensen (1-19).
Display Omitted► Biofuel production on the basis of bio-oil. ► Upgrading of bio-oil through HDO or zeolite cracking to crude oil-like products. ► Pronounced catalyst deactivation due to carbon deposition. ► HDO appears to have the better potential for biofuel production of the two routes.As the oil reserves are depleting the need of an alternative fuel source is becoming increasingly apparent. One prospective method for producing fuels in the future is conversion of biomass into bio-oil and then upgrading the bio-oil over a catalyst, this method is the focus of this review article. Bio-oil production can be facilitated through flash pyrolysis, which has been identified as one of the most feasible routes. The bio-oil has a high oxygen content and therefore low stability over time and a low heating value. Upgrading is desirable to remove the oxygen and in this way make it resemble crude oil. Two general routes for bio-oil upgrading have been considered: hydrodeoxygenation (HDO) and zeolite cracking. HDO is a high pressure operation where hydrogen is used to exclude oxygen from the bio-oil, giving a high grade oil product equivalent to crude oil. Catalysts for the reaction are traditional hydrodesulphurization (HDS) catalysts, such as Co–MoS2/Al2O3, or metal catalysts, as for example Pd/C. However, catalyst lifetimes of much more than 200 h have not been achieved with any current catalyst due to carbon deposition. Zeolite cracking is an alternative path, where zeolites, e.g. HZSM-5, are used as catalysts for the deoxygenation reaction. In these systems hydrogen is not a requirement, so operation is performed at atmospheric pressure. However, extensive carbon deposition results in very short catalyst lifetimes. Furthermore a general restriction in the hydrogen content of the bio-oil results in a low H/C ratio of the oil product as no additional hydrogen is supplied. Overall, oil from zeolite cracking is of a low grade, with heating values approximately 25% lower than that of crude oil. Of the two mentioned routes, HDO appears to have the best potential, as zeolite cracking cannot produce fuels of acceptable grade for the current infrastructure. HDO is evaluated as being a path to fuels in a grade and at a price equivalent to present fossil fuels, but several tasks still have to be addressed within this process. Catalyst development, understanding of the carbon forming mechanisms, understanding of the kinetics, elucidation of sulphur as a source of deactivation, evaluation of the requirement for high pressure, and sustainable sources for hydrogen are all areas which have to be elucidated before commercialisation of the process.
Keywords: Bio-oil; Biocrudeoil; Biofuels; Catalyst; HDO; Hydrodeoxygenation; Pyrolysis oil; Synthetic fuels; Zeolite cracking;
Study in support effect of In2O3/MO x (M = Al, Si, Zr) catalysts for dehydrogenation of propane in the presence of CO2 by Miao Chen; Jia-Ling Wu; Yong-Mei Liu; Yong Cao; Li Guo; He-Yong He; Kang-Nian Fan (20-28).
Display Omitted► Support effect of the In2O3/MO x (M = Al, Zr, Si) is studied. ► Dehydrogenation of propane with CO2. ► Yield of propylene: In2O3/Al2O3 > In2O3/ZrO2 > In2O3/SiO2. ► Promotion effect via reverse water-gas shift was the most remarkable for In2O3/ZrO2. ► Well dispersion of indium-species and balanced acid–base properties is important.Two series of binary In2O3/MO x (M = Al, Zr, Si) catalysts with low (3 wt%) and high (10 wt%) In2O3 loadings were prepared via an incipient wetness impregnation method. The support effect has been investigated in detail by testing the propane dehydrogenation (PDH) reaction both in the presence and absence of CO2. Physico-chemical properties including surface composition, redox and acidic/basic properties of the supported In2O3 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, NH3 and CO2 temperature-programmed desorption, respectively. It was demonstrated that a higher population of the specific highly dispersed In2O3 species on support is favorable for propylene production, and the maximum propylene yield was achieved with the high-loading In2O3/Al2O3. Properties including high In2O3 dispersion and balanced acidic/basic properties, rendering synergism between dehydrogenation and reverse water gas shift, are essential for achieving high catalytic performance of PDH.
Keywords: Indium oxide; Dehydrogenation; Propane; Carbon dioxide; Support effect;
A new approach in the evaluation of the support effect for NiMo hydrodesulfurization catalysts by T.K.T. Ninh; L. Massin; D. Laurenti; M. Vrinat (29-39).
Display Omitted► Comparison of MoS2 and NiMoS catalysts onto alumina, silice, titania and zirconia. ► Ni-promotion of MoS2-supported catalysts by using Ni(acac)2. ► XPS quantification of NiMoS phase onto different supports. ► Intrinsic catalytic HDS activities of NiMoS active sites.To evaluate the intrinsic effect of some supports (γ-Al2O3, SiO2, TiO2, ZrO2) on the activity of hydrodesulfurization (HDS) catalysts, NiMo catalysts were prepared by adding nickel acetylacetonate (Ni(acac)2) to supported molybdenum sulfide. The catalysts were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy and then tested in HDS of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT). This preparation method allowed obtaining well-promoted catalysts. A higher percentage (69–80%) of NiMoS phase was observed by XPS for these catalysts than for traditional co-impregnated catalysts (60%). In addition, the catalytic activity measured with those promoted systems was improved especially for TiO2 and ZrO2 supported NiMoS catalysts. By combining characterizations, geometrical model and catalytic activities, apparent HDS activities per NiMoS site were evaluated on each support. The high quality of NiMoS sites suggests that Type-II sites have been formed on silica.
Keywords: Preparation; NiMo supported catalysts; Hydrodesulfurization; Support effect; Ni(acac)2; XPS;
Synthesis and characterization of new solid acid catalysts, H3PW12O40 supported on nanoparticle tin oxide: An efficient catalyst for the preparation of 7-hydroxy-4-methylcoumarin by Awad I. Ahmed; S.A. El-Hakam; M.A. Abd Elghany; W.S. Abo El-Yazeed (40-48).
Display Omitted► We prepare TPA/SnO2 by impregnating SnO2 with the appropriate amount of TPA solution to obtain 3, 7, 10, 15, 25 and 30 wt% TPA. ► We conclude that the surface area values increase gradually with increasing TPA loading. ► We observe that 30 wt% TPA/SnO2 calcined at different temperatures contains the strongest and the highest number of acid sites. ► We use the catalysts for the preparation of 7-hydroxy-4-methylcoumarin. ► We conclude that the formation of 7-hydroxy-4-methylcoumarin increases gradually with increasing the amount of TPA loaded on SnO2.A series of 12-tungstophosphoric acid (TPA) modified SnO2 samples (TPA–SnO2) with varying TPA content were prepared by wet impregnation technique. The TPA–SnO2 catalysts were characterized by thermal analysis, powder X-ray diffraction (XRD) patterns and N2 adsorption at −196 °C. The surface acidity was measured by potentiometric titration and FTIR spectra of chemically adsorbed pyridine. The DTA shows a peak maximum at 600 °C which was ascribed to the crystallization of tin oxyhydroxide into SnO2. The thermograms of TPA show no exothermic effect due to the decomposition of TPA up to 25 wt%. When TPA content reached 30 wt% TPA/SnO2 an exothermic effect at 618 °C indicated that the thermal stability of TPA on SnO2 seems to be comparable to that of pure TPA. XRD measurements showed that there are no diffraction patterns of TPA for the catalyst calcined at 500 °C. The presence of TPA on tin oxide inhibits sintering of the particles during calcination by reducing the crystallite size of SnO2 from 27.7 to 19.8 nm. The surface area values increase gradually with increasing TPA loading to reach a maximum limit of 25 wt% TPA. When calcination temperature is increased to 500 °C the specific surface is decreased. The acidity measurements showed that the total acidity increases with the rise of TPA content up to 30 wt%. FTIR spectra of pyridine adsorbed on the catalysts showed the presence of both Bronsted and Lewis acid sites. An optimum reaction performance (78.0% of 7-hydroxy-4-methyl coumarin formed) was achieved at 30 wt% loading of TPA calcined at 400 °C and reaction conditions of 120 °C, 2 h reaction and 1:2 (resorcinol:ethyl acetoacetate) molar ratio.
Keywords: 12-Tungstophosphoric acid; Tin oxide; Calcination temperature; Surface acidity; Resorcinol; Ethyl acetoacetate; Coumarin;
Influence of gallium on the properties of Pt–Re/Al2O3 naphtha reforming catalysts by María A. Vicerich; Catherine Especel; Viviana M. Benitez; Florence Epron; Carlos L. Pieck (49-55).
Display Omitted► The influence of Ga addition on the properties and performance of Pt–Re/Al2O3 catalysts for naphtha reforming was studied. ► The incorporation of Ga decreases both acidity (Brønsted and Lewis) and metal functions (dehydrogenation and hydrogenolysis). ► Catalyst stability and selectivity to aromatics were improved, and a lower production of light was observed upon Ga addition.The influence of gallium on the properties of Pt–Re/Al2O3 catalysts used in naphtha reforming was studied. The catalysts were prepared by the coimpregnation method. It was found that the addition of gallium to the Pt–Re/Al2O3 catalyst diminishes its acidity (Brønsted and Lewis). It also produces an inhibition of the metal function, i.e. dehydrogenation and hydrogenolysis activity. Activity tests for n-C5 isomerization showed that gallium addition decreases the total activity of the Pt–Re catalyst but increases its selectivity to i-C5 isomers. The selectivity to low value light gases (C1–C3) is particularly decreased. Catalytic tests for n-C7 reforming showed that addition of gallium increases both catalyst stability and selectivity to aromatics, and decreases the production of light gases.
Keywords: Naphtha reforming; Pt–Re–Ga/Al2O3 catalysts;
Hydrotreatment of wood-based pyrolysis oil using zirconia-supported mono- and bimetallic (Pt, Pd, Rh) catalysts by A.R. Ardiyanti; A. Gutierrez; M.L. Honkela; A.O.I. Krause; H.J. Heeres (56-66).
Display Omitted► Noble metal catalysts on ZrO2 were tested for hydrotreatment of pyrolysis oil. ► The catalysts are more active on a metal basis than the benchmark CoMo/Al2O3. ► Rh/ZrO2 gave a product oil with the lowest tendency for coking (TG residue). ► A reaction network is proposed and involves repolymerisation and hydrogenation. ► Carbonaceous deposits on spent catalysts can be removed by an oxidation step.Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 °C, 20 MPa total pressure, and 4 h reaction time) with mono- and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO2 showed the highest activity, followed by Rh/ZrO2. Upgraded oils with the best product properties were obtained with Rh/ZrO2. For this catalyst, the TGA residue, which is a measure for coking tendency, was 13.4 wt% and the M w of the upgraded oil (748 g/mol) was lowest. All noble metal catalysts showed higher activities per gram of metal than the benchmark catalyst CoMo/Al2O3. Hydrotreatment reactions at variable batch times were performed to gain insights in reaction pathways and showed the involvement of competitive hydrogenation/hydrocracking and polymerisation pathways. Temperature programmed oxidation (TPO) measurements of spent catalysts showed the presence of carbonaceous deposits on the catalyst (2–6 wt%). These deposits may be removed by oxidation at temperatures lower than 600 °C without changing the morphology of the catalyst.
Keywords: Wood-based pyrolysis oil; Hydrogenation; Hydrotreatment; Noble metal catalysts;
Abatement of nitrous oxide over natural and iron modified natural zeolites by Ayten Ates; Andreas Reitzmann; Christopher Hardacre; Huseyin Yalcin (67-75).
Display Omitted► The iron modified natural zeolites show high activity in the reduction of N2O. ► The natural zeolites prepared with FeCl2 have more reducible iron species. ► Iron loading, precursor and valency affect the catalytic performance of catalysts. ► Sulphate remained on the surface causes a decrease in the N2O decomposition activity.The natural zeolite obtained from the Sivas-Yavu region in Turkey and iron modified forms were studied for the decomposition of N2O and selective catalytic reduction of N2O with NH3. The natural and iron modified zeolites were characterised by XRD, SEM, H2-TPR, NH3-TPD and low temperature nitrogen sorption. The effect iron loading, precursor and valency on the catalytic performance of catalysts were studied. The catalytic activity of the zeolites increased up to about 7.0 wt.% Fe. Above this value, the activity decreased as a result of a reduction in the surface area and pore volume of the zeolite. The highest catalytic activity was observed using catalysts prepared with FeCl2 due to the formation of more reducible iron species in the zeolites. When FeSO4 was used as the iron precursor, sulphate remained on the surface even after extensive washing resulting in a decrease in the N2O decomposition activity and a shift the N2O reduction temperature to higher values. Since the natural and iron exchanged natural zeolites prepared using FeCl2 have comparable activity with synthetic zeolites, the offer a promising alternative catalyst for the abatement of N2O, particularly for the selective reduction of N2O with NH3.
Keywords: Decomposition; Selective catalytic reduction; Nitrous oxide; Natural zeolite; Ammonia;
Selective oxidation of ethylbenzene over CeAlPO-5 by Subbiah Devika; Muthiahpillai Palanichamy; Velayutham Murugesan (76-84).
Display Omitted► A novel route for the synthesis of CeAlPO-5 catalysts is devised. ► High activity of ethylbenzene oxidation and high selectivity to acetophenone are reported. ► A new mechanism is suggested for selective oxidation. ► The oxidation process can be applied to industries.CeAlPO-5(Al/Ce = 25, 50, 75, 100 and 125) molecular sieves were synthesized hydrothermally in fluoride medium and their structures were confirmed from an XRD analysis. The incorporation of Ce3+ into the framework was verified by XRD and DRS-UV–Vis analyses. The surface areas were in the range of 202–215 m2 g−1. The ESR spectrum revealed the presence of adsorbed oxygen which was evident from the peak at g = 2.0. The catalytic activity of molecular sieves was tested in the vapour phase oxidation of ethylbenzene between 150 and 250 °C. CeAlPO-5(25) showed higher conversion than other catalysts. The selectivity to acetophenone was above 90% at all the temperatures. The selective oxidation of methylene group was ascribed to slow rotation of the ethyl group compared to its methyl group at the reaction temperature. Cerium was not leached out in CeAlPO-5(25) even after activation of the spent catalyst at 550 °C. The time on stream study also indicated the absence of catalyst deactivation.
Keywords: CeAlPO-5; Hydrothermal synthesis; Fluoride medium; Ethylbenzene; Oxidation; Acetophenone;
Codimerisation of styrene and α-methylstyrene in the presence of zeolites by N.G. Grigor’eva; S.V. Bubennov; L.M. Khalilov; B.I. Kutepov (85-90).
Display Omitted► Codimerisation of styrene and α-methylstyrene. ► Zeolites HY, HBeta and HZSM-12. ► Linear and cyclic homo- and codimers of styrene and α-methylstyrene. ► Conversion styrene and α-methylstyrene. ► Zeolite ZSM-12 promote the synthesis of linear compounds.The reaction of styrene with α-methylstyrene has been studied over Y, Beta and ZSM-12 zeolites at 80–120 °C in the presence or absence of chlorobenzene. Homo- and codimers of styrene and α-methylstyrene were the main reaction products. The yield of dimers and their structure depends on zeolite type and the experimental conditions. Dimers were formed with greater selectively over zeolite HZSM-12 (S = 80–83%), for which the structural features promote the synthesis of linear compounds. In the presence of the zeolites HY and HBeta, cyclic homo- and codimers were the predominant products. The yield of dimers increases with increased reaction temperature and catalyst concentration, and in the presence of solvent. All zeolites investigated showed high codimerisation activity on styrene and α-methylstyrene at 120 °C.
Keywords: Codimerisation; Styrene; α-Methylstyrene; Homo-dimers; Codimers; Zeolites;
Hydrogen spillover behavior of Zn/HZSM-5 showing catalytically active protonic acid sites in the isomerization of n-pentane by Sugeng Triwahyono; Aishah Abdul Jalil; Rino R. Mukti; Malik Musthofa; N. Aini M. Razali; M. Arif A. Aziz (91-99).
Display Omitted► Zn2+ exchanged the Brønsted acid sites to Lewis acid sites. ► Active protonic acid sites are formed from H2 via hydrogen spillover mechanism. ► Lewis acid sites and Zn species are indispensable in the formation of H+. ► The catalytic activity of Zn/HZSM-5 is strongly determined by the presence of H+. ► Low activity was observed on Zn-free HZSM-5 under H2 carrier gas.The impregnation of zinc particles into MFI zeolite (HZSM-5) caused the formation of catalytically active protonic acid sites for isomerizing n-pentane in the presence of hydrogen. An infrared (IR) study with preadsorbed pyridine revealed that these protonic acid sites originated from the spillover of molecular hydrogen from the zinc species onto the zeolite surface. The requirements for this spillover effect were further studied by IR spectroscopy of adsorbed ammonia and carbon monoxide. The presence of zinc species in HZSM-5 suggested the exchange of acidic character towards strong Lewis acids rather than Brønsted acid sites. The isomerization of n-pentane over the Zn/HZSM-5 catalyst resulted in high activity and stability and the conversion to iso-pentane depends on the promotive effect of hydrogen as a carrier gas.
Keywords: Zn/HZSM-5; Protonic acid sites; Lewis acid sites; Molecular hydrogen; n-Pentane isomerization;
Composite ferrite catalyst for ethylbenzene dehydrogenation: Enhancement of potassium stability and catalytic performance by phase selective doping by Andrzej Kotarba; Weronika Bieniasz; Piotr Kuśtrowski; Katarzyna Stadnicka; Zbigniew Sojka (100-105).
Display Omitted► Functional morphological model of a robust ferrite EBDH catalyst was developed. ► Selective doping of K2Fe22O34 with Ce, Cr is essential for stable active and selective K-Fe-O catalyst. ► Surface ferrites equilibrium revealed from UHV studies was realized in practice.Composite ferrite catalyst consisting of pristine irregular KFeO2 crystallites and well developed hexagonal nanoplates of selectively doped (2%Ce,2%Cr)-K2Fe22O34 was prepared, characterized (XRD, HR-TEM, SEM-EDX, BET) and tested for potassium volatilization and catalytic performance in ethylbenzene dehydrogenation. In comparison with separate parent ferrite phases the obtained composite catalyst exhibited superior overall catalytic performance (stability and activity), combining the best features of its components. Indeed, it exhibits the conversion and selectivity to styrene monomer of the most active phase of 2% Ce, 2% Cr-doped K2Fe22O34, whereas the thermal stability of potassium was even higher than in the most stable KFeO2 phase.
Keywords: Styrene catalyst; Potassium ferrites; Potassium loss; KFeO2; K2Fe22O34; Stability; Iron oxide; Ethylbenzene dehydrogenation; EBDH;
Ab-initio study of effect of basic MgO to V2O5 catalyst on oxidative dehydrogenation of C3H8 and n-C4H10 by Nguyen Ngoc Ha; Ngo Duc Huyen; Le Minh Cam (106-111).
Display Omitted► The first theoretical study of the effect of basic MgO to V2O5 catalyst on oxidative dehydrogenation of C3H8 and n-C4H10. ► The reason why to avoid creating Mg3(VO4)2 when preparing the catalyst for ODH of n-C4H10. ► Successful use of electron density, spin density, XANES to explain the cause of the difference in catalytic activity when added MgO to V2O5.Ab-initio study using the density-functional theory (DFT) method to investigate the role of MgO, a basic material to oxidative dehydrogenation of C3H8 and n-C4H10 using V2O5 catalyst. The detailed calculations suggest that V2O5/MgO instead of compound Mg3(VO4)2 can be used for ODH of both alkanes but V2O5 supported on MgO may not be the most suitable catalyst for the ODH of n-C4H10. And when preparing the catalyst for ODH of n-C4H10 it should be avoided creating Mg3(VO4)2, a low catalytic activity.
Keywords: ODH; DFT; Activation of C–H bond;
Screening of new additives to heteropoly acid catalyst for Friedel–Crafts reaction by microwave heated HTS and by Gaussian process regression by Kohji Omata (112-117).
Display Omitted► Catalyst screening was accelerated by microwave-HTS and Gaussian process regression (GPR). ► Regression model by GPR was superior to those by radial basis function network and support vector machine. ► Pt-HPA (heteropoly acid) showed 8 times higher activity than that of HPA for benzylation of anisole at 130 °C.Activity of heteropoly acid (HPA) catalyst for Friedel–Crafts reaction was promoted by Pt addition of which effect was discovered by means of microwave heated high-throughput screening (HTS) and Gaussian process regression (GPR). In the screening, activities of Na, Mg, Mn, Zn, Pd, Cs, Pr and W promoted HPA were measured, and every activity test using microwave irradiation required only 150 s. The results and physicochemical properties of these 8 elements were used to construct regression models by a radial basis function network (RBFN), a support vector machine, and GPR. The regression model by GPR predicted that Pt is an effective additive, which promotes the activity, and the activity was experimentally verified to be 8 times higher than that of the unpromoted HPA catalyst. The performance of the regression model by GPR was superior to those by RBFN or by SVM because an excellent effect of Pt addition was discovered only by GPR. In addition to the extrapolative prediction, advantages of GPR model are that the performance and accuracy of the regression model are increased by using expected improvement which can suggest the additional experiments necessary for the improvement of the regression model.
Keywords: Friedel–Crafts reaction; High-throughput screening; Microwave heating; Principal component analysis; Nonlinear regression; Gaussian process regression;
Catalytic mechanism of the dehydrogenation of ethylbenzene over Fe–Co/Mg(Al)O derived from hydrotalcites by Balkrishna B. Tope; Rabindran J. Balasamy; Alam Khurshid; Luqman A. Atanda; Hidenori Yahiro; Tetsuya Shishido; Katsuomi Takehira; Sulaiman S. Al-Khattaf (118-126).
Display Omitted► Fe3+–Co3+/2+(1/1) active species by Fe3+/Fe2+ reduction–oxidation accelerated by Co3+/2+. ► Important role of Fe3+ as Lewis acid sites as well as Mg2+–O2− as base sites on the catalyst. ► Formation of C–O bonding as the reaction intermediate on the catalyst. ► α-H+ abstraction on Mg2+O2− base sites, followed by C–O–Mg bond formation and β-H+ abstraction.Catalytic mechanism of ethylbenzene dehydrogenation over Fe–Co/Mg(Al)O derived from hydrotalcites has been studied based on the XAFS and XPS catalyst characterization and the FTIR measurements of adsorbed species. Fe–Co/Mg(Al)O showed synergy, whereas Fe–Ni/Mg(Al)O showed no synergy, in the dehydrogenation of ethylbenzene. Ni species were stably incorporated as Ni2+ in the regular sites in periclase and spinel structure in the Fe–Ni/Mg(Al)O. Contrarily, Co species exists as a mixture of Co3+/Co2+ in the Fe–Co/Mg(Al)O and was partially isolated from the regular sites in the structures with increasing the Co content. Co addition enhanced Lewis acidity of Fe3+ active sites by forming Fe3+–O–Co3+/2+(1/1) bond, resulting in an increase in the activity. FTIR of ethylbenzene adsorbed on the Fe–Co/Mg(Al)O clearly showed formations of C–O bond and π-adsorbed aromatic ring. This suggests that ethylbenzene was strongly adsorbed on the Fe3+ acid sites via π-bonding and the dehydrogenation was initiated by α-H+ abstraction from ethyl group on Mg2+–O2− basic sites, followed by C–O–Mg bond formation. The α-H+ abstraction by O2−(–Mg2+) was likely followed by β-H abstraction, leading to the formations of styrene and H2. Such catalytic mechanism by the Fe3+ acid–O2−(–Mg2+) base couple and the Fe3+/Fe2+ reduction–oxidation cycle was further assisted by Co3+/Co2+, leading to a good catalytic activity for the dehydrogenation of ethylbenzene.
Keywords: Ethylbenzene dehydrogenation; Styrene; Fe3+–O–Co3+/2+(1/1) active species; Hydrotalcite; EXAFS; FTIR; C–O bond formation;
Ca2+-exchanged ferrierite: Quasi one-dimensional zeolite for highly selective and stable formation of light alkenes in catalytic cracking of n-octane by Lixia Wang; Kenichi Ozawa; Takayuki Komatsu; Takuji Ikeda (127-133).
Display Omitted► In Ca2+-exchanged ferrierite, exchanged cations block 8-MR channels and make ferrierite quasi one-dimensional. ► Ca2+-exchange into ferrierite reduces the bimolecular hydride transfer to increase the selectivity to light alkenes greatly. ► Ca2+-exchange into ferrierite suppresses the coke formation to improve its stability greatly. ► Ca2+-exchange into ferrierite decreases the acid density and acid strength.The catalytic cracking of n-octane was carried out as a model reaction of naphtha cracking to produce light alkenes on proton-form zeolites of various pore dimensions such as ZSM-5, ferrierite, ZSM-12, ZSM-22, SAPO-11 and SAPO-31. Among them, ferrierite is of good activity. However, the selectivity to light alkenes and the stability of conversion were not satisfactory. After ion exchange with Ca2+ ions, a great improvement has been obtained both in the selectivity to light alkenes and the stability of conversion. TG analysis showed that the amount of coke formed decreased with the increase in the Ca2+-exchange level. Structure analysis using powder XRD data revealed that Ca2+ ions are located at the center of 8-MR channels near the intersection of 8-MR and 10-MR channels (Ca1) and in the wall between 5-MR pores and 8-MR channels (Ca2). Ca2+ ions in Ca1 sites reduce the dimension of ferrierite pores partly to form quasi one-dimensional pore structure. This change in pore dimension would reduce the hydride transfer to consume initially formed alkenes and to form coke precursors. NH3-TPD showed that the ion exchange with Ca2+ reduced the acid density and the amount of strong acid sites; these changes in acidity can also reduce the hydride transfer.
Keywords: Ferrierite; Zeolite; Octane cracking; Ion exchange; Light alkene;
AgNaMordenite catalysts for hydrocarbon adsorption and deNO x processes by Soledad G. Aspromonte; Ramiro M. Serra; Eduardo E. Miró; Alicia V. Boix (134-144).
Display Omitted► The Ag+ ions improve the toluene adsorption and retention at high temperature. ► Ag has two opposite effects: obstruction of the pores and interaction with hydrocarbon. ► The AgMOR are active in the SCR-NO x with C7H8 or C4H10, excess O2 and 2% H2O. ► H2 and coke formation due to the interaction between C7H8 and Ag+ was observed.Silver catalysts were prepared by ion exchange of NaMordenite with 5, 10 and 15 wt% Ag. Various characterization techniques such as TPR, UV–vis and XPS indicated the presence of small particles of highly dispersed Ag2O together with isolated Ag+ cations located in α, β and γ exchange sites of NaMOR. The formation of clusters of cationic silver (Ag n m+) was also considered.The prepared samples were active in the Selective Catalytic Reduction of NO x in the presence of toluene or butane as reducing agents, excess oxygen and 2% H2O. The solid with 15 wt% Ag was the most active one in the presence of water, reaching a maximum conversion of NO x to N2 of 47.5% or 51.2% when butane or toluene were respectively used. Under dry conditions, the maximum conversion of NO had an optimum between 5 and 10 wt% Ag for both hydrocarbons.The NaMOR support showed a higher adsorption capacity than the exchanged samples with both hydrocarbons. For the silver loaded solids, the toluene adsorption capacity at 100 °C increased with the increase of the metal content. In contrast, the amount of butane adsorbed was similar for the different contents of Ag. Consequently, silver has two opposite effects: one is the partial obstruction of the mordenite channels, as seen by the loss of crystallinity and the decrease of surface area and pore volume; and the other effect is the chemical interaction that depends on the nature of the adsorbed hydrocarbon. The interaction between toluene and Ag+ ions is stronger with the π-electrons of the aromatic ring of the toluene molecule than with the σ-electrons of the linear chain of butane. For this reason, toluene is retained at higher temperatures than butane. In addition, between 300 and 500 °C, the appearance of signals corresponding to H2, CO2 and H2O is observed during the TPD of toluene. This indicates that the toluene decomposition occurs, producing coke and hydrogen. Most probably, the generation of CO2 and H2O is a consequence of the reduction of Ag2O particles with toluene.
Keywords: Toluene adsorption; Butane adsorption; SCR-NO x ; AgNaMordenite;
Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al2O3: I. Catalytic stability, electronic properties and coking mechanism by Catherine K.S. Choong; Ziyi Zhong; Lin Huang; Zhan Wang; Thiam Peng Ang; Armando Borgna; Jianyi Lin; Liang Hong; Luwei Chen (145-154).
Display Omitted► Effect of Ca on Ni/Al2O3 for low temperature ethanol steam reforming (ESR). ► Ca affects Ni particle size, electronic properties and steam gasification of coke. ► Optimal Ca loading is essential for the stability of catalyst in ESR.Ca-modified Ni/Al2O3 catalysts with various Ca loadings of 0, 3, 5 and 7 wt% were studied for low temperature catalytic ethanol steam reforming (ESR). Catalyst with 3 wt% of Ca remains stable at 673 K for at least 24 h, while 0 wt%, 5 wt% and 7 wt% Ca modified catalysts deactivate easily. The addition of Ca increases the particle size of active Ni which promotes the formation of un-reactive and encapsulating carbons, undermining the stability of highly loaded (7 wt%) Ca-modified Ni catalyst. XPS valence band shows that the presence of Ca increases the density of Ni 3d band valence electrons which helps in dissociation of methane and deactivates the catalysts, as in the case of nickel catalysts supported on 7 wt% of Ca on Al2O3. Excellent catalytic performance of 10Ni/3Ca-Al2O3 is due to the effective coke removal and the amorphous nature of coke deposition. Optimized Ca loading was found to play a critical role in coke removal, through its effect on Ni particle size, valence band of catalyst and steam gasification of coke.
Keywords: Steam reforming; Ethanol; Nickel catalyst; Calcium oxide; Stability; Coke mechanism; Surface OH groups; Water adsorption;
Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al2O3: II. Acidity/basicity, water adsorption and catalytic activity by Catherine K.S. Choong; Lin Huang; Ziyi Zhong; Jianyi Lin; Liang Hong; Luwei Chen (155-162).
Display Omitted► Ni/Ca-Al2O3 suitable for low temperature ethanol steam reforming (ESR). ► Ca diminishes the acidic OH groups on Al2O3, depressing ethylene formation. ► Ca increases water adsorption, providing abundance of adsorbed OH groups. ► The OH groups enhance ethanol adsorption, promoting conversions to H2, CH4 and CO2.The effect of Ca modification to Ni/Al2O3 catalysts in ethanol steam reforming was studied by using a 5-channel micro-reactor, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed desorption (TPD) of probe molecules H2O, NH3, CO2 and ethanol. Both Al2O3 and Ca-modified Al2O3 supports are not catalytically active for the ethanol reforming. But in the presence of the active metal Ni, the catalytic performance of Ni/Ca-Al2O3 is far more superior to Ni/Al2O3 for low temperature H2 production. The introduction of Ca greatly reduces the acidity of Al2O3, depressing ethanol dehydration and ethylene formation. It brings about positive attributes such as increasing water adsorption, providing Ni catalyst the proximity and abundance of adsorbed OH groups. The involvement of OH groups in the reactions in turn enhances the ethanol adsorption, stabilizes its adsorbate intermediates for further conversions to H2, CH4 and CO2 at relatively low temperatures. This paper therefore serves to illustrate the importance of acidity and steam adsorption capacity in the design of the catalysts for ethanol steam reforming.
Keywords: Steam reforming; Ethanol; Nickel catalyst; Calcium oxide; Acidity; Surface OH groups; Water adsorption;
Catalytic asymmetric epoxidation of unfunctionalized olefins using a series novel type of layered crystalline organic polymer–inorganic hybrid zinc phosphonate–phosphate immobilized aryldiamine modified chiral salen Mn(III) complex by Jing Huang; Xiangkai Fu; Qiang Miao (163-172).
Display Omitted► Organic polymer–inorganic hybrid material layered crystalline ZnPS–PVPA was synthesized and characterized. ► The chiral salen Mn(III) was immobilized on aryldiamine modified ZnPS–PVPA. ► The heterogeneous catalysts displayed superior activity according to the homogeneous catalysts. ► The heterogeneous catalysts could be reused at least nine times without significant loss of activity. ► The catalysts could be used in large-scale reactions with superior catalytic disposition.In this report we demonstrate the suitability of layered crystalline organic polymer–inorganic hybrid material ZnPS–PVPA with different content of the organic group and different inorganic phosphate as catalyst supports for asymmetric catalysis. A series of the chiral salen Mn(III) complex immobilized onto ZnPS–PVPA modified by aryldiamine were synthesized and characterized by FT-IR, diffusion reflection UV–vis, AAS, N2 volumetric adsorption, SEM, TEM, XRD and TG. The supported catalysts displayed superior catalytic activities in the asymmetric epoxidation of α-methylstyrene and indene with m-CPBA and NaIO4 as oxidants, compared with the corresponding homogeneous catalyst (ee, >99% vs 54% and >99% vs 65%). And the heterogeneous catalysts are relatively stable and can be recycled nine times in the asymmetric epoxidation of α-methylstyrene. These results revealed that the special structure of ZnPS–PVPA played vital impacts on the conversion and enantioselectivity. Furthermore, this novel type of catalyst can also be validly used in large-scale reactions with superior catalytic disposition being maintained at the same level, which possessed the potentiality for application in industry.
Keywords: Chiral Mn(III) salen; Zinc poly(styrene-phenylvinyl phosphonate)-phosphate; Heterogeneous catalyst; Asymmetric epoxidation;
Kinetic study of the hydrogenation of p-nitrophenol to p-aminophenol over micro-aggregates of nano-Ni2B catalyst particles by Firoozeh Taghavi; Cavus Falamaki; Alimemad Shabanov; Leila Bayrami; Amir Roumianfar (173-180).
Display Omitted► A nano-particle Ni2B catalyst has been synthesized under various conditions. ► Its performance for a direct hydrogenation reaction has been investigated. ► The reaction is the transformation of p-nitrophenol to p-aminophenol by hydrogen. ► The catalyst shows a better activity with respect to Raney nickel. ► The reaction mechanism has been determined.The present work concerns a thorough investigation of the performance of a nano-nickel boride catalyst for the direct hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) in a batch slurry reactor using ethanol as solvent. The effect of pH during the synthesis procedure on the properties of the as-synthesized catalyst has been investigated using FTIR, XRD, ICP and FESEM analysis. The synthesized catalyst shows a better activity with respect to Raney nickel. The effect of catalyst preparatory method on its activity has been investigated. The effect of reaction temperature (40–80 °C), PNP initial concentration (0.07–0.28 g mL−1) and initial pressure (25–40 bar) on the reaction kinetics has been investigated. It has been shown that the kinetic behavior throughout the whole time domain could be reasonably predicted considering a single site mechanism with atomically adsorbed hydrogen and PNP adsorption as the controlling step.
Keywords: Nickel boride; Hydrogenation; p-Aminophenol; p-Nitrophenol; Nano-catalyst;
Synthetic layered and tube-like silica nanoparticles as novel supports for metallocene catalysts in ethylene polymerization by Paula A. Zapata; Raúl Quijada; Ingo Lieberwirth; Humberto Palza (181-187).
Display Omitted► Metallocene catalyst was supported on synthetic hybrid layered and tube-like silica. ► The catalytic activities of support systems were comparable to a homogeneous system. ► The morphology of the support influences in the catalytic activity. ► The molecular weight of the polymers increase for the supported systems. ► The addition of nanoparticles improve the thermal stability of the PE.Synthetic hybrid layered (HLNP) and tube-like (SNTP) silica nanoparticles were used to support the (nBuCp)2ZrCl2 metallocene catalyst for ethylene polymerization. Different amounts of zirconium were directly supported on the nanoparticles either with or without methylaluminoxane (MAO) treatment, allowing the effect of catalyst loading and particle surface on catalytic behaviour and polymer properties to be studied. Our results show that outstanding catalytic activities, comparable to a homogeneous polymerization, can be obtained when the metallocene catalyst is directly supported on the silica nanoparticles. The catalytic activity of the metallocene catalyst supported on MAO-treated nanoparticles increases with the amount of zirconium in the support. The molecular weights of the polyethylenes synthesized using both supported systems were higher than those from homogeneous polymerization. TEM images show that both nanoparticles were well dispersed in the polymer matrix and the HLNPs were exfoliated into the polymer. The presence of these nanoparticles in the resulting polymer improves the thermal stability of the matrix.
Keywords: Supported metallocene; Nanocomposites; Ethylene polymerization; Synthetic nanolayer; Synthetic nanotubes;
Catalysis and characterization of carbon-supported ruthenium for cellulose hydrolysis by Tasuku Komanoya; Hirokazu Kobayashi; Kenji Hara; Wang-Jae Chun; Atsushi Fukuoka (188-194).
Display Omitted► Ru/CMK-3 shows high activity and durability for the hydrolysis of cellulose in water. ► Ru species hydrolyzes cellobiose to glucose without adding any mineral acids. ► Ru on CMK-3 is revealed to be hydrous Ru oxide by physicochemical measurements. ► The hydrous Ru oxide is easily prepared by a conventional impregnation method.Ru catalyst supported on mesoporous carbon CMK-3 shows high activity and durability for the hydrolysis of cellulose to glucose in hot compressed water at 503 K. The Ru/CMK-3 catalyst also hydrolyzes cellobiose to glucose in water at 393 K. Several physicochemical methods such as XRD, TEM, XPS, H2-TPR, O2-titration, and XAFS were used to characterize active Ru species on CMK-3 and to clarify the formation pathway of the active species. From these studies, we conclude that hydrous Ru oxide RuO2·2H2O is formed on CMK-3 after H2-reduction of RuCl3/CMK-3 at 673 K and subsequent passivation at room temperature, and that the Ru oxide nanoparticles with a mean diameter of 1.1 nm are highly dispersed on CMK-3.
Keywords: Biomass; Cellulose; Hydrolysis; Glucose; Supported Ru catalyst; Hydrous ruthenium oxide;
Synthesis of Pt–Co nanoparticles on multi-walled carbon nanotubes for methanol oxidation in H2SO4 solution by R.S. Amin; K.M. El-Khatib; R.M. Abdel Hameed; Eglal R. Souaya; Mohamed A. Etman (195-203).
Display Omitted► Pt Co nanodeposits with particle size of 2–5 nm are formed. ► Higher amount of Co in Pt–Co/CNTs “×40” is reduced. ► Pt–Co/CNTs “×70” electrode records the lowest potential of methanol oxidation. ► Pt–Co/CNTs “×70” electrode showed long-term cycleability and CO tolerance.Pt and Pt–Co supported on MWCNTs were synthesized by the impregnation method using NaBH4 as the reducing agent. The effect of varying NaBH4 concentration on particle size, morphology and chemical composition of Pt–Co/MWCNTs was studied. A homogeneous distribution of Pt–Co nanodeposits with particle size of 2–5 nm was attained in TEM images at Pt–Co/MWCNTs “×70” powder. EDX analysis confirmed the reduction of higher amount of Co in Pt–Co/MWCNTs “×40” electrocatalyst. The electrochemical activity of Pt/MWCNTs and Pt–Co/MWCNTs electrocatalysts was examined towards methanol oxidation reaction in 0.5 M H2SO4 solution by employing the cyclic voltammetry and the chronoamperometry techniques. The lowest onset potential and the highest oxidation current density were gained at Pt–Co/MWCNTs “×70” electrocatalyst. Its good stability over the long-term performance study elects it as a promising candidate for the DMFCs applications.
Keywords: Platinum–cobalt; Methanol oxidation; Fuel cells; MWCNTs; Electrocatalyst;
Comparative study of NiLaZr and CoLaZr catalysts for hydrogen production by ethanol steam reforming: Effect of CO2 injection to the gas reactants. Evidence of Rh role as a promoter by Nicolas Bespalko; Anne-Cécile Roger; Juan Bussi (204-210).
Display Omitted► NiLaZr and CoLaZr catalysts displayed high activity for the ethanol steam reforming. ► Trimetallic oxides show high selectivity for hydrogen production. ► Rh doped catalysts improves the activity and selectivity for hydrogen production. ► The injection of CO2 to the reactant gas decreases the hydrogen selectivity. ► Oxycarbonate species leads to a highly efficient carbon gasification.The catalytic performance of trimetallic oxides MeLaZr (Me: Ni, Co) was evaluated in the steam reforming of ethanol for hydrogen production. Rh doped and non doped catalysts were prepared by the pseudo sol–gel like method, characterized by X-ray diffraction (XRD), thermo-programmed reduction (TPR), micro-homogeneity analysis (TEM-EDXS), specific surface areas (BET). A phase-segregation process takes place during the calcination for both trimetallic systems leading to the formation of La2Zr2O7 pyrochlore-type compound in coexistence with the Me-oxide. NiLaZr and CoLaZr catalysts show high activity and high selectivity for hydrogen production. Addition of Rh promotes reducibility at lower temperatures for both trimetallic catalysts and remarkably improves the activity and selectivity for H2. The H2 selectivity is lowered by CO2 injection because of the increase of the rate of the reverse WGSR and/or methanation reaction. The CH4 selectivity is lowered by the dry reforming reaction. The key-role played by oxycarbonate species formed during the reforming tests leads to a highly efficient gasification of carbon deposits by the Boudouard reaction.
Keywords: Ethanol steam reforming; Hydrogen production; Trimetallic oxides; Pyrochlore-type compound; Oxycarbonate species;
Highly active photocatalytic ZnO nanocrystalline rods supported on polymer fiber mats: Synthesis using atomic layer deposition and hydrothermal crystal growth by Bo Gong; Qing Peng; Jeong-Seok Na; Gregory N. Parsons (211-216).
Display Omitted► Polymer fibers can support highly active nanocrystalline oxide photocatalysts. ► Atomic layer deposition forms a uniform seed layer for ZnO nanorod growth. ► Supported catalyst prevents the aggregation of active nanocrystals. ► Nanocrystals on fibers show superior photocatalytic degradation of organics.Photocatalytically active zinc oxide nanocrystalline rods are grown on high surface area polybutylene terephthalate (PBT) polymer fiber mats using low temperature solution based methods, where the oxide crystal nucleation is facilitated using conformal thin films formed by low temperature vapor phase atomic layer deposition (ALD). Scanning electron microscopy (SEM) confirms that highly oriented single crystal ZnO nanorod crystals are directed normal to the starting fiber substrate surface, and the extent of nanocrystal growth within the fiber mat bulk is affected by the overall thickness of the ZnO nucleation layer. The high surface area of the nanocrystal-coated fibers is confirmed by nitrogen adsorption/desorption analysis. An organic dye in aqueous solution in contact with the coated fiber degraded rapidly upon ultraviolet light exposure, allowing quantitative analysis of the photocatalytic properties of fibers with and without nanorod crystals present. The dye degrades nearly twice as fast in contact with the ZnO nanorod crystals compared with samples with only an ALD ZnO layer. Additionally, the catalyst on the polymer fiber mat could be reused without need for a particle recovery step. This combination of ALD and hydrothermal processes could produce high surface area finishes on complex polymer substrates for reusable photocatalytic and other surface-reaction applications.
Keywords: Atomic layer deposition; Nonwoven fiber; Diethyl zinc; Zinc oxide; Nanocrystals; Nanorods; Hydrothermal; Photocatalytic;
Enhancement of visible-light photocatalytic efficiency of BiOCl/Bi2O3 by surface modification with WO3 by Ashok Kumar Chakraborty; Sher Bahadur Rawal; Song Yi Han; Seung Yong Chai; Wan In Lee (217-223).
Display Omitted► Visible-light photocatalytic activity of BiOCl/Bi2O3 was enhanced by WO3 coverage. ► In evolution of CO2 from 2-propanol, its activity was enhanced by 2.7 times. ► Photocatalytic activity of WO3/BiOCl/Bi2O3 was 1.7 times that of N-doped TiO2. ► Surface coverage of WO3 improved the chemical stability of BiOCl/Bi2O3.The visible-light photocatalytic efficiency of BiOCl/Bi2O3 composites was notably enhanced by covering their surfaces with monolayer of WO3. The photocatalytic activity of WO3/BiOCl/Bi2O3 in decomposing gaseous 2-propanol (IP) and aqueous 1,4-terephthalic acid (TPA) under visible-light irradiation (λ ≥ 420 nm) was maximized by introducing a 0.6 mol% of WO3 to BiOCl/Bi2O3, whereas further increases of WO3 sharply decreased its activity. This suggests that monolayer coverage of BiOCl/Bi2O3 with molecular WO3 optimizes photocatalytic activity, and therefore, that the role of WO3 is to improve the adsorption affinity of BiOCl/Bi2O3 toward OH−, H2O, and organic species. In the evolution of CO2 from IP, 0.6%WO3/BiOCl/Bi2O3 exhibited 2.7 times the photocatalytic efficiency of bare BiOCl/Bi2O3. Remarkably, its efficiency was estimated to be 1.7 times that of typical N-doped TiO2. Moreover, it was found that the surface coverage of WO3 greatly extended the chemical stability of BiOCl/Bi2O3 during photocatalytic reaction.
Keywords: Photocatalyst; Visible-light; Heterojunction; WO3; BiOCl/Bi2O3; 2-propanol; CO2 evolution; Terephthalic acid;
Toluene decomposition using silver vanadate/SBA-15 photocatalysts: DRIFTS study of surface chemistry and recyclability by Wen-Sheng Chang; Yu-Chu M. Li; Tsair-Wang Chung; Yung-Sen Lin; Chao-Ming Huang (224-230).
Display Omitted► SVO/SBA-15 composite was synthesized using a wetness impregnation procedure. ► SVO/SBA-15 has a much higher photodegradation ability than those of P25 and SVO. ► The mass spectra prove the main oxidation intermediate of toluene is benzaldehyde. ► A favorable crystalline phase, Brønsted, and Lewis acids are responsible for photoactivity.Silver vanadate (SVO) containing SBA-15 visible-light-driven photocatalyst was synthesized using the incipient wetness impregnation procedure. X-ray diffraction (XRD) results reveal that the SVO/SBA-15 powders consisted of three kinds of phase: pure Ag4V2O7 or pure α-Ag3VO4 or mixed phases of Ag4V2O7 and α-Ag3VO4. The mass spectra indicate that the main oxidation intermediate of toluene is benzaldehyde. The sample loaded with 51 wt% SVO (51SVO/SBA-15) exhibited the best photocatalytic activity. The results of two consecutive cyclic runs and regeneration indicate that the accumulation of benzaldehyde causes an irreversible deactivation of P25, but no deactivation of 51SVO/SBA-15. The enhanced photocatalytic activity of 51SVO/SBA-15 is attributed to mixed crystalline phases of Ag4V2O7 and α-Ag3VO4, where α-Ag3VO4 is the major component. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms the presence of Brønsted and Lewis acids on the SVO/SBA-15 composites. A favorable crystalline phase combined with high intensities of Brønsted and Lewis acids is considered the main cause of the enhanced adsorption capacity, outstanding photoactivity, and long term stability of the SVO/SBA-15 composites.
Keywords: SBA-15; Visible-light-driven photocatalyst; Toluene photo-oxidation; Brønsted and Lewis acids;
Promotion effect of support calcination on ethanol production from CO hydrogenation over Rh/Fe/Al2O3 catalysts by Weimiao Chen; Yunjie Ding; Xiangeng Song; Tao Wang; Hongyuan Luo (231-237).
.Display Omitted► Effect of Al2O3 calcination on ethanol production from syngas over Rh/Fe/Al2O3. ► CO conversion value was first delved into four pathways. ► CO desorption behaviors of Rh-based catalysts during CO-TPSR experiment.A series of Rh/Fe/Al2O3 catalysts, in which the Al2O3 supports were calcined at different temperatures, were prepared by a sequential impregnation method. The catalysts were tested by CO hydrogenation and characterized by N2 adsorption–desorption, X-ray diffraction (XRD), CO pulse chemisorption, temperature programmed surface reaction (TPSR) and temperature programmed reduction (TPR) techniques. The activity of ethanol formation was the highest when the catalyst support was calcined at 800 °C, while that of methanol formation increased continuously with the calcination temperature of the support. According to the commonly accepted mechanism of C2-oxygenates formation, CO conversion followed three separate pathways after CO dissociation, and our results suggested that the activity towards CO insertion and dissociation increased gradually with the calcination temperature, but began to decrease at 900 °C. On the other hand, direct hydrogenation of CO to methanol was still increasing at 900 °C. These observations were in agreement with TPSR results. Dispersion of the Rh or Fe species was not impaired, and even improved, with the declining of the surface area of the support due to high temperature calcination. TPR results revealed that Rh–Fe interaction was strengthened after calcination, due to a lowering in surface hydroxyl reactivity of the support and an increase of the Rh–Fe interface area. As a result, the amount of Rh–Fe–O sites for CO dissociation and insertion increased with the calcination temperature, giving rise to the increase in ethanol formation activity. However, an over-strong Rh–Fe interaction would be resulted when the catalyst support was calcined at 900 °C, and this would cause more Fe species to be reduced, which would then cover the Rh sites. Consequently, CO uptake as well as dissociation and insertion of CO would decrease, leading to more CO molecules being hydrogenated directly to methanol, thus causing a decrease in the selectivity of ethanol formation.
Keywords: Rhodium; Alumina; Iron; Carbon monoxide hydrogenation; Calcination temperature; Ethanol;