Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics,reducibility and catalytic activity

The influence of Pd on a Co–Pd/γ‐Al₂O₃ heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH₃ desorption is found to be less for Co–Pd/γ‐Al₂O₃ sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H₂‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al₂O₃ displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al₂O₃ catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.     

Fabrication of Palladium Membranes Supported on a Silicalite‐1 Zeolite‐Modified Alumina Tube for Hydrogen Separation

Thin palladium membranes were fabricated on macroporous α‐Al₂O₃ tubes by electroless plating. The silicalite‐1 (Sil‐1) zeolite serving as intermediate and diffusion barrier layer was introduced to modify the surface roughness and pore size of the porous substrate and prevent the atomic interdiffusions of the metal elements between Pd layer and the support. The Pd composite membranes were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and electron probe microanalysis (EPMA), revealing that morphology and structure of the Sil‐1 layer significantly influence the Pd membrane preparation. Single‐gas permeation tests were carried out with gas H₂ and N₂ to determine the permeation performance of the membranes. The resulting membrane exhibited long‐term stability under hydrogen permeation.     

Hydrogen Production from Partial Oxidation and Steam Reforming of N‐octane Over Alumina‐supported Ni and Ni‐Pd Catalysts

Hydrogen production by partial oxidation and steam reforming (POSR) of n‐octane was investigated over alumina‐supported Ni and Ni‐Pd catalysts. It showed that Ni‐Pd/Al₂O₃ had higher activity and hydrogen selectivity than the nickel catalyst under the experimental conditions, which indicated Ni‐Pd/Al₂O₃ could be an effective catalyst for the production of hydrogen from hydrocarbons.     

Size‐Dependent Catalytic Activity of Supported Palladium Nanoparticles for Aerobic Oxidation of Alcohols

Silica‐alumina (SiO₂‐Al₂O₃)‐supported palladium catalysts prepared by adsorption of the tetrachloropalladate anion (PdCl₄²⁻) followed by calcination and reduction with either hexanol or hydrogen were studied for the aerobic oxidation of alcohols. The mean size of the Pd particles over the SiO₂‐Al₂O₃ support was found to depend on the Si/Al ratio, and a decrease in the Si/Al ratio resulted in a decrease in the mean size of the Pd nanoparticles. By changing the Si/Al ratio, we obtained supported Pd nanoparticles with mean sizes ranging from 2.2 to 10 nm. The interaction between the Pd precursor and the support was proposed to play a key role in tuning the mean size of the Pd nanoparticles. The Pd/SiO₂‐Al₂O₃ catalyst with an appropriate mean size of Pd particles could catalyze the aerobic oxidation of various alcohols to the corresponding carbonyl compounds, and this catalyst was particularly efficient for the solvent‐free conversion of benzyl alcohol. The intrinsic turnover frequency per surface Pd atom depended significantly on the mean size of Pd particles and showed a maximum at a medium mean size (3.6–4.3 nm), revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported Pd nanoparticles was structure‐sensitive.     

Pd/Al2O3 composite hollow fibre membranes: Effect of substrate resistances on H2 permeation properties

Al₂O₃ hollow fibres with different asymmetric macrostructures, i.e. various thickness ratios between a finger-like layer and a sponge-like layer, have been prepared by a phase inversion/sintering technique. Such asymmetric hollow fibres are used as substrates on which Pd membrane is deposited directly by an electroless plating (ELP) technique without any pre-treatment on substrate surface. Influences of the substrate macrostructure on hydrogen permeation through the Pd/Al₂O₃ composite membranes have been investigated both experimentally and theoretically. The hydrogen permeation through the Pd/Al₂O₃ composite membranes was not only determined by the Pd membrane thickness, but also by the macrostructural parameters of the substrate, such as effective porosity, mean pore size and pore size distribution etc. The thinner the Pd membrane, the higher the effective porosity is required to alleviate the substrate effect on the hydrogen permeation. Also, the deviation of the pore size is suggested to be around 1.2 for the further improved hydrogen permeation through the composite hollow fibre membranes.     

Diffusion‐enhanced hierarchically macro‐mesoporous catalyst for selective hydrogenation of pyrolysis gasoline

A novel Pd/Al₂O₃ catalyst with the hierarchically macro‐mesoporous structure was prepared and applied to the selective hydrogenation of pyrolysis gasoline. The alumina support possessed a unique structure of hierarchical mesopores and macropores. The as‐prepared and calcined alumina were characterized by X‐ray diffraction, N₂ adsorption‐desorption, and scanning electron microscopy. It showed that the hierarchically porous structure of the alumina was well preserved after calcination at 1073 K, indicating high thermal stability. The 1073 K calcined alumina was impregnated with palladium metal and compared with a commercial catalyst without macrochannels. Both the catalytic activity and the hydrogenation selectivity of the novel Pd/Al₂O₃ catalyst were higher than those of the commercial Pd/Al₂O₃ catalyst. In addition, apparent reaction activation energies obtained with the novel catalyst for model pyrolysis gasoline were 46–81% higher than those with the commercial catalyst. The results adequately demonstrated the enhanced mass transfer characteristics of the novel macro‐mesostructured catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Thermal stability of palladium on ceria-doped alumina

Several palladium on alumina and ceria/alumina catalysts were prepared and oxidized in air between 400 and 1000°C. The metal dispersion was determined by hydrogen titration of adsorbed oxygen. Dispersions above 50% were maintained on 0.2% Pd/Al₂O₃ up to 900°C. Adding 5.0% ceria, or increasing the metal loading to 2.5%, greatly reduces the thermal stability of the palladium, such that the dispersion falls rapidly at 600°C. The rates of methane oxidation (moles of CO₂/g Pd h) at 250°C and 5% excess oxygen are nearly equal on 0.22–2.50% Pd/3.5–5.2% CeO₂/Al₂O₃, dispersion 14–42%, and 0.20–0.46% Pd/Al₂O₃, dispersion 59–86%, but are 10 to 20 times lower than the rate on 2.3% Pd/Al₂O₃, dispersion 11%. The lower rate of methane oxidation on ceria-promoted and highly dispersed palladium on alumina might be due to the conversion of the palladium into less active palladium oxide during reaction.     

Effect of method of preparation on activity of Pd/Al2O3 monolith catalysts

Pd/Al₂O₃ monolithic catalyst of different washcoat thicknesses were prepared by two methods and tested for the activity of hydrogenation of α‐methyl styrene. These catalysts were prepared by two methods; either the palladium was impregnated on γ‐alumina and this Pd/Al₂O₃ powder was used to prepare the slurry for washcoating (Cat 1) or γ‐alumina washcoating was followed by impregnation of palladium (Cat 2). The effect of slurry concentration, pH of the slurry, and addition of binders on the catalyst properties was investigated. The monolithic catalysts were characterised by determination of metal dispersion, surface area, scanning electron microscopy, and weight loss of washcoat during ultrasonication. Well‐adhered washcoats were obtained with slurry prepared using milled γ‐alumina, whereas the adhesion of the washcoat prepared using Pd/Al₂O₃ powders was very poor. Addition of binders significantly improved the adhesion of the washcoats prepared from Pd/Al₂O₃. Metal dispersion for Cat 2 decreased with washcoat loading but did not change with loading for Cat 1. The activity tests were conducted at different washcoat loadings and the productivity of the monolithic catalyst prepared in both methods has been compared.     

Kinetics of hydrogenation of 4‐chloro‐2‐nitrophenol catalyzed by Pt/carbon catalyst

Hydrogenation of 4‐chloro‐2‐nitrophenol (CNP) was carried out at moderate hydrogen pressures, 7–28 atm, and temperatures in the range 298–313 K using Pt/carbon and Pd/γ‐Al₂O₃ as catalysts in a stirred pressure reactor. Hydrogenation of CNP under the above conditions gave 4‐chloro‐2‐aminophenol (CAP). Dechlorination to form 2‐aminophenol and 2‐nitrophenol is observed when hydrogenation of CNP is carried out above 338 K, particularly with Pd/γ‐Al₂O₃ catalyst. Among the catalysts tested, 1%Pt/C was found to be an effective catalyst for the hydrogenation of CNP to form CAP, exclusively. To confirm the absence of gas–liquid mass transfer effects on the reaction, the effect of stirring speed (200–1000 rpm) and catalyst loading (0.02–0.16 g) on the initial reaction rate at maximum temperature 310 K and substrate concentration (0.25 mole) were thoroughly studied. The kinetics of hydrogenation of CNP carried out using 1%Pt/C indicated that the initial rates of hydrogenation had first order dependence with respect to substrate, catalyst and hydrogen pressure in the range of concentrations varied. From the Arrhenius plot of ln rate vs 1000/T, an apparent activation energy of 22 kJ mol^?1 was estimated. © 2001 Society of Chemical Industry     

Wet oxidation of bleach plant effluent: Effects of pH on the oxidation with or without a Pd/Al2O3 catalyst

Wet oxidation of acidic bleach plant effluent was carried out at 423K and 1.5 MPa in a slurry reactor. The influence of pH of the bleach plant effluent was evaluated for both catalytic and non-catalytic oxidation in the liquid phase. The stability of the heterogeneous catalysts was investigated by measuring the extent of metal leaching into the solution. The pH of wastewater solution was found to influence significantly both the rate of total organic carbon (TOC) removal and the stability of the Pd/Al₂O₃ catalyst. Leaching of palladium and alumina occurred mostly at pH 2 and pH 11 under experimental conditions. With Pd/Al₂O₃, comparable rates of TOC removal were obtained in the pH range of 5 to 9 without significant leaching of both palladium and alumina. No metal leaching was observed using the Pd-Pt/Al₂O₃ catalyst at an initial pH value of 7. Implications of these experimental results for designing a catalytic wet oxidation process are discussed. A novel approach has been proposed for the treatment of effluents from softwood Kraft pulp mills.     

Homogeneous/heterogeneous palladium based catalytic system for Heck reaction. The reversible transfer of palladium between solution and support

Pd(II)/Al₂O₃ and Pd(0)/Al₂O₃, containing 0.6% of palladium were characterized by EDX, SEM and XRD methods and used as catalysts of the Heck coupling of bromobenzene with butyl acrylate at 140 °C in molten [Bu₄N]Br salt. Monoarylated (trans-PhCH = CHC(O)OBu) (1) and diarylated (Ph₂C = CHC(O)OBu) (2) products were obtained in amounts dependent on kind of base present in the system (Scheme 1). During the reaction palladium was partially leached from the support forming [Bu₄N][PdBr₄] complex that catalyze Heck reaction or undergo readsorption on Al₂O₃. These soluble palladium complexes are partially reduced to Pd soluble nanoparticles which can also be anchored on Al₂O₃ giving active catalyst of Pd(0)/Al₂O₃ type. Reduction of Pd(II) to Pd(0) during catalytic process at the presence of bases (NaHCO₂, NaHCO₃, NaOAc, Cs₂CO₃) was studied by XPS method and the total reduction was observed in reactions of PdCl₂(PhCN)₂ with NaHCO₂ or with NaHCO₃ and [Bu₄N]Br. It was experimentally proved that heterogenized catalyst, Pd(0)/Al₂O₃, after oxidative addition of aryl halides, serve as a source of soluble palladium species and colloidal nanoparticles that are active as homogeneous catalysts.     

Basic Study of Adhesion of Several Alumina‐based Washcoats Deposited on Stainless Steel Microchannels

The adhesion of several washcoats deposited on stainless steel microchannels was investigated by performing a mechanical test (drop test) after application‐oriented tests, temperature cycling, and water exposure. For this study alumina washcoats (γ‐Al₂O₃) and washcoats of commercially available alumina‐based catalyst powders (Pt/Al₂O₃, Rh/Al₂O₃) were used. The deposited washcoats showed very good adhesion not only for fresh samples but also after the application‐oriented tests.     

Characterization of some perovskite oxides based on YBa2Cu3O7 − x in relation to their use in methanol production

The oxidized and weakly reducible perovskite oxide YBa₂Cu₃O_{7 − x} (YBCO) has been prepared as a catalyst, supported on γ‐Al₂O₃. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al₂O₃ or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al₂O₃. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C₂–C₄ hydrocarbons. However the YBCO/γ‐Al₂O₃ catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH₃OH production. © 2000 Society of Chemical Industry     

Low temperature complete combustion of methane over titania-modified alumina-supported palladium

Effects of titania on the catalytic property of Pd/Al₂O₃ towards methane combustion were examined. The results revealed that the catalytic activity of the Pd/Al₂O₃ catalyst was considerably improved by pre-coating the alumina support with titania at low temperature (below 700 °C). Hydrogen chemisorption and BET measurements revealed that the titania-modified alumina supports could modify the support characterization to achieve a high dispersion of palladium. Temperature-programmed reduction and temperature-programmed desorption study further demonstrated that the coating of Pd/Al₂O₃ catalysts with titania can weaken the bond strength of Pd-O and enhance their catalytic activity towards methane combustion at lower temperature.     

Millisecond catalytic reforming of monoaromatics over noble metals

The millisecond autothermal reforming of benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal‐based catalysts: Pt, Rh, Rh/γ‐Al₂O₃, Rh–Ce, and Rh–Ce/γ‐Al₂O₃, as a function of carbon‐to‐oxygen feed ratio. The Rh–Ce/γ‐Al₂O₃ catalyst exhibited the highest feedstock conversion as well as selectivities to both synthesis gas and hydrocarbon products (lowest selectivities to H₂O and CO₂). Experimental results demonstrate a high stability of aromatic rings within the reactor system. Benzene and toluene seem to react primarily heterogeneously, producing only syngas and combustion products. Ethylbenzene and cumene behaved similarly, with higher conversions than benzene and toluene, and high product selectivity to styrene, likely due to homogeneous reactions involving their alkyl groups. Styrene exhibited low conversions over Rh–Ce/γ‐Al₂O₃, emphasizing the stability of styrene in the reactor system. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Selective catalytic reduction by urea in a fluidized‐bed reactor

The selective catalytic reduction (SCR) of NO_x by urea as a reducing agent was carried out over fresh and sulfated CuO/γ‐Al₂O₃ catalysts in a fluidized‐bed reactor. The optimum temperature ranges for NO reduction on the fresh and sulfated CuO/γ‐Al₂O₃ catalysts were 300–350 °C and 400–450 °C, respectively. NO reduction with the sulfated CuO/γ‐Al₂O₃ catalyst was somewhat higher than that with the fresh CuO/γ‐Al₂O₃ catalyst. N₂O formation increased with increasing reaction temperature. Ammonia (NH₃) slip increased with increasing gas velocity and decreased with increasing reaction temperature. Copyright © 2003 Society of Chemical Industry     

钯复合膜的制备及其在氢气氮气分离中的应用

Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.     

Single‐stage Treatment in Selective Hydrogenation of Acetylene over CDS Type of Pd‐Ag/Al2O3 Catalyst

The (computer designed shape) CDS type of Pd‐Ag/Al₂O₃ catalyst in single‐stage reactor provides superior catalytic activity and selectivity of ethylene in comparison with those of existed two‐stage reactors packed with G‐58B catalyst under industrial operating conditions. In this research, the contents of palladium and silver of catalysts were analyzed by inductive coupling plasma (ICP). The X‐ray photoelectron spectroscopy (XPS) showed that Pd‐Ag alloy has been formed. Higher yield of ethylene may be interpreted by both geometric and electronic effect induced from silver metal. By means of Pyrolysis/GC/MS analysis of used catalysts, the components of carbonaceous deposits were found to be n‐alkenes, including n‐C8 ～ n‐C16 or n‐C18, which may result from oligomerization of acetylene.     

Hydrodechlorination of 1,1-Dichlorotetrafluoroethane on Supported Palladium Catalysts. A Static-Circulation Reactor Study

Supported palladium catalysts were studied in CF₃CFCl₂ hydrodechlorination at 100°C using a static-circulation system. In order to minimize catalyst's deactivation a large excess of hydrogen was employed (H₂/CF₃CFCl₂ ratio 54/1). In spite of this precaution significant inhibition of the process occurred, associated with blocking palladium surface by hydrogen chloride species. Differences in the catalytic behavior of alumina-supported and unsupported palladium are discussed. A mild dependence between the catalytic activity and Pd dispersion was found. The Pd/Al₂O₃ catalyst characterized by low metal dispersion was more active than highly dispersed catalysts, showing the overall activity and selectivity to CF₃CFH₂ comparable with those observed by other authors for palladium single crystals. It is speculated that the most active sites for hydrodechlorination are plane atoms, whereas low coordination sites (on edges and corners of metal crystallites) are less suitable.     

Surface modification of macroporous Al2O3 tubes with carbon-doped TiO2 intermediate layer and preparation of highly permeable palladium composite membranes for hydrogen separation

ABSTRACT

To prepare H₂-permeable palladium composite membranes, a novel carbon-doped microporous TiO₂ intermediate layer was introduced to modify the surface of macroporous Al₂O₃ substrates. The Pd/TiO₂–C/Al₂O₃ membrane was prepared via electroless plating, and thereafter, carbon residue in the intermediate layer was removed by calcination in air, yielding a Pd/TiO₂/Al₂O₃ membrane. Experimental results indicate that the carbon residue shrinks the pore size of the intermediate layer and facilitates a decrease of membrane defects. Additionally, carbon removal induces a higher effective membrane area at the permeate side, which enhances hydrogen permeability. Furthermore, the apparent activation energy (E_A) and stability of the as-prepared Pd/TiO₂/Al₂O₃ membrane were investigated.