Palladium-containing Zeolites Research Articles

Modeling n-Pentane Hydroisomerization over a TsVM-Type Palladium-Containing Zeolite Catalyst

Two methods to form the active surface of TsVM-type palladium-containing zeolite catalysts are studied. The substance of the active sites of these catalysts is palladium, which is introduced into TsVM-type zeolite by impregnation or ion exchange. Catalyst samples are tested in the n-pentane hydroisomerization reaction. A step mechanism of n-pentane hydroisomerization over palladium-containing zeolite is proposed, and its corresponding kinetic model is constructed. Kinetic experiments are carried out in a flow reactor with a 200-cm3 reaction zone. The pressure in the reactor varies from 10 to 30 atm, the temperature from 553 to 633 K, the hydrogen-to-(n-pentane + isopentane) molar ratio from 2 to 6, and the contact time from 0.05 to 2.0 h. The constants of the kinetic model, the variances of estimates of the constants, the variances of responses, the variances of observations, and the repeatability error variances are estimated by the maximum likelihood method from the results of the sequentially designed experiment. A precision kinetic model of n-pentane hydroisomerization over a TsVM-type palladium-containing zeolite catalyst has been built.

Influence of clay binder on the liquid phase hydroisomerization of n-octane over palladium-containing zeolite catalysts

The influence of the clay binder on the properties and performance of palladium-containing zeolite catalysts in the liquid phase hydroisomerization of n-octane was studied. Three different framework zeolites with similar Si/Al ratio were used as catalysts: USY, mordenite and beta with or without binder. In all cases, a decrease in the catalytic activity of agglomerated samples, because of the modification of the acidity and the porosity of the zeolites by the binder, was observed. The decrease in the acidity after the agglomeration could be attributed to solid-state ion exchange between zeolite protons and clay sodium during the calcination of the catalyst. Moreover, the aluminium extraframework species (EFAL) created during the agglomeration process could cause a partial blocking of the micro-pore mouths, which would lead to an increase in the length of the effective diffusional pathway. After the agglomeration process, the monobranched isomers selectivity increased for all the samples while the multibranched isomers selectivity decreased. Due to the high pressure in the liquid phase, a significantly higher isomers selectivity was obtained as compared to vapour-phase conditions, and cracking became important only at relatively high average conversions.

Influence of the Binder on the n-Octane Hydroisomerization over Palladium-Containing Zeolite Catalysts

The influence of the binder on the properties and performance of palladium-containing zeolite catalysts in the n-octane hydroisomerization was studied. Three different framework zeolites were used as catalysts: mordenite, β, and ZSM-5 with or without binder. To characterize the catalysts, surface area measurements, temperature-programmed desorption of ammonia, atomic absorption spectroscopy, inductively coupled plasma emission spectrophotometry, hydrogen chemisorption, and solid-state 27Al NMR were used. Catalytic performance of the zeolites was strongly influenced by the binder because its presence modified both zeolite acidity and porosity. A decrease in the strong acidity of the zeolites could be observed when the samples were agglomerated, due to a solid-state ion exchange between the zeolite protons and bentonite sodium. The neutralization of some zeolite acid sites caused a decrease in the n-octane conversion for mordenite (from 90.5 to 53.8 mol %) and ZSM-5 (from 78.4 to 71.2 mol %) zeolites. The binder modified the porosity of the zeolite providing meso- and macropores, which allow a higher formation of branched isomers for mordenite (from 27.3 to 48.9 mol %) and ZSM-5 (from 14.3 to 35.4 mol %). Activity of β zeolite was modified by the presence of extraframework aluminum species (EFAL) formed during the agglomeration process, improving both n-octane conversion (from 22.9 to 88.7 mol %) and branched isomer selectivity (from 48.7 to 77.5 mol %).

Supercritical CO 2 as a superior solvent for the cyclization of diallylmalonate catalyzed by palladium-containing zeolites

Palladium-containing zeolites catalyze the cycloisomerization of diethyl diallylmalonate to dimethylcyclopentenes. When the reaction is carried out in toluene, the performance of the palladium catalyst depends on the pore size of the zeolites. At 60 °C, palladium adsorbed on large pore size Beta zeolite (pore size ∼7.4 Å) is more active than medium pore size ZSM-5 (pore size ∼5.4 Å). This lower activity of ZSM-5 compared to Beta is attributable to the restricted diffusion of reagent and products through the ZSM-5 channels as compared to Beta zeolite. However, due to the gas-like diffusion characteristic of the supercritical state, the activity of ZSM-5 increases and becomes identical to that of Beta zeolite using supercritical CO 2 as medium.

Controlling the softness–hardness of Pd by strong metal–zeolite interaction: cyclisation of diallylmalonate as a test reaction

The cycloisomerisation of diallylmalonate to form cyclopentenes is demonstrated here to be a specific test reaction for hard Lewis acid sites in palladium-containing zeolites. We have found a correlation of the cycloisomerisation efficiency for a series of palladium-supported zeolites with the hardness of their framework as previously reported by quantum chemical calculations. Thus, the catalytic activity decreases and eventually disappears when the softness of the zeolite framework increases, the optimum in the activity being achieved when palladium is hosted in hard zeolite frameworks. In this way, the cycloisomerisation yield decreases in the series HY (Si/Al 15)≈HBeta (Si/Al 12.5)>HZSM-5 (Si/Al 15)>(Si)Beta (Si/Al ∞)>H,NaBeta (Si/Al 12.5)>HNaY (Si/Al 2.6)>NaY (Si/Al 2.6)>NaBeta (Si/Al 12.5)≈(Si,Ge)Beta.

Controlling the softness?hardness of Pd by strong metal?zeolite interaction: cyclisation of diallylmalonate as a test reaction

The cycloisomerisation of diallylmalonate to form cyclopentenes is demonstrated here to be a specific test reaction for hard Lewis acid sites in palladium-containing zeolites. We have found a correlation of the cycloisomerisation efficiency for a series of palladium-supported zeolites with the hardness of their framework as previously reported by quantum chemical calculations. Thus, the catalytic activity decreases and eventually disappears when the softness of the zeolite framework increases, the optimum in the activity being achieved when palladium is hosted in hard zeolite frameworks. In this way, the cycloisomerisation yield decreases in the series HY (Si/Al 15)≈HBeta (Si/Al 12.5)>HZSM-5 (Si/Al 15)>(Si)Beta (Si/Al ∞)>H,NaBeta (Si/Al 12.5)>HNaY (Si/Al 2.6)>NaY (Si/Al 2.6)>NaBeta (Si/Al 12.5)≈(Si,Ge)Beta.

Palladium-Containing Zeolite Beta Macrostructures Prepared by Resin Macrotemplating

A multistep procedure for the preparation of palladium-containing zeolite beta spheres using anion-exchange resin beads as shape-directing macrotemplates is presented. In a first step, resin beads ...

Influence of carrier acidity on activity of palladium-containing zeolite catalysts in CO oxidation

Activity of palladium Y-zeolite catalysts having various decationization states has been studied in CO oxidation. IR spectroscopic data for chemisorbed CO molecules indicate changes in the electronic state of palladium in the samples. Activity of the catalysts in CO oxidation decreases with increasing carrier acidity and electron deficiency of palladium.

Selective oxidation of carbon monoxide in the presence of butane and maleic anhydride

The selective oxidation of carbon monoxide in the presence of butane and maleic anhydride has been studied over platinum- and palladium-containing zeolites as well as palladium-on-silica (Pd/SiO 2 catalysts. The results show that although a zeolite support is needed in many systems to effect a kinetic control to improve selectivity, thermodynamic control using Pd(∼2–4ppm) SiO 2 is sufficient to give the desired selectivities in this system. In addition, a palladium-containing vanadium-phosphate catalyst was prepared that showed complete oxidation of carbon monoxide, conversion of butane to maleic anhydride, and no observable decomposition of the maleic anhydride.

A study by X-ray spectral and other physical methods of the mechanism of the poisoning of Y-zeolites by thiophene in the hydrogenation of n-hexene

The aim of the present work was to study the possibilities provided by XRS in the study of catalytic processes for the case of the hydrogenation ofhex-l-ene on palladium-containing zeolites in the presence of thiophene. This catalytic system was chosen for a number of reas'ons. Firstly, the study of this system is of interest because the reaction with sulfurcontaining compounds is considered to be one of the principal causes of the poisoning of petroleum-processing catalysts. Secondly, from available data on the x-ray spectra of organic molecules and their complexes with metals, it was expected that XRS might be most effectively used to study processes involving sulfur-containing compounds. It may be noted that the hydrogenation of n-hexene in the presence of thiophene has previously been used many times as a model process in the study of the mechanism of the poisoning of zeolite catalysts by sulfur, and has been characterized chemically in considerable detail [9]. In addition to XRS, we also used radiospectroscopic and diffuse reflectance methods.

Deuterium exchange with the surface hydrogen of zeolite catalysts 5. Palladium-containing zeolites

1. The rate of D2 exchange with the OH groups of a 0.70 HNaY zeolite can be increased by bringing the latter into mechanical contact with a Pd-containing zeolite. Surface migration of the activated deuterium is the limiting step in the heteroexchange. 2. The coefficient of surface migration of the activated deuterium is at least three orders higher than the coefficient of diffusion of OH group protons.

Catalytic activity of palladium-containing zeolites in the complete oxidation of benzene

The dependence of palladium distribution in zeolites on the temperature of thermal treatment has been established from the data on oxygen chemisorption and the statistical processing of electron micrographs. The influence of palladium distribution in zeolites on their catalytic activity towards the complete oxidation of benzene has been shown.