Reductive dehydration of butanone to butane over Pt/γ-Al2O3 and HZSM-5

We show that butanone can be reacted to form n-butane in an isothermal reactor containing a 1 wt.% Pt/γ-Al₂O₃ and an HZSM-5 catalyst (total mass of 12–400 mg, Si/Al = 11.5) below 160 °C with up to 99% selectivity and 67% yield. The catalyst loading (12–400 mg) and temperature (100–250 °C) were varied to obtain primary products whose selectivities decreased with conversion and secondary/tertiary products whose selectivities increased with conversion. As conversion increased, the selectivities of butanol and butene decreased, showing the formation of butane from butanone through a series reaction pathway: butanone → 2-butanol → butene → butane. Butane selectivity increased as the temperature was increased from 100 to 200 °C when compared at similar conversions due to higher dehydration rates over the zeolite. Processing ketones at low temperatures over bifunctional catalysts may be an efficient means of obtaining high yields of stable paraffins from reactive oxygenates.     

SO2 Reactions over γ-Al2O3,Pt/γ-Al2O3,Sn/γ-Al2O3 and Pt–Sn/γ-Al2O3

Platinum and Platinum–tin bimetallic catalysts supported on alumina were prepared by co-impregnation of both metallic precursors on the support and used as catalysts for the oxidation of SO₂. Platinum dispersion was determined by means of H₂–O₂ titration. Tin addition (1 and 2 wt%) only slightly decreased the exposed platinum atoms suggesting that tin is mainly over the support. At temperatures lower than 300 °C, SO₂ did not react with oxygen. Nevertheless, when the temperature was increased, the SO₂ oxidation began. The ignition temperatures for SO₂ oxidation (taken at 50% conversion) were 345 °C for 1% Pt/Al₂O₃ and 520 °C for 1% Pt–2% Sn/Al₂O₃. The strong displacement on activity suggests that tin plays an important role as inhibitor of the SO₂ oxidation reaction.     

Strong improvement on CH4 oxidation over Pt/γ-Al2O3 catalysts

A very strong promotion effect of the presence of 1000 ppmV C₃H₈ in the reaction feed on CH₄–O₂ reaction was found over unsulfated 1%Pt/γ-Al₂O₃ catalyst. This promotion was further increased on pre-sulfated 1%Pt/γ-Al₂O₃. The promoting effect of pre-sulfation on the activity of 1%Pt/γ-Al₂O₃ for propane combustion results in a further improvement on methane combustion due to propane combustion heat which is generated at lower temperatures, activating methane combustion over pre-sulfated 1%Pt/γ-Al₂O₃ at even lower temperatures relative to unsulfated 1%Pt/γ-Al₂O₃. These results suggest that small amounts of propane in the gas feed during CH₄–O₂ reaction over a pre-sulfated Pt/γ-Al₂O₃ catalyst may eliminate methane emissions at low temperatures from lean-burn NGV exhausts without being deactivated by sulfur poisoning as Pd supported catalysts.     

Steam reforming of liquid petroleum gas over Mn-promoted Ni/γ-Al2O3 catalysts

Three different Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃, Mn-Ni/γ-Al₂O₃ and Ni/Mn/γ-Al₂O₃, were prepared and applied to the steam reforming of liquid petroleum gas (LPG) mainly composed of propane and butane. For comparison, Ni/γ-Al₂O₃ catalysts containing different amount of Ni were also examined. In the case of the Ni/γ-Al₂O₃ catalysts, 4.1 wt% Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. Among the various Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. It also exhibited a similar H₂ formation rate compared with Ni/γ-Al₂O₃. Several characterization techniques—N₂ adsorption/desorption, X-ray diffraction (XRD), CO chemisorptions, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and CHNS analysis—were employed to characterize the catalysts. The catalytic activity increased with increasing amount of chemisorbed CO for the Mn-promoted Ni/γ-Al₂O₃ catalysts. The highest proportion of Mn⁴⁺ species was observed for the most stable catalyst.     

Tuning product selectivity of CO2 hydrogenation by OH groups on Pt/γ-AlOOH and Pt/γ-Al2O3 catalysts

Herein, we explore how OH groups on Pt/γ-AlOOH and Pt/γ-Al₂O₃ catalysts affect CO₂ hydrogenation with H₂ at temperatures from 250°C to 400°C. OH groups are abundant on γ-AlOOH, but rare at Pt-(γ-AlOOH) interface which is the most favorable site for CO₂ conversion on Pt/γ-AlOOH. This makes CO₂ hydrogenation on Pt/γ-AlOOH form CO weakly bonding to γ-AlOOH, which prefers to desorption from Pt/γ-AlOOH rather than further conversion, thus enhancing CO production on Pt/γ-AlOOH. Different from Pt/γ-AlOOH, OH groups are abundant at Pt-(γ-Al₂O₃) interface which is the most favorable site for CO₂ conversion on Pt/γ-Al₂O₃. This promotes CO₂ hydrogenation on Pt/γ-Al₂O₃ to form CO strongly bonding to Pt, which prefers to further hydrogenation to CH₄, and thereby increases CH₄ selectivity on Pt/γ-Al₂O₃. Therefore, the OH groups at metal-support interface are crucial factor influencing product distribution, and must be considered seriously when fabricating catalysts.     

Macroporous Monolithic Pt/γ-Al2O3 and K–Pt/γ-Al2O3 Catalysts Used for Preferential Oxidation of CO

Macro-porous monolithic γ-Al₂O₃ was prepared by using macro-porous polystyrene monolith foam as the template and alumina sol as the precursor. Platinum and potassium were loaded on the support by impregnation method. TG, XRD, N₂ adsorption–desorption, SEM, TEM, and TPR techniques were used for catalysts characterization, and the catalytic performance of macro-porous monolithic Pt/γ-Al₂O₃ and K–Pt/γ-Al₂O₃ catalysts were tested in hydrogen-rich stream for CO preferential oxidation (CO-PROX). SEM images show that the macropores in the macro-porous monolithic γ-Al₂O₃ are interconnected with the pore size in the range of 10 to 50 μm, and the monoliths possess hierarchical macro-meso(micro)-porous structure. The macro-porous monolithic catalysts, although they are less active intrinsically than the particle ones, exhibit higher CO conversion and higher O₂ to CO oxidation selectivity than particle catalysts at high reaction temperatures, which is proposed to be owing to its hierarchical macro-meso(micro) -porous structure. Adding potassium lead to marked improvement of the catalytic performance, owing to intrinsic activity and platinum dispersion increase resulted from K-doping. CO in hydrogen-rich gases can be removed to 10 ppm over monolithic K–Pt/γ-Al₂O₃ by CO-PROX.     

Neopentane conversion over Pd/γ-Al2O3

X-ray diffraction showed that during high temperature reduction at 600°C, chlorine-free Pd/-Al₂O₃ undergoes partial transformation to a Pd-Al alloy, which confirms results of other studies [9]. This evolution appears to have a large effect on the catalytic behaviour in the reaction of neopentane with hydrogen: the selectivity towards isomerization increases from <20 up to 80%. At the same time, the activation energy drops from 60 to 22 kcal/mol. These changes can be reversed by oxidation at 500°C followed by reduction at 300°C. The presence of residual chlorine (ex-PdCl₂ precursor) appears to inhibit the Pd induced reduction of Al₂O₃ leading to Pd-Al alloy formation.     

Direct dehydrogenation of n-butane over Pt/Sn/M/γ-Al2O3 catalysts: Effect of third metal (M) addition

A series of Pt/Sn/M/γ-Al₂O₃ catalysts with different third metal (M = Zn, In, Y, Bi, and Ga) were prepared by a sequential impregnation method for use in the direct dehydrogenation of n-butane to n-butene and 1,3-butadiene. In the direct dehydrogenation of n-butane, Pt/Sn/Zn/γ-Al₂O₃ catalyst showed the best catalytic performance. Catalytic performance decreased in the order of Pt/Sn/Zn/γ-Al₂O₃ > Pt/Sn/In/γ-Al₂O₃ > Pt/Sn/γ-Al₂O₃ > Pt/Sn/Y/γ-Al₂O₃ > Pt/Sn/Bi/γ-Al₂O₃ > Pt/Sn/Ga/γ-Al₂O₃. The catalytic performance increased with increasing metal–support interaction and Pt surface area of the catalyst.     

Glycerol steam reforming over Ni/γ-Al2O3 catalysts modified by metal oxides

The metal oxides modified Ni/γ-Al₂O₃ catalysts for glycerol steam reforming were prepared by impregnation. Characterization results of fresh catalysts indicated that the molybdates modification abated the acidity and the stronger metal-support interaction of Ni/γ-Al₂O₃ catalysts, leading to a stable catalytic activity. Especially, NiMoLa-CaMg/γ-Al₂O₃ (NiMoLa/CMA) catalyst exhibited no deactivation along with glycerol complete conversion to stable gaseous products containing 69% H₂, 20% CO and 10% CO₂ during time-on-stream of 42 h. TPO of spent Ni/γ-Al₂O₃ catalysts modified by different components showed that the carbon deposit on acidic sites and NiAl₂O₄ species led to catalysts deactivation. A lower reforming temperature and a higher LHSV and glycerol content were helpful to the production of syngas from GSR over NiMoLa/CMA; the reverse conditions would improve the formation of H₂.     

Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/-Al₂O₃ catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/-Al₂O₃ composite oxides and Pd-La/-Al₂O₃ catalysts show that Pd catalyzes the solid state reaction between A1₂O₃ and Al₂O₃ to form LaAlO₃. TPRd studies conducted on Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaAlO₃, and Pd-La/-Al₂O₃ catalysts suggest that Pd in the Pd-La/-Al₂O₃ catalyst interacts more strongly with LaAlO₃ than with -Al₂O₃. Reaction studies were conducted to investigate the activity of Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaA10₃, and Pd-La/-Al₂O₃ catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO₃ catalysts are most active for NO removal at stoichiometric and under net reducing conditions.     

Gas-phase hydrogenation of maleic anhydride to butyric acid over Cu/TiO2/γ-Al2O3 catalyst promoted by Pd

The promoter effect of palladium on the Cu/TiO₂/γ-Al₂O₃ catalyst was investigated for the gas-phase selective hydrogenation of maleic anhydride to butyric acid at atmospheric pressure. The results show that Pd is added rarely into the Cu/TiO₂/γ-Al₂O₃ catalyst for the hydrogenation of maleic anhydride, the higher selectivity to butyric acid can be obtained. In the absence of Pd (or Cu) in the Cu–Pd/TiO₂/γ-Al₂O₃ catalyst, the selectivity to butyric acid (BA) is nearly zero. Using the Cu–Pd/TiO₂/γ-Al₂O₃ (Pd/Cu=3/100 (atom)) catalyst, 56.2% selectivity to BA and 100% conversion of maleic anhydride were obtained at 280 °C.     

Lean NOxCatalysis over Sn/γ-Al2O3Catalysts

Sn/γ-Al₂O₃were effective and highly stable catalysts for NO reduction with propene under high partial pressures of oxygen and water. The activity depended on the Sn loading. For a 10 wt% Sn/Al₂O₃at 475–500°C, 58% conversion of 1000 ppm NO to N₂was obtained in the presence of 10% water and 15% O₂, at a space velocity of 30,000 h⁻¹, and 77% conversion at 15,000 h⁻¹. The NO conversion increased with O₂partial pressure but was suppressed by water below 500°C. The activity was also suppressed by SO₂but could be restored slowly after the removal of SO₂.     

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrO_y (17.5 wt%)-CeO₂ (X wt%)/γ-Al₂O₃ catalysts (X=0, 0.5, 2, 5, 8) with various Ce contents were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550℃ and 0.1 MPa. The prepared catalysts were characterized by BET, H₂-TPR, O₂-TPD, XPS, XRD, SEM-EDS and Raman spectroscopy. Among the prepared catalysts, the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen. The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts. The CeO₂ layer could inhibit the evolution of lattice oxygen (O^2-) to electrophilic oxygen species (O₂^-), and the oxygen defects on the catalyst surface were reduced. The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene, the average CO_x selectivity decreased from 24.41% (17.5Cr/Al) to 5.71% (17.5Cr-2Ce/Al), and the average propylene selectivity increased from 60.15% (17.5Cr/Al) to 85.05% (17.5Cr-2Ce/Al).     

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrO_y (17.5 wt%)-CeO₂ (X wt%)/γ-Al₂O₃ catalysts (X = 0, 0.5, 2, 5, 8) with various Ce contents were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550 °C and 0.1 MPa. The prepared catalysts were characterized by BET, H₂-TPR, O₂-TPD, XPS, XRD, SEM-EDS and Raman spectroscopy. Among the prepared catalysts, the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen. The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts. The CeO₂ layer could inhibit the evolution of lattice oxygen (O²⁻) to electrophilic oxygen species (O₂⁻), and the oxygen defects on the catalyst surface were reduced. The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene, the average CO_x selectivity decreased from 24.41% (17.5Cr/Al) to 5.71% (17.5Cr-2Ce/Al), and the average propylene selectivity increased from 60.15% (17.5Cr/Al) to 85.05% (17.5Cr-2Ce/Al).     

Stability of Pt/γ-Al2O3 Catalysts in Model Biomass Solutions

The stability of a Pt/??-Al₂O₃ catalyst in liquid water and aqueous solutions of 5?wt% glycerol or sorbitol at 225?°C is examined using a variety of physicochemical methods. It is demonstrated that the presence of glycerol and sorbitol significantly reduces the hydration of ??-Al₂O₃ to form boehmite as compared to treatment in pure water. The stability against hydration increases with increasing carbon chain length. Treatment with polyol solutions also results in reduced agglomeration of supported metal particles. The prevention of boehmite formation and agglomeration of metal particles are attributed to the formation of carbonaceous species on the surface. In addition to these effects, the deposits block a considerable portion of active metal surface area. IR spectroscopic analysis indicates that dehydration reactions play an important role in the formation of the carbonaceous deposits. The present results illustrate that water and dissolved biomass compounds can strongly affect the stability of heterogeneous catalysts under reaction conditions.     

Redispersion effects of citric acid on CoMo/γ-Al2O3 hydrodesulfurization catalysts

Calcined CoMo/γ-Al₂O₃ catalysts were modified by citric acid (CA) with different CA/Co ratios and the corresponding structure evolutions were systematically characterized. Then combined with HDS activity results, potential redispersion effects of CA were suggested: (i) weaken the MoO₃-Al₂O₃ interaction via competitive interacting with the OH groups of alumina surface to realize the redispersion of Mo oxides; (ii) transform tetrahedral MoO₄^2 − or β-CoMoO₄ into octahedral polymolybdate species and promote bulk MoO₃ to form well-dispersed MoO₃; (iii) remove the CoAl₂O₄-like species. These effects probably together promote the resulting sulfided catalysts with more type II CoMoS active sites, thus enhancing the HDS activity.     

Partial oxidation of methane to synthesis gas over α-Al2O3-supported bimetallic Pt–Co catalysts

The partial oxidation of methane to synthesis gas was studied at atmospheric pressure and in the temperature range of 550–800°C over -Al₂O₃-supported bimetallic Pt–Co, and monometallic Pt and Co catalysts, respectively. Both methane conversion and CO selectivity over a bimetallic Pt_0.5Co₁ catalyst were higher than those over monometallic Pt_0.5 and Co₁ catalysts. Furthermore, the addition of platinum in Pt–Co bimetallic catalysts effectively improved their resistance to carbon deposition with no coking occurring on Pt_0.5Co₁ during 80 h reaction. The FTIR study of CO adsorption observed only linearly bonded CO on bimetallic Pt–Co catalysts. TPR and XPS showed enhanced formation of a cobalt surface phase (CSP) in bimetallic Pt–Co catalysts. The origins of the good coking resistivity of bimetallic Pt–Co catalysts were discussed.     

Mechanism of the hydrodenitrogenation of o-toluidine and methylcyclohexylamine over NiMo/γ-Al2O3

The hydrodenitrogenation (HDN) of o-toluidine and its reaction intermediates was studied over a NiMo/γ-Al₂O₃ catalyst. The kinetics of the HDN of methylcyclohexylamine and of the hydrogenation of cyclohexene were also studied. Hydrogenation of o-toluidine alone produces methylcyclohexene and methylcyclohexane. When a sufficient quantity of cyclohexene is added during the HDN of toluidine, methylcyclohexylamine, the first intermediate in the hydrogenation of toluidine, becomes detectable. Because of its strong adsorption constant and high rate constant for reacting further to methylcyclohexene and methylcyclohexane, methylcyclohexylamine is not observed in the HDN of toluidine. Adding cyclohexene decreases the adsorption of methylcyclohexylamine, thus enabling its detection. The rate and adsorption constants of methylcyclohexylamine and cyclohexene in the HDN of methylcyclohexylamine were calculated by fitting the kinetic data to a Langmuir–Hinshelwood equation. A two-site model was used to describe the surface reactions, with one site for the methylcyclohexylamine reactions and the other for the cyclohexene reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetics of the Steady-State Acetylene Oxidation by Oxygen over a Pt/Rh/CeO2/γ-Al2O3 Three-Way Catalyst

The steady-state kinetics of acetylene oxidation has been studied in the framework of automotive exhaust gas catalysis over a commercially available three-way catalyst. Experiments under cold-start conditions have been carried out in a laboratory fixed-bed reactor, which can adequately be described by the developed elementary step model and rate parameters.     

Catalytic Oxygen Removal from Synthetic Coke Oven Gas: A Comparison of Sulfided CoMo/γ-Al2O3 and NiMo/γ-Al2O3 Catalysts with Pt/γ-Al2O3 as Benchmark Catalyst

For the oxygen removal from coke oven gas (COG) the catalytic activity of commercial catalysts CoMo/γ-Al₂O₃ and NiMo/γ-Al₂O₃ was evaluated after a sulfidation pretreatment and compared to the Pt/γ-Al₂O₃ reference catalyst. Elemental analysis and temperature-programmed desorption showed that the oxidation reaction and the associated oxidation of active sulfidic centers is the main cause of deactivation despite the presence of other reductants, such as hydrogen. This approach could allow an appropriate sulfide catalyst to be designed for oxygen removal corresponding to the typical COG composition in the presence of H₂S.