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Applied Catalysis A, General (v.375, #2)

Editorial Board (pp. co2).

Contents (pp. iii-vii).

Surface properties of copper in different solvent mother solutions: A density functional theory study by Zhijun Zuo; LuLu Sun; Wei Huang; Peide Han; Zhihong Li (pp. 181-187).

The results show that the surface energies of Cu( h k l) surface are very sensitive to the COSMO solvent model. When CO molecules adsorb on the Cu( h k l) surface in chloroform, liquid paraffin and vacuum, the solvent effects can improve the stability of CO adsorption on Cu( h k l) surface and the ability of CO activation.We use density functional theory (DFT) combined with conductor-like solvent model (COSMO) to study different solvent mother solution–copper interfacial properties, which are believed to play a key role in the “one-pot” synthesis of dimethyl ether (DME) from syngas in a slurry reactor. For three relevant crystallographic planes – (111), (110), and (100) – we develop a theoretical approach for calculating surface energies which cannot be determined experimentally. The surface energies show that the solvent not only has a strong effect on copper morphology, but also affects the Mulliken charges of Cu( h k l) surfaces. We also study CO molecules adsorbing on Cu( h k l) surfaces. It is found that both the structural parameters and the relative energies of CO are very sensitive to the COSMO solvent model. Thus the solvent effects can improve the stability of CO adsorption on Cu( h k l) surface and the ability of CO activation. This analysis gives us some new insights into the understanding of solvent effects.

Keywords: DFT; CO; Cu; Solvent effects; Adsorption

Catalytic characterization of pure SnO₂ and GeO₂ in methanol steam reforming by Qian Zhao; Harald Lorenz; Stuart Turner; Oleg I. Lebedev; Gustaaf Van Tendeloo; Christoph Rameshan; Bernhard Klötzer; Jürgen Konzett; Simon Penner (pp. 188-195).

We demonstrated the catalytic activity and selectivity of SnO/SnO₂ and GeO₂ in methanol steam reforming, in close correlation to oxides in the 3rd main group of the periodic system, namely Ga₂O₃ and In₂O₃. It was shown that the catalytic selectivity of In₂O₃ and SnO₂ towards CO₂ is very pronounced. In contrast, Ga₂O₃ and GeO₂ are less CO₂ selective but exhibit very similar reaction profiles.Structural changes of a variety of different SnO, SnO₂ and GeO₂ catalysts upon reduction in hydrogen were correlated with associated catalytic changes in methanol steam reforming. Studied systems include SnO, SnO₂ and GeO₂ thin film model catalysts prepared by vapour phase deposition and growth on polycrystalline NaCl surfaces and, for comparison, the corresponding pure oxide powder catalysts.Reduction of both the SnO₂ thin film and powder at around 673K in 1bar hydrogen leads to a substantial reduction of the bulk structure and yields a mixture of SnO₂ and metallic β-Sn. On the powder catalyst this transformation is fully reversible upon oxidation in 1bar O₂ at 673K. Strongly reduced thin films, however, can only be re-transformed to SnO₂ if the reduction temperature did not exceed 573K. For GeO₂, the situation is more complex due to its polymorphism. Whereas the tetragonal phase is structurally stable during reduction, oxidation or catalytic reaction, a small part of the hexagonal phase is always transformed into the tetragonal at 673K independent of the gas phase used.SnO₂ is highly active and CO₂ selective in methanol steam reforming, but the initial high activity drops considerably upon reduction between 373 and 573K and almost complete catalyst deactivation is observed after reduction at 673K, which is associated with the parallel formation of β-Sn. In close correlation to the structural results, the catalytic activity and selectivity can be restored upon an oxidative catalyst regeneration at 673K. Tetragonal GeO₂ exhibits only a small activity and no pronounced selectivity to either CO or CO₂, at least after reduction. In its fully oxidized state release of surface/lattice oxygen results in a non-catalytic formation of CO₂ by oxidation of CO originating from catalytic dehydrogenation.

Keywords: Electron microscopy; EELS; SnO; ₂; SnO; GeO; ₂; Methanol steam reforming; CO; ₂; selectivity

Synthesis and characterization of copper and aluminum salts of H₃PMo₁₂O₄₀ for their use as catalysts in the eco-friendly synthesis of chromanes by Daniela S. Mansilla; M. Rosario Torviso; Elba N. Alesso; Patricia G. Vázquez; Carmen V. Cáceres (pp. 196-204).

Acid catalysts based on aluminum (or copper) salts of molybdophosphoric acid were synthesized from a heteropolyacid solution to which Al₂(SO₄)₃, Al₂O(CH3COO)₄ or CuSO₄ was added. The salts were characterized by different physicochemical techniques. The catalyst acidity was measured by potentiometric titration and by temperature-programmed desorption of pyridine. The catalysts were used in the reaction between m-cresol and geraniol for the synthesis of chromanes.Acid catalysts based on aluminum (or copper) salts of molybdophosphoric acid (H₃PMo₁₂O₄₀) were prepared. They were synthesized from a heteropolyacid solution to which Al₂(SO₄)₃, Al₂O(CH3COO)₄ or CuSO₄ was added. The obtained salts were texturally characterized and a low specific surface area, between 1 and 9m²/g, was observed. The analysis of the prepared salts by ICP-AES spectrometry indicated that the molar content of Mo and P was that corresponding to the anion [PMo₁₂O₄₀]³⁻. The presence of undegraded Keggin structure was confirmed by XRD, FT-IR, DRS and³¹P MAS-NMR. The catalyst acidity was measured by means of potentiometric titration with a solution of n-butylamine in acetonitrile and by temperature-programmed desorption of pyridine. The AlPMo₁₂O₄₀ salt (from sulfate), which at 5h of reaction showed the highest conversion of m-cresol (98%) and 75% and 25% selectivity to chromane4 and3, respectively, presented the highest total acidity and, simultaneously, acid sites with maximum acid strength very high. On the other hand, Cu_0.5H₂PMo₁₂O₄₀ catalysts at 5h of reaction showed lower conversion of m-cresol than the former salt (90%) and also lower selectivity to chromane4 and3 (37% and 10%, respectively). In the latter case also 43% of open-chain compounds were observed. With the other salts, Al_0.5H_1.5PMo₁₂O₄₀, Cu₃(PMo₁₂O₄₀)₂ and AlPMo₁₂O₄₀ (from Al₂O(CH₃COO)₄), only the reaction intermediaries, open-chain compounds, were obtained because these salts presented low total acidity and acid sites with maximum acid strength very low.

Keywords: Copper and aluminum salts; H3PMo12O40; Catalysts; Eco-friendly synthesis; Chromanes

Hydrogen and ethylene production from partial oxidation of methane on CuCe, CuZr mixed oxides and ZrO₂ catalysts by Martin Schmal; Carlos A. Perez; Victor Teixeira da Silva; Liana F. Padilha (pp. 205-212).

We prepared non-stoichiometric oxides based on CuO, CeO₂ and ZrO₂ and determined main structural properties that were tested in the partial oxidation of methane (POM). XRD results indicate that Cu is finely dispersed. It indicates the presence of a Cu_xCe_yO_z phase or a solid solution. In situ XRD of the CuCe sample at different temperatures and reduction conditions was obtained to verify the influence of pretreatment. For the CuCe and ZrO₂ samples the conversion of methane increases with temperature, reaching maximum conversion at 850°C, which are close to the equilibrium values, On the other hand, the conversion for the CuZr is much lower. The ethylene selectivity increases above 700°C for CuCe and ZrO₂ and reached 92% at 850°C on the CuCe and 83% at 800°C on the ZrO₂ and on opposite, low ethylene selectivity for the CuZr catalyst. Both CuCe and ZrO₂ are excellent catalysts for ethylene production but less important for H₂ production in the partial oxidation of methane. Redox properties of CeO₂ and the presence of Cu in the CuCe catalyst favor the formation of Ce ions that may be responsible for the oxygen migration to the molecular methane and formation of CH⁻ radicals.The H₂ selectivity is approximately close to the equilibrium value between 500 and 700°C for CuCe and CuZr catalysts. No hydrogen was formed over ZrO₂. Ethylene is formed above 700°C for CuCe and ZrO₂ attaining 92% at 850°C on the CuCe and 83% at 800°C on the ZrO₂ and in opposite to H₂, low ethylene formation on the CuZr catalyst.A non-stoichiometric oxides based on CuO, CeO₂ and ZrO₂ were prepared and tested in the partial oxidation of methane (POM). XRD results indicate that Cu is finely dispersed. It indicates a Cu_xCe_yO_z phase. The H₂ selectivity is close to the equilibrium between 500 and 700°C. Ethylene is formed on CuCe and ZrO₂ attaining 92% on CuCe and 83% on the ZrO₂.

Keywords: Hydrogen; Ethylene; Mixed oxides; POM

Cracking of cyclohexane by high Si HZSM-5 by Åse Slagtern; Ivar M. Dahl; Klaus J. Jens; Trond Myrstad (pp. 213-221).

Cracking of cyclohexane has been performed over a HZSM-5 catalyst with Si/Al ratios 28, 85 and 200, in the temperature region 400–650°C and with partial pressures of cyclohexane up to 2bar. The cracking kinetics for Si/Al=200 can be adequately modelled by simple first order kinetics. Olefins and benzene appear to be the primary products from the cracking reaction, while alkanes and higher aromatics behave as secondary products. Combined selectivities of ethene+propene increase with increasing temperature, and more than 60% selectivity can be reached. Under the reaction conditions very rapid equilibration of olefins heavier than ethene is obtained.The addition of hydrogen to the cracking feed has only a small influence on the rate of formation of saturated compounds.Cracking of cyclohexane at a partial pressure of up to 2bar over HZSM-5 catalysts with Si/Al ratios 28, 85 and 200 in the temperature region 400–650°C can, at selected conditions, give more than 60% combined ethene/propene selectivity. The cracking kinetics of the Si/Al=200 catalyst can be adequately modelled by simple first order kinetics. Olefins and benzene appear to be the primary products of the cracking reaction, while alkanes and higher aromatics behave as secondary products. Under the reaction conditions very rapid equilibration of C₂₊ olefins is obtained. The addition of hydrogen to the cracking feed has only a small influence on the rate of formation of saturated compounds.

Keywords: Cyclohexane; Cracking; Zeolites; Olefins

Interaction of titanium and iron oxide with ZSM-5 to tune the catalytic cracking of hydrocarbons by Xianfeng Li; Baojian Shen; Chunming Xu (pp. 222-229).

After modification by Fe₂O₃ and TiO₂, the acidity and reduction properties of Fe–Ti/ZSM-5 improved. As a result, catalyst Fe–Ti/ZSM-5 showed a better catalytic cracking performance of n-decane and isopropyl benzene than catalysts Ti/ZSM-5, Fe/ZSM-5 or ZSM-5, such superiority indicates that Fe–Ti/ZSM-5 has potential application in the catalytic pyrolysis of heavy oil to light olefins (ethylene and propylene).In order to increase the yield of ethylene and propylene in the catalytic pyrolysis of heavy oil, ZSM-5 zeolite was modified by Fe₂O₃ and TiO₂ via pore volume impregnation. XRD, SEM, and TEM analysis indicated that the structure of the ZSM-5 remained intact after modification, and that the Ti and Fe partially entered the channels of the ZSM-5. Measurement of the number of Brønsted acid sites by n-propylamine temperature-programmed reaction and FTIR measurements showed that the Brønsted acid sites of Ti/ZSM-5 (TiO₂ loaded ZSM-5) and Fe–Ti/ZSM-5 (Fe₂O₃ and TiO₂ loaded ZSM-5) catalysts increased through the polarization function of Ti⁴⁺. DRS, XPS, and TPR results showed that the presence of Ti species improved the dispersion of Fe species on the surface of ZSM-5, whereas Fe₂O₃ promoted the reduction of TiO₂. After modification by Fe₂O₃ and TiO₂, the acidity and reduction properties of Fe–Ti/ZSM-5 improved; such improvement led to a decrease of the apparent activation energy of isopropyl benzene cracking over Fe–Ti/ZSM-5 by about 21kJ/mol compared with that over ZSM-5. As a result, catalyst Fe–Ti/ZSM-5 showed a better catalytic cracking performance of n-decane and isopropyl benzene than catalysts Ti/ZSM-5, Fe/ZSM-5 (Fe₂O₃ loaded ZSM-5) or ZSM-5.

Keywords: ZSM-5; Light olefins; Fe; ₂; O; ₃; TiO; ₂; Catalytic pyrolysis catalyst

Shape-selective dissociative adsorption of alcohols on 1-butyl-3-methylimidazolium-exchanged mordenite zeolite by Eisuke Yoda (pp. 230-235).

Dissociative alcohol adsorption was investigated on 1-butyl-3-methylimidazolium ([bmim]) exchanged mordenite (HM20) by FT-IR. Results indicated that the generation of acidic OH groups is attributable to the dissociative adsorption of alcohols on [bmim]M20 and alcohol adsorption onto the acidic OH groups. Shape-selective adsorption into the [bmim]M20 micropores was revealed for the alcohols examined.Dissociative alcohol adsorption was investigated on 1-butyl-3-methylimidazolium ([bmim]) exchanged mordenite ([bmim]M20) by Fourier transform infrared spectroscopy (FT-IR). Methanol, ethanol, 1-propanol and 2-propanol were adsorbed onto [bmim]M20. Although acidic OH groups were almost completely absent on [bmim]M20, bands attributed to hydrogen-bonded νOH of acidic OH groups (the so-called ABC triplet) were apparent for alcohol adsorption on [bmim]M20. This indicates the generation of acidic OH groups on [bmim]M20 by the dissociative adsorption of alcohols. Methanol and ethanol could diffuse into the [bmim]M20 micropores in the absence of observable energy barriers at room temperature, while energy barriers for diffusion into the micropores were observed for 1-propanol and 2-propanol at room temperature. The activation energy for diffusion of 2-propanol into the [bmim]M20 micropores was estimated as 25kJmol⁻¹. Shape-selective adsorption into the [bmim]M20 micropores was revealed for the alcohols examined.

Keywords: Mordenite; Organic cation; FT-IR

Methane dry reforming with CO₂: A study on surface carbon species by L. Guczi; G. Stefler; O. Geszti; I. Sajó; Z. Pászti; A. Tompos; Z. Schay (pp. 236-246).

Methane dry reforming with a mixture of 29% CO₂ and 71% CH₄ over 8wt% NiMgAl₂O₄ in a plug flow reactor with temperature programmed mode has been investigated. It was established that in sequential reactions the catalyst was deactivated due to graphite like carbon deposit measured by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) while by X-ray photoelectron spectroscopy (XPS) only Ni–carbide was observed. The discrepancy found by XPS and TEM can be explained by the different types of carbon species, i.e. it is assumed that after the first reaction mostly carbide is deposited, whereas after several subsequent reactions the carbon on the surface is graphitized forming carbon nanotubes (TEM). Addition of 0.5wt% gold to NiMgAl₂O₄ improves the catalytic activity and on gold containing bimetallic catalyst the formation of nanotubes is vanished. The results are interpreted by the formation of non-crystalline NiC_x which – depending on the conditions – is transferred to graphitic carbon species.In methane dry reforming on Ni/MgAl₂O₄ and Au-Ni/MgAl₂O₄ catalyst after the first reaction most of the carbon deposited is carbide (XPS), whereas after several subsequent reactions the carbon on the surface is graphitized forming carbon nanotubes (TEM). Addition of gold drastically reduces the formation of graphite and CMWNT and affect the activity of Ni.

Keywords: Methane dry reforming; Structure of coke; XRD; TEM; XPS studies

Enantioselective addition of diethylzinc to aldehydes catalyzed byd-glucosamine derivatives: Highly pronounced effect of trifluoromethylsulfonamide by Tomasz Bauer; Sławomir Smoliński (pp. 247-251).

We present the synthesis of β-hydroxy sulfonamides derived fromd-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of diethylzinc to benzaldehyde and selected aromatic and aliphatic aldehydes. The reaction is highly enantioselective for some aromatic aldehydes and enantiomeric excess up to 99% was obtained.We present the synthesis of β-hydroxy sulfonamides derived fromd-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of diethylzinc to benzaldehyde and selected aromatic and aliphatic aldehydes. The N-trifluoromethylosulfonamido-d-glucosamine derivative is one of the most active ligands known and only 1mol% of the ligand is sufficient for efficient catalysis of diethylzinc addition. The reaction is highly enantioselective for some aromatic aldehydes and enantiomeric excess up to 99% was obtained.

Keywords: d; -Glucosamine; Diethylzinc; Titanium tetraisopropoxide; Enantioselective; Trifluoromethylsulfonamide

Solvent-free selective oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide over U₃O₈-supported nano-gold catalysts by Vasant R. Choudhary; Deepa K. Dumbre (pp. 252-257).

Influence of calcination temperature of Au (8wt%)/U₃O₈ (HDP) on its performance. Liquid-phase selective oxidation of benzyl alcohol to benzaldehyde with very high productivity and yield in the absence of solvent can be accomplished by using a reusable U₃O₈-supported nano-gold catalyst. The influences of catalyst parameters (method of gold deposition, gold loading, calcination temperature) and reaction conditions [reaction time, temperature] on the process performance have been thoroughly investigated.Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide over different uranium oxide supported nano-gold catalysts in the absence of a solvent has been thoroughly investigated. The influences of catalyst parameters [viz. method of gold deposition (impregnation, co-precipitation, deposition–precipitation and homogeneous deposition–precipitation), gold loading (0–8wt%) and catalyst calcination temperature (100–900°C)] on the catalyst performance have been investigated. The influence of reaction conditions [viz. reaction time (0–2h) and temperature (25–94°C)] on the process performance has also been studied. The Au/U₃O₈ catalyst prepared by the homogeneous deposition–precipitation and calcined at 400°C showed very high activity (100% benzyl alcohol conversion with >85% selectivity for benzaldehyde) in the process for a short reaction period (0.5h) at 94°C. The catalyst also showed excellent reusability in the process.

Keywords: Benzyl alcohol; Benzaldehyde; Partial oxidation; Au/U; ₃; O; ₈; catalyst; tert; -Butyl hydroperoxide; Nano-gold

Precipitable silver compound catalysts for the selective catalytic reduction of NOx by ethanol by Hong He; Yi Li; Xiuli Zhang; Yunbo Yu; Changbin Zhang (pp. 258-264).

Using the precipitable silver compounds greatly facilitates the preparation of monolith Ag/Al₂O₃ catalyst. AgCl was highly crystalloid on Al₂O₃, however, AgCl/Al₂O₃ gave the highest catalytic TOF for NOx reduction among the four catalysts. Calculated Mulliken charges of Ag compounds support the TOF results. The activity test and characterization results confirm that Ag⁺ is the active silver species for NOx reduction.The Ag/Al₂O₃, Ag₃PO₄/Al₂O₃, Ag₂SO₄/Al₂O₃ and AgCl/Al₂O₃ catalysts showed high activities for the selective catalytic reduction (SCR) of NOx by ethanol. AgCl was highly crystalloid on Al₂O₃, however, AgCl/Al₂O₃ gave the highest catalytic turnover frequency (TOF) for NOx reduction among the four catalysts. Calculated Mulliken charges of Ag compounds support the TOF results. The activity test and characterization results confirm that Ag⁺ is the active silver species for NOx reduction. The in situ FT-IR results of Ag₃PO₄/Al₂O₃, Ag₂SO₄/Al₂O₃ and AgCl/Al₂O₃ for NOx reduction further reveal a positive correlation between the high dispersion of Ag⁺ and the formation of active intermediates (the enolic and –NCO species), indicating a similar reaction pathway to that of the ethanol-SCR over Ag/Al₂O₃. Using the precipitable silver compounds greatly facilitates the preparation of monolith Ag/Al₂O₃ catalyst for practical usage. In fact, the high performance of the AgCl/Al₂O₃ honeycomb catalyst was confirmed by heavy duty diesel engine bench tests.

Keywords: NOx; Selective catalytic reduction; Ag species; Silver compound catalysts; Precipitator

High catalytic activity and selectivity for hydroxylation of benzene to phenol over multi-walled carbon nanotubes supported Fe₃O₄ catalyst by Shaoqing Song; Hongxiao Yang; Richuan Rao; Huade Liu; Aimin Zhang (pp. 265-271).

Multi-walled carbon nanotubes (MWCNTs), active carbon, graphite carbon, γ-Al₂O₃ and other porous materials supported iron were prepared for catalyzing the hydroxylation of benzene to phenol in the presence of H₂O₂. Fe/MWCNTs presents the highest conversion of benzene as well as the best selectivity to phenol, which should come from the formation of highly efficient catalytic components of Fe₃O₄ and the consumption of excessiveOH by MWCNTs.Multi-walled carbon nanotubes supported Fe₃O₄ catalysts (Fe/MWCNTs) were prepared for catalyzing the hydroxylation of benzene in the presence of hydrogen peroxide. The iron species in Fe/MWCNTs is Fe₃O₄ due to the spontaneous reduction of partial Fe³⁺ on the defect sites of multi-walled carbon nanotubes (MWCNTs), which is different from the Fe₂O₃ in the active carbon supported iron (Fe/AC) and graphitic carbon supported iron (Fe/GC) catalysts prepared by the same procedure. The benzene conversion was enhanced by 3.5 and 5.4 times, and the selectivity to phenol was increased by 2.1 and 1.5 times over Fe/MWCNTs catalyst in reference to the latter two carbon-based catalysts. The high catalytic activity for Fe/MWCNTs catalyst mainly comes from the more efficient catalytic component of Fe₃O₄ and the beneficial topology of MWCNTs. The high selectivity to phenol should arise from the consumption of the excessive hydroxyl radicals by MWCNTs, hereby preventing the further oxidation of phenol. The catalytic performance of Fe/MWCNTs is also superior to other carbon-free support-based iron catalysts, such as Fe/γ-Al₂O₃, Fe/MCM-41, Fe/HY and Fe/HZSM-5. These results indicate the potential application of Fe/MWCNTs catalyst in the hydroxylation of benzene to phenol.

Keywords: Multi-walled carbon nanotubes; Fe; ₃; O; ₄; Defects; Hydroxylation of benzene; Phenol

CrO_x/ nano-Ce_0.60Zr_0.35Y_0.05O₂ catalysts that are highly selective for the oxidative dehydrogenation of isobutane to isobutene by Guozhi Wang; Hongxing Dai; Lei Zhang; Jiguang Deng; Caixin Liu; Hong He; Chak Tong Au (pp. 272-278).

Nanosized Ce_0.60Zr_0.35Y_0.05O₂ ( nano-CZY) solid solution with a particle size of 4–5nm and CrO_x/ nano-CZY catalysts were prepared. The 8wt% CrO_x/ nano-CZY catalyst performs the best, giving 93% isobutene selectivity and 10% isobutene yield at 540°C in isobutane oxidative dehydrogenation. Such an excellent performance is related to the good reducibility of CrO_x domains and the promotion of O₂ adsorption at oxygen vacancies of nano-CZY.Fluorite-type nanosized Ce_0.60Zr_0.35Y_0.05O₂ ( nano-CZY) solid solution catalysts that are relatively uniform in particle size (4–5nm) and y CrO_x/ nano-CZY ( y is the weight percentage of Cr₂O₃ ranging from 2 to 10wt%) catalysts were prepared by the ethylene glycol-assisted CTAB-templated co-precipitation and incipient wetness impregnation methods, respectively. The materials were characterized by a number of analytical techniques and their catalytic performance was evaluated for the oxidative dehydrogenation of isobutane. The y CrO_x/ nano-CZY catalysts show excellent activities, with the y=8wt% one performing the best (ca. 93% isobutene selectivity and ca. 10% isobutene yield at 540°C and 30,000mL/(g_cat h)). We conclude that the good reducibility of the highly dispersed CrO_x domains and the promotion of O₂ adsorption at oxygen vacancies of nano-CZY (for enhanced oxidation of the reduced catalyst) are responsible for the excellent performance of the 8wt% CrO_x/ nano-CZY catalyst.

Keywords: Ceria–zirconia–yttria solid solution; Nanoparticle; Supported chromia catalyst; Isobutane oxidative dehydrogenation

Methylation of naphthalene on MTW-type zeolites. Influence of template origin and substitution of Al by Ga by Wei Wu; Weiguo Wu; O.V. Kikhtyanin; Lingfei Li; A.V. Toktarev; A.B. Ayupov; J.F. Khabibulin; G.V. Echevsky; Juan Huang (pp. 279-288).

Four ZSM-12 zeolites: Al-TEA, Al-MTEA, Ga/Al-MTEA and Ga-MTEA were investigated in the methylation of naphthalene. It was found that the catalysts exhibit drastically different properties regarding the production of dimethylnaphthalenes. Their distribution differs from that of thermodynamic equilibrium to a great extent in all cases, but the mode of this difference varies for each of the studied samples. This is mainly attributed to a presence of secondary mesopores in Al-TEA, Ga/Al-MTEA and Ga-MTEA zeolites.Two templates, methyltriethylammonium bromide (MTEA) and tetraethylammonium bromide (TEA) were used to synthesize aluminosilicate ZSM-12 zeolites. Additionally, zeolites isomorphously substituted (partially or totally) by gallium were prepared with MTEA. Various techniques including XRD, scanning electron microscopy (SEM), N₂ adsorption, NH₃-TPD, Fourier transform infrared (FTIR) spectroscopy and MAS NMR were used to monitor the physico-chemical properties of these solids. Catalytic properties of the prepared zeolites were studied in the methylation of naphthalene. Higher conversion of naphthalene, higher content of 2,6-DMN among total DMNs and higher 2,6-/2,7-DMN ratio were observed on Al-TEA sample and on Ga-containing zeolites compared to Al-MTEA. The specific morphology of zeolite crystals and the presence of secondary mesopores were identified to be responsible for remarkable catalytic performance of MTW-type zeolites.

Keywords: ZSM-12 zeolite; Isomorphous substitution; Methylation; 2,6-Dimethylnaphthalene; Selectivity

Water-improved heterogeneous transfer hydrogenation using methanol as hydrogen donor over Pd-based catalyst by Yizhi Xiang; Xiaonian Li; Chunshan Lu; Lei Ma; Qunfeng Zhang (pp. 289-294).

Water can highly improve the hydrogen transfer from methanol to styrene or nitrobenzene through the quick conversion of formaldehyde into formic acid with water, and the occurrence of the CTH from formic acid as hydrogen donor leading to the formation of CO₂. Hence, the heterogeneous CTH of unsaturated organics using methanol as hydrogen donor is realized.The heterogeneous catalytic transfer hydrogenation (CTH) of styrene and nitrobenzene over Pd-based catalyst using methanol as hydrogen donor was investigated in a fixed-bed reactor. With the increase of the molar ratio of water to methanol from 0 to 1, the conversions of styrene and nitrobenzene are increased from 26.3% and 7.1% to 100% and 31.9%, respectively, and the selectivity of aniline is increased from 22.0 to 94.5mol%. The presence of water improves the hydrogen transfer from methanol to styrene or nitrobenzene through the quick reaction of water with formaldehyde, formed from the dehydrogenation of methanol, into formic acid, which is an excellent hydrogen donor for the CTH of unsaturated organics. In the presence of water, methanol is a better hydrogen donor than isopropanol, n-propanol and ethanol, because water cannot easily react with acetone, propionaldehyde, and acetaldehyde formed from isopropanol, n-propanol, and ethanol, respectively. Additionally, the hydrogen atom utilization of the methanol donor in the presence of water is higher than the other donors, hydrogen atom in a part of water can also be utilized for the reduction of unsaturated organics.

Keywords: Water; Transfer hydrogenation; Methanol; Heterogeneous catalysis

Nanoscale manganese oxide octahedral molecular sieves (OMS-2) as efficient photocatalysts in 2-propanol oxidation by Aparna Iyer; Hugo Galindo; Shanthakumar Sithambaram; Cecil King’ondu; Chun-Hu Chen; Steven L. Suib (pp. 295-302).

OMS-2 is used as a photocatalyst for the oxidation of 2-propanol to acetone. The photocatalytic activity of OMS-2 materials prepared by different synthesis procedures is compared. Significant differences were found in conversion using different morphologies of OMS-2 under same reaction conditions. The characterization of catalysts is done using TPD, UV–vis, AOS, XRD, BET and FE-SEM. Catalysts were characterized before and after reactions using XRD and FTIR.Crystalline tunnel structure cryptomelane type manganese oxides (OMS-2) have been studied as photocatalysts for the selective oxidation of 2-propanol to acetone. The reaction is carried out with visible light irradiation at room temperature. The activities of various K-OMS-2 and metal doped OMS-2 (M-OMS-2) catalysts prepared by different synthesis procedures have been evaluated. K-OMS-2 and M-OMS-2 (M=Fe, Ni) with nanorod morphology were the most active photocatalysts. Conversions obtained for these catalysts ranged from 50 to 15%. K-OMS-2 fibers gave only 5–6% conversion. All reactions gave 100% selectivity to acetone. The reusability of the K-OMS-2 catalyst was also tested. Characterization of K-OMS-2 catalysts was done using several techniques like temperature programmed desorption, UV–vis spectroscopy, average oxidation state analysis, XRD, BET and FE-SEM. As suggested by the photochemical and characterization data, synthesis methodology, morphology, mixed valency and the release of oxygen from the OMS-2 structure are important factors for the design of active OMS-2 photocatalysts. XRD and FTIR were also used to study structural changes in the catalyst after photolysis.

Keywords: Photocatalysis; Oxidation; Manganese oxide octahedral molecular sieves; Oxygen evolution

Inhibition of coking and CO poisoning of Pt catalysts by the formation of Au/Pt bimetallic surfaces by Hui Ren; Michael P. Humbert; Carl A. Menning; Jingguang G. Chen; Yuying Shu; Udayshankar G. Singh; Wu-Cheng Cheng (pp. 303-309).

Results from DFT modeling indicate that the formation of Au–Pt surface alloy reduces the biding energy of adsorbates, which should lead to a reduction in the extent of coke formation and CO poisoning on Pt. The reduction of coke formation is verified experimentally based on the decomposition of cyclohexene; the weakening of CO adsorption is confirmed based on the desorption temperatures of CO from Pt and Au–Pt surfaces.The surface of Pt catalysts can be deactivated or poisoned during catalytic and electrocatalytic processes because of its strong bonding to hydrocarbon intermediates and carbon monoxide (CO). In the current work we have evaluated whether the formation of an Au/Pt bimetallic surface alloy would improve the resistance to coking and CO poisoning, using a combination of density functional theory (DFT) modeling and temperature-programmed desorption (TPD) experiments. The DFT results indicated that the binding energies of adsorbates, such as atomic hydrogen and oxygen, were much weaker on Au/Pt surfaces in comparison to Pt. The CO desorption TPD revealed that the Au/Pt surface bonded CO more weakly than Pt, indicating that modifying Pt with Au could potentially help reduce CO poisoning. In addition, the decomposition and dehydrogenation of cyclohexene were used as probe reactions to compare the extent of carbon deposition on the Pt and Au–Pt surfaces. TPD results showed that the presence of Au on Pt promoted the selective dehydrogenation of cyclohexene to benzene. In addition, Auger electron spectroscopy (AES) measurements revealed that the Au/Pt bimetallic surfaces inhibited carbon deposition on the surface, suggesting that the Au/Pt bimetallic alloy could be potentially resistant to coking.

Keywords: Coking inhibition; CO poisoning; Pt; Au/Pt alloy; Cyclohexene

Bifunctional mesoporous organic–inorganic hybrid silica for combined one-step hydrogenation/esterification by Yang Tang; Shaojun Miao; Brent H. Shanks; Xiaoming Zheng (pp. 310-317).

Bifunctional mesoporous organic–inorganic hybrid silica catalysts with platinum and propylsulfonic acid groups (Pt/SBA15-PrSO₃H) were designed for combined one-step hydrogenation/esterification (OHE) using acetic acid and acetaldehyde as the model reagents.Bifunctional mesoporous organic–inorganic hybrid silicas with platinum and propylsulfonic acid group (Pt/SBA15-PrSO₃H) were synthesized and tested for the combined one-step hydrogenation/esterification (OHE) reaction, which was employed as a model reaction for catalytic upgrading of biomass-derived bio-oil. The model reagents used were acetic acid and acetaldehyde. Different catalyst synthesis procedures were investigated and compared by varying the functional group incorporation method, platinum loading, reducing agent, etc. The textural and chemical properties of the catalysts made by the different synthesis procedures were characterized and compared with reactivity results. The need to create the organic acid sites prior to platinum incorporation was demonstrated. The efficacy of the bifunctional catalyst system for combined hydrogenation/esterification was demonstrated. Interestingly, the bifunctional Pt/SBA15-PrSO₃H catalyst exhibited superior esterification activity with about twice the acetic acid turnover number relative to that with the monofunctional SBA15-PrSO₃H catalyst. By combining metallic Pt nanoparticles with strong acid sites, this bifunctional mesoporous hybrid catalyst improved OHE activity and, therefore, has potential for application in the catalytic upgrading of bio-oil.

Keywords: Bifunctional catalyst; Mesoporous organic–inorganic hybrid silica; Propylsulfonic acid; Platinum; One-step hydrogenation/esterification; Bio-oil; Catalytic upgrading

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Applied Catalysis A, General (v.375, #2)

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Applied Catalysis A, General (v.375, #2)