Conversion of methylcyclopentane (MCP) on Pt/MoO2, Ir/MoO2 and Pt–Ir/MoO2 catalysts

The effect of the metal and reaction temperature was investigated in the conversion of MCP with hydrogen at atmospheric pressure. The highly dispersed 0.5 wt.% Pt/MoO₂, 0.5 wt.% Ir/MoO₂ and 0.25 wt.%–0.25 wt.% Pt–It/MoO₂ metal catalysts were prepared by incipient wetness impregnation or co-impregnation methods. The most active catalyst in the conversion of MCP was Pt/MoO₂ and the most selective to MCP ring opening was Ir/MoO₂. At low temperature, Ir/MoO₂ opened the MCP ring at the secondary–secondary position. High temperature promoted ring opening at the secondary–tertiary positions, which was attributed to the adlineation sites. At low temperatures, Pt/MoO₂ and Pt–Ir/MoO₂ promoted only the ring enlargement reaction while Ir/MoO₂ promoted both ring opening and ring enlargement. Ring enlargement of MCP to cyclohexane and benzene was catalysed by electron deficient adduct sites, while ring opening to 2-meythylpentane (2-MP), 3-methylpentane (3-MP) and n-hexane (n-H) was catalysed by metallic sites. At high temperatures, MCP broken into C₁–C₅ fragments and deactivation of the catalysts was observed. The Ir/MoO₂ showed the highest selectivity for cracking. The differences in selectivity were attributed to the presence of adsorbed agostic species, where the electronic environment of Ir and Pt are different.     

Vapor-Phase Dehydration of 1,3-butanediol over CeO2–ZrO2 Catalysts

The dehydration of 1,3-butanediol was investigated over CeO₂–ZrO₂ catalysts prepared by impregnation at temperatures of 325–375 °C. Pure CeO₂ selectively catalyzed the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol, while pure ZrO₂, which was less active than pure CeO₂, catalyzed the dehydration to 3-buten-1-ol. In the CeO₂/ZrO₂ catalyst in which CeO₂ was supported on zirconia, the presence of a small amount of CeO₂ suppressed the formation of 3-buten-1-ol and induced the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol and the subsequent dehydrogenation of 3-buten-2-ol to form 3-buten-2-one and butanone. The activity would be related to the redox features of CeO₂. The monoclinic phase of zirconia support decreased while the cubic CeO₂ phase increased as CeO₂ content was increased. In contrast, in the ZrO₂/CeO₂ catalyst in which ZrO₂ was supported on cubic CeO₂, only the cubic CeO₂ phase was observed and ZrO₂ species appeared in the form of a solid solution of CeO₂–ZrO₂ with fluorite structure. Regardless of zirconia loading, ZrO₂ species did not affect the catalytic activity of ZrO₂/CeO₂, which was controlled by CeO₂ species.     

Comparative Study on Partial Oxidation of Methane over Ni/ZrO2, Ni/CeO2 and Ni/Ce–ZrO2 Catalysts

The partial oxidation of methane has been studied by sequential pulse experiments with CH₄ O₂ CH₄ and simultaneous pulse reaction of CH₄/O₂ (2/1) over Ni/CeO₂, Ni/ZrO₂ and Ni/Ce–ZrO₂ catalysts. Over Ni/CeO₂, CH₄ dissociates on Ni and the resultant carbon species quickly migrate to the interface of Ni–CeO₂, and then react with lattice oxygen of CeO₂ to form CO. A synergistic effect between Ni and CeO₂ support contributes to CH₄ conversion. Over Ni/ZrO₂, CH₄ and O₂ are activated on the surface of metallic Ni, and then adsorbed carbon reacts with adsorbed oxygen to produce CO, which is composed of the main path for the partial oxidation of methane. The addition of ceria to zirconia enhances CH₄ dissociation and improves the carbon storage capacity. Moreover, it increases the storage capacity and mobility of oxygen in the catalyst, thus promoting carbon elimination.     

Selective Ring-Opening of Methylcyclopentane Over Titania-Supported Monometallic (Pt, Ir) and Bimetallic (Pt–Ir) Catalysts

An investigation of the selective ring-opening of methylcyclopentane (MCP) was conducted for the first time on Pt/TiO₂, Ir/TiO₂ and Pt?CIr/TiO₂ catalysts with low amounts of noble metals (0.5?wt%) over a temperature range of 180?C400?°C under hydrogen at atmospheric pressure. The catalysts were prepared by impregnation or co-impregnation and characterized by different physico-chemical techniques, including SEM, XRD, H₂-TPR, N₂-sorption, TEM and elemental analysis. The metallic particles were highly dispersed on the TiO₂ support at isodispersion of ~1?nm. The particles exhibited icosahedral Mackay structures limited by (111) planes. The catalytic results show that the activity in the MCP was strongly influenced by the intrinsic nature of the metal and by the temperature. The most active catalyst was Ir/TiO₂. The order of the reactivity as a function of the temperature and total conversion was Ir/TiO₂ 180?°C (???=?2?%)?>?Pt?CIr/TiO₂ 220?°C (???=?27.8?%)?>?Pt/TiO₂ 260?°C (???=?9.9?%). Under these conditions, all of the catalysts exhibited the ability to open the ring of MCP with an atom economy, without unwanted products of cracking and ring-enlargement reactions. The synergy between Pt?CIr bimetallic particles was assessed by the total conversion of MCP, whereas the ring-opening results indicated that the reaction took place on Ir sites. These results suggest that the bimetallic catalyst contained separate entities of two metals. Increased reaction temperatures led to reduced reaction selectivity with respect to ring-opening of MCP versus the cracking side reaction.     

Characterization and catalytic properties of MoO3–V2O5/Nb2O5 catalysts

The influence of molybdenum oxide on the dispersion of vanadium oxide supported on niobia was investigated. A series of MoO₃–V₂O₅/Nb₂O₅ catalysts with varying MoO₃ content ranging from 1% to 5% (w/w) with fixed V₂O₅ content were prepared by impregnation of previously prepared 5 wt% V₂O₅/Nb₂O₅ with requisite amounts of ammonium molybdate solution. X-ray diffraction patterns indicate the presence of β-(Nb,V)₂O₅ phase with the addition of MoO₃ up to a loading of 3 wt%. Temperature-programmed reduction (TPR) results suggest that the reducibility is decreasing with MoO₃ loading. The results of temperature programmed desorption (TPD) of ammonia suggest that the acidity of the catalysts increased with the addition of MoO₃. The catalytic properties of the catalysts in the ammoxidation of 3-picoline were correlated with the characterization data.     

Selective Production of H2 from Ethanol at Low Temperatures over Rh/ZrO2–CeO2 Catalysts

A series of Rh catalysts on various supports (Al₂O₃, MgAl₂O₄, ZrO₂, and ZrO₂–CeO₂) have been applied to H₂ production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO₂–CeO₂ > Rh/Al₂O₃ > Rh/MgAl₂O₄ > Rh/ZrO₂. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO₂–CeO₂ catalyst exhibits the highest CO₂ selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO₂–CeO₂ catalyst exhibited the highest H₂ yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO₂–CeO₂ resulting in efficient transfer of mobile oxygen species from the H₂O molecule to the reaction intermediate.     

Simultaneous dehydrogenation and isomerization of n-butane to isobutene over Cr/WO3–ZrO2 catalysts

A series of WO₃-promoted Cr₂O₃-based catalysts were prepared and tested for the simultaneous dehydrogenation and isomerization of n-butane to isobutene. It is found that a Cr₂O₃/WO₃–ZrO₂ system is an effective catalyst for this reaction; however, the catalytic behavior is dependent on Cr₂O₃ and WO₃ contents, space velocity and temperature. 10 wt% Cr₂O₃/20 wt% WO₃–ZrO₂ can give high initial conversion and isobutene selectivity, but it deactivates rapidly due to the variation of surface properties and pore structure caused by carbon deposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel MoO3/CeO2–ZrO2 catalyst for the selective catalytic reduction of NOx by NH3

A series of MoO₃-doped CeO₂–ZrO₂ catalysts were investigated for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). It was found that the added MoO₃ significantly enhanced the activity of CeO₂–ZrO₂ catalyst for NH₃-SCR of NO_x in a wide temperature range and the optimum MoO₃ loading is 5%. The highly dispersed MoO₃ not only resulted in more Lewis acid and Brønsted acid sites formed on the catalyst surface, but also increased the redox property of the catalyst, all of which account for the enhanced SCR activity.     

Propane Oxidative Dehydrogenation on V–Sb/ZrO2 Catalysts

The catalytic properties of V–Sb/ZrO₂ and bulk Sb/V catalysts for the oxidative dehydrogenation of propane were studied. Samples were characterized by nitrogen adsorption, temperature-programmed reduction, temperature-programmed pyridine desorption and photoelectron spectroscopic techniques. Vanadia promotes the transition of tetragonal to monoclinic zirconia and the formation of ZrV₂O₇. Surface V and Sb oxide species do not appear to interact among them below monolayer coverage, but SbVO4 forms above monolayer. Simultaneously the excess of antimony forms α-Sb₂O₄. Activity and selectivity show no dependence on the acidity of the catalysts. However, there is a strong dependence of activity/selectivity on composition; surface vanadium species are active for propane oxidative dehydrogenation and the presence of Sb, affording rutile VSbO₄ phase makes the system selective to C₃H₆, this is believed to be related to the redox cycle involving dispersed V⁵⁺ species and lattice reduced vanadium site in the rutile VSbO₄ phase.     

Hydrocracking of Athabasca bitumen over binary metal oxide (SiO2MoO3 and CoO/SiO2MoO3) catalysts

The hydrocracking of Athabasca bitumen was studied over SiO₂MoO₃ (80: 20wt%), 2.92 and 5.54 wt% CoO on SiO₂MoO₃, and commercially available CoOMoO₃/Al₂O₃ catalysts at temperatures in the range 648–698 K for 2 h under an initial hydrogen pressure of 7.0 M Pa in a batch reactor. The reaction products were separated into coke, asphaltenes, resins, aromatics, saturates and gases. The severity of cracking increased with increased reaction temperature. At 698 K, asphaltene and resin yields were low (0.59 and 13.22 wt%, respectively) and gas yields high (40.5 wt%). SiO₂MoO₃ and CoO/SiO₂MoO₃ catalysts showed higher activity than commercial CoOMoO₃/Al₂O₃ catalyst in the conversion of heavy fractions (asphaltenes and resins) and in the formation of light fractions (saturates and aromatics).     

Characterization of MoO3–V2O5/Al2O3 catalysts for selective catalytic reduction of NO by NH3

MoO₃–V₂O₅/Al₂O₃ catalysts were characterized by B.E.T., XRD, LRS, XPS and TPR and the effect of MoO₃ addition to alumina supported vanadia catalysts on the catalytic activity for the selective catalytic reduction of NO by ammonia was investigated. Upon the addition of MoO₃, catalytic activity was enhanced and the particle size of V₂O₅ which is shown by the results of B.E.T., XRD and Raman spectroscopy decreased. This was one reason for increased catalytic activity. The results obtained by XPS and TPR showed that MoO₃ addition to alumina supported vanadia catalysts increased the reducibility of vanadia and this was the another reason for synergy effect between MoO₃ and V₂O₅ in MoO₃–V₂O₅/Al₂O₃ catalysts.