Applied Catalysis A, General (v.479, #C)

Contents (iii-vi).

Multifunctional cyclodextrin-based N,N-bidentate ligands for aqueous Heck arylation by Jonathan Potier; Stéphane Menuel; Jolanta Rousseau; Sigitas Tumkevicius; Frédéric Hapiot; Eric Monflier (1-8).
Novel Pd(II) complexes coordinated by N,N-bidentate ligands derived from cyclodextrins have been synthesized by copper-catalyzed azide alkyne 1,3-cycloaddition (CuAAC). Depending on the nature of the N,N-bidentate ligand, fast or slow equilibriums between the free N,N-bidentate ligand and the Pd-species were detected by NMR measurements. The new Pd(II) complexes acted as efficient water soluble catalysts for the Heck reaction of aryl iodides in aqueous medium. The reaction could tolerate aerobic conditions and affords the coupling products in good yields. Once the reaction was complete, the product and the catalyst could be recovered separately by simple decantation.
Keywords: Cyclodextrins; Palladium; Aqueous catalysis; Heck reaction;

Porous γ-Al2O3 support with improved mechanical strength was synthesized via sol gel method in granular form having different mesh sizes i.e., 0.60–1.0 mm and 2.0–2.8 mm, followed by rehydration at room temperature and calcination at 1023 K, and was employed for the preparation of Ir and Ru catalysts by impregnation method. The structural features of supports, Ir/γ-Al2O3 and Ru/γ-Al2O3 catalysts were characterized by N2 physiosorption, H2 chemisorption, crushing strength measurements, XRD, SEM, and TEM. The catalytic activity was evaluated for hydrazine decomposition in a 1 N microthruster at ambient temperature.
Keywords: γ-Al2O3 supported catalysts; Iridium; Ruthenium; Hydrazine decomposition;

Modifications in the HZSM-5 zeolite for the selective transformation of ethylene into propylene by Eva Epelde; Andrés T. Aguayo; Martin Olazar; Javier Bilbao; Ana G. Gayubo (17-25).
Propylene production in the transformation of ethylene has been studied on HZSM-5 zeolite catalysts of different SiO2/Al2O3 ratio (30, 80 and 280), doped (1 wt.%) with K or P or treated by mild in situ steaming, in order to attenuate their acidity. The experiments have been carried out in a fixed bed reactor at 500 °C, space time of 3.2 ( g catalyst h ) ( mol CH 2 ) − 1 and time on stream up to 15 h. The results highlight the effect catalyst acidity has on ethylene conversion, catalyst stability (deactivation by coke deposition) and propylene yield. The balance between these indices entails the use of a zeolite of moderate acidity subjected to a mild treatment in order to maintain a suitable activity for propylene formation by oligomerization-cracking reactions, and thus minimizing secondary reactions of hydrogen transfer and aromatization. A propylene yield of 37% is obtained for a time on stream of 11.3 h with the HZSM-5 zeolite catalyst of SiO2/Al2O3  = 80 modified by mild in situ steaming treatment.
Keywords: HZSM-5 zeolite; Propylene; Ethylene; Deactivation; Acidity;

Highly selective Pd–Cu/ZnAl2O4 catalyst for hydrogen production by Pawel Mierczynski; Krasimir Vasilev; Agnieszka Mierczynska; Waldemar Maniukiewicz; Tomasz P. Maniecki (26-34).
This paper deals with the study of the bimetallic Pd–Cu and monometallic Cu catalyst in steam reforming of methanol. FTIR spectroscopy, X-ray diffraction (XRD) and XPS techniques were used to characterize both mono and bimetallic catalysts. This study presents evidence of Pd–Cu formation in copper catalysts supported on spinel structure ZnAl2O4 during reduction in 5%H2–95%Ar mixture at 300 °C in the presence of palladium. The intermetallic compound is formed by a spillover effect between Pd and Cu.
Keywords: Pd–Cu/ZnAl2O4; Pd–Cu; Alloy; Monometallic catalyst; Bimetallic catalyst;

Experimental evidences of the relationship between reducibility and micro- and nanostructure in commercial high surface area ceria by José M. Gatica; Diana M. Gómez; Juan C. Hernández-Garrido; José J. Calvino; Gustavo A. Cifredo; Hilario Vidal (35-44).
Two commercial high BET surface areas CeO2 are characterized, as received and after calcination at different temperatures, to better understand the relationship between reducibility and micro- and nanostructure. Combination of TPR data, Rietveld analysis of XRD diagrams and HREM/HAADF-STEM suggest that the nano-particles are responsible for Ce4+ reduction in the moderate temperature range. Results obtained in this work show that previous models based on kinetic and theoretical analysis can be fully supported by morphological characterization. This study unveils the key parameters that must be known in order to select appropriate commercial ceria samples.
Keywords: CeO2; Reduction behaviour; Nanostructure; Rietveld analysis; HAADF-STEM.;

Aqueous transfer hydrogenation using Noyori's catalyst (η 6-arene)Ru(H)TsDPEN (TsDPEN =  N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine) was found to be dependent on the substrate/catalyst ratio. The reaction was suppressed when a large amount of substrate (acetophenone) was used. To relieve this substrate inhibition problem, common phase transfer catalysts were applied to transfer the formate anion from aqueous layer to organic substrate layer. Quaternary ammonium salts with long alkyl chains were shown to enhance the hydrogenation reactivities up to 5 times. The reaction conditions, including formate loading, phase transfer catalyst loading, amount of water, temperature, stirring speed and counterions, were optimized to afford the best catalytic activities.
Keywords: Phase transfer catalysis; Transfer hydrogenation; Metal–ligand bifunctional catalyst;

In this article, a successful design on translating a heterogeneous catalysis of chiral zirconium phosphonate-supported ruthenium catalyst into a homogeneous system was developed by the covalent attachment of chiral (R,R)-1,2-diphenyl-ethylenediamine [(R,R)-DPEN] into the backbone of zirconium phosphonate with the different arm lengths (n = 2, 4, 6) and immobilization of [RuCl2(p-cymene)]2. Their catalytic performances in the homogeneous asymmetric transfer hydrogenation of unsymmetrical benzils with m- and p-substituents were enhanced, and the excellent activities (>97.1% conv.), diastereomeric and enantiomeric purities (syn/anti  = 11.0–29.4, 91.8–99.2%ee syn) were achieved. These homogeneous supported Ru catalysts could be quantitatively and readily recovered by addition of ethyl acetate and centrifugation by solid/liquid separation, and be reused for five times without significant loss of their catalytic performances with 97.0% conv., 95.6% syn and syn/anti  = 20.7.
Keywords: Zirconium phosphonate; Homogeneous catalysis; Asymmetric hydrogenation; Unsymmetrical benzil; Ruthenium;

X-ray absorption, X-ray diffraction and electron microscopy study of spent cobalt based catalyst in semi-commercial scale Fischer–Tropsch synthesis by Nikolaos E. Tsakoumis; Roya Dehghan-Niri; Magnus Rønning; John C. Walmsley; Øyvind Borg; Erling Rytter; Anders Holmen (59-69).
Calcined, reduced and spent Co-Re/γ-Al2O3 catalysts for Fischer–Tropsch synthesis (FTS) were characterized and compared. Co-K-edge and Re-LIII-edge X-ray absorption near edge structure (XANES), X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and H2 chemisorption were used to provide insight into structural transformations that the catalyst experiences during a month of operation in a semi-commercial FTS plant. Results from the core techniques for nanoparticle size determination suggest that sintering of the cobalt crystallites is an important deactivation mechanism in FTS performed in slurry reactors. In addition, a higher degree of reduction is observed for the spent catalytic material, while Re appears in a partially reduced state before and after reaction. The particle size distribution together with the spread of Co nanoparticles on the γ-Al2O3 surface indicates crystallite migration as the prevailing mechanism.
Keywords: Fischer–Tropsch; Cobalt; Deactivation; Sintering; Gas-to-liquid;

The possible reaction mechanism over the V-MCM-41 catalyst for the selective oxidation of cyclohexane.V-MCM-41 with high content of vanadium in the framework was synthesized by using direct hydrothermal method under alkaline condition. Tartaric acid is the complexing reagent and cetyltrimethylammonium bromide is the structure-directing agent. The samples were characterized by X-ray fluorescence, X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption–desorption, Fourier-transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy techniques. The catalytic performance for the selective oxidation of cyclohexane was also examined. The results showed that the vanadium atoms were successfully introduced into the MCM-41 framework and the vanadium content reached up to 8.1 wt.%. Moreover, the V-MCM-41 samples possessed regular and stable structure with high specific surface area (692–939 m2  g−1), large pore diameter (3.6–4.6 nm) and large pore volume (0.86–0.95 cm3  g−1). The samples exhibited excellent catalytic performance of up to 22.57% cyclohexane conversion and 99.53% selectivity for cyclohexanone and cyclohexanol in the cyclohexane oxidation.
Keywords: Heteroatom molecular sieve; Framework vanadium atoms; Cyclohexane selective oxidation; Cyclohexanol; Cyclohexanone;

The catalytic etherification of glycerol using calcium–lanthanum oxide supported on MCM-41 as a stable heterogeneous basic catalyst was investigated. Stable heterogeneous mesoporous basic catalysts were synthesized by wet impregnation of MCM-41 with calcium nitrate and lanthanum nitrate. The surface and structural properties of the prepared catalysts were when characterized using different techniques. MCM-41 and modified MCM-41 were used in the solventless etherification of glycerol to produce diglycerol as the desired product. The reaction was performed at 250 °C for 8 h, and catalyst activity was evaluated. Catalytic etherification over the 20%Ca1.6La0.6/MCM-41 catalyst resulted in the highest glycerol conversion of 91% at the diglycerol yield of 43%. The distribution of diglycerol isomer in the etherification of glycerol was studied, and the value of the sum of two dimers (ββ′ + αβ = 67%) was found to be higher than that of αα′ dimer (33%) after 8 h of reaction. Thus, the major reaction occurred inside the porous area instead of the external surface area.
Keywords: Glycerol; Catalytic etherification; Supported MCM-41; Diglycerol isomer;

Catalyst design for methane steam reforming by Viswanathan Arcotumapathy; Dai-Viet N. Vo; Dean Chesterfield; Cao T. Tin; Arman Siahvashi; Frank P. Lucien; Adesoji A. Adesina (87-102).
Commercial syngas production via methane steam reforming is conventionally carried out over Ni catalyst supported on semiconductor oxides such as Al2O3 and SiO2. The present work reports empirical verification of catalyst design for methane steam reforming carried out at relatively low steam-to-carbon feed ratio (2:1–2:1) and compares the behavior among SiO2, SBA-15 (mesoporous silica), γ-Al2O3 and α-Al2O3 supported Ni catalyst. In addition promoters such as B, Ce, Mo and Zr were assessed. SBA-15 and Ce emerged to be significant support and promoter respectively. However there seems to be an optimum Ni wt% loading for a given support which was found to be 10 wt% for SBA-15. The investigations revealed that MSR over 1 wt% Ce/10 wt% Ni/SBA-15 at S:C = 1–2 at atmospheric pressure and 1073 K resulted in 92–99% methane conversion with higher H2 to CO ratio and highly resistant to carbon deposition.
Keywords: Methane steam reforming; Supports; Promoters; Low steam-to-carbon; Catalyst design;

Bimetallic Ag–Au/SiO2 catalysts: Formation, structure and synergistic activity in glucose oxidation by Tímea Benkó; Andrea Beck; Krisztina Frey; Dávid Ferenc Srankó; Olga Geszti; György Sáfrán; Boglárka Maróti; Zoltán Schay (103-111).
SiO2 supported Ag–Au bimetallic catalysts were prepared by sol adsorption method with 10/90, 20/80, 33/67, and 50/50 Ag/Au molar ratios. Reduction of HAuCl4 in Ag sol resulted in alloyed Ag–Au colloid particles and that structure remained after calcination and reduction treatment. The alloy structure of the catalysts was confirmed by UV–visible spectroscopy and high resolution transmission electron microscopy. The Au–Ag bimetallic effect and its dependence on the Ag/Au molar ratio was studied in glucose oxidation where synergistic activity increase was observed compared to the Au/SiO2 reference sample in the case of the bimetallic samples with less than Ag/Au = 50/50 molar ratio. The Ag/SiO2 was inactive at the same conditions. The Ag/Au surface atomic ratios – calculated by X-ray photoelectron spectroscopy (XPS) – were slightly higher than in the bulk—determined by prompt gamma activation analysis (PGAA). The higher activity of the bimetallic samples is suggested to be caused by the improved O2 activating ability provided by Ag sites. The further increase of Ag loading above the optimal concentration may dilute or cover the Au to such an extent that the number of gold ensembles necessary for glucose activation decreases deteriorating the activity.
Keywords: Ag–Au nanoparticle; Glucose oxidation; Synergistic effect; Bimetallic catalyst; Gold catalysis;

In this paper, palladium-DABCO complex supported on γ-Fe2O3 magnetic nanoparticles (Pd-DABCO-γ-Fe2O3) was synthesized and characterized by HRTEM, SEM, XRD, XPS, ICP, FT-IR, TGA, VSM and elemental analysis. The synthesized catalyst was successfully applied as a new magnetically recyclable heterogeneous catalyst in Mizoroki⬜Heck cross-coupling reaction of aryl halides with alkyl acrylates and styrene under solvent-free conditions.
Keywords: Palladium; Magnetic nanoparticle; Heterogeneous catalyst; Mizoroki⬜Heck; DABCO;

Since triolein is the main constituent of most oils such as olive and high oleic sunflower oils, self-metathesis of this triacylglycerol at mild reaction conditions was investigated via a heterogeneous approach, in the presence of ZnCl2-modified mesoporous alumina supported methyltrioxorhenium (MTO) as a catalyst. Both intra and intermolecular metathesis reactions were observed. While, 9-octadecene, dimers and trimers of the triacylglycerol were isolated, intermolecular cyclization metathesis products were also obtained. The MTO-based catalyst was found to be highly chemoselective affording only desired metathesis product formation. In contrast, more than 50% of triolein was converted to undesired solid product in the presence of the homogeneous Grubbs 2nd generation catalyst. Triolein metathesis products were effectively separated by chromatographic techniques and identified using mass spectrometric and NMR analyses. The reported results show that 3%MTO/ZnCl2–Al2O3-meso is an efficient and selective heterogeneous catalyst for bulky functionalized olefins metathesis such as triacylglycerols and edible oils, avoiding the use of costly homogeneous catalysts, or the use other rhenium-based catalysts with toxic promoters such as R4Sn.
Keywords: Self-metathesis; Triolein; Methyltrioxorhenium (MTO); ZnCl2-promoted mesoporous alumina; Metathesis polymerization;