Properties Of Palladium Catalysts Research Articles

Influence of Phosphorus Modifier and Nature of the Support on the Properties of Palladium Catalysts in the Chemoselective Hydrogenation of Acetylenic Compounds

Efficient heterogeneous catalysts for the chemoselective hydrogenation of terminal and disubstituted alkynes and alkynols to monoenes based on Pd–P particles have been proposed. The influence of a zeolite support (Na-ZSM-5, MCM-41) and a phosphorus modifier on the properties of palladium catalysts in the semihydrogenation of acetylenic compounds is considered. It has been shown that promotion with phosphorus increases the activity of palladium catalysts in the hydrogenation of various acetylenic compounds from 2.5 to 30 times without reducing the selectivity for monoenes. High selectivity for monoenes is determined by both thermodynamic and kinetic factors. Using the example of the acetylenic alcohol hydrogenation the possibility of changing the ratio of hydrogenation rates of triple and double bonds as a result of varying the solvent nature and the structural order of the catalyst particles was demonstrated.

Effects of Phosphorus Modifier and Support on the Properties of Palladium Catalysts in the Chemoselective Hydrogenation of Acetylenic Compounds

Effects of Phosphorus Modifier and Support on the Properties of Palladium Catalysts in the Chemoselective Hydrogenation of Acetylenic Compounds

Effect of a phosphorus modifier on the behavior of palladium catalysts in direct synthesis of hydrogen peroxide

The behavior of palladium-phosphorus catalysts deposited on a Na-ZSM-5 zeolite support, in the direct synthesis of hydrogen peroxide under mild conditions has been studied. It was found that elemental phosphorus exerts a promoting effect on the activity and selectivity of Pd catalysts for synthesizing H2O2. A direct relationship between the P:Pd ratio (in the range P:Pd = 0: 1.0) and the activity of the catalysts is shown. The influence of phosphorus on the properties of palladium catalysts in side reactions: decomposition and hydrogenation of H2O2 is considered. The chemical and phase composition of Pd-P particles was studied by ICP, HRTEM, electron diffraction, and XRD methods. The modifying effect of phosphorus on the properties of Pd catalysts in the direct synthesis of H2O2 is associated with the formation of solid solutions between palladium and phosphorus, an increase in the dispersion, and the surface roughness of Pd-P particles.

Palladium-Phosphorus Nanoparticles as Effective Catalysts of the Chemoselective Hydrogenation of Alkynols

The effect of the composition of the catalytic system and reaction conditions on the properties of phosphorus-modified palladium catalysts in hydrogenations of alkynols was studied. Modification with phosphorus increased the activity and turnover number of palladium catalysts in the hydrogenation of the model compound 2-methyl-3-butyn-2-ol (MBY) without any reduction in the selectivity to 2-methyl-3-butene-2-ol at 95–98% MBY conversion. The promoting effect of phosphorus on the properties of the palladium catalyst is caused not only by an increase in the particle size, but also, probably, by a change in the energy of interaction of reagents with the active sites. Hypotheses on the nature of the carriers of catalytic activity in Pd–P particles were discriminated using kinetic methods with the differential selectivity of catalytic systems as the main measured parameter under the conditions of competition between two alkynols. The hydrogenation of acetylenic alcohols involves only one of the two potentially active forms in Pd–P nanoparticles—Pd(0) clusters, whereas the hydrogenation of the resulting allyl alcohols involves both Pd(0) clusters and palladium phosphides.

The Effect of Particle Size and the Modifier on the Properties of Palladium Catalysts in the Synthesis of Hydrogen Peroxide by the Anthraquinone Method

The effect of the composition of the catalytic system and the size of particles on the properties of palladium catalysts in 2-ethyl-9,10-anthraquinone hydrogenation was studied. It was shown that, depending on the nature of a reducing agent (H2, AlEt3), palladium species formed in the absence of a modifying agent catalyze various side processes to a substantial extent together with 2-ethyl-9,10-anthraquinone hydrogenation: mostly hydrogenolysis (in the case of H2 as a reducing agent) and hydrogenation of aromatic rings in 2-ethyl-9,10-anthrahydroquinone (in the case of AlEt3 as a reducing agent). Elementary phosphorus was found to have a promoting effect on the selectivity of palladium catalysts in the synthesis of hydrogen peroxide by the anthraquinone method. The main factors that make it possible to control the selectivity of palladium catalysts were discussed.

Influence of CeO 2 and La 2O 3 on properties of palladium catalysts used for emission control of natural gas vehicles

Pd/YZ-Al 2O 3 (Y and Zr modified Al 2O 3, and hereafter, labelled as Al) catalysts with 4 wt% additive CeO 2 and/or La 2O 3 were prepared and characterized by X-ray photoelectron spectroscopy (XPS), NO-temperature programmed desorption (NO-TPD), N 2-adsorption/desorption (Brunauer-Emmet-Teller BET method), X-ray diffraction (XRD) and CO-chemisorption. Catalytic activities for CH 4, CO and NO conversion were tested in a gas mixture simulated the emissions from natural gas vehicles (NGVs) operated under stoichiometric conditions. The results indicated that all catalysts exhibited excellent catalytic performances for CH 4 and CO oxidation and the promoting effect of CeO 2 or La 2O 3 was significant for NO conversion. XPS results showed that the electron density around Pd was increased by CeO 2 and/or La 2O 3, the binding energy of Pd 3d decreased as the order: Pd/Al > Pd/Ce/Al > Pd/La/Al > Pd/CeLa/Al. The electron-rich Pd showed Rh-like catalytic properties which exhibited good activity for the reduction of NO. NO-TPD results showed that the addition of CeO 2 and/or La 2O 3 increased NO adsorption on surface, and promoted the conversion of NO.

Palladium catalysts deposited on silicon nitride in the deep oxidation of methane

The physicochemical and catalytic properties of palladium catalysts were studied in the deep oxidation of methane. The catalysts were deposited on silicon nitride from aqueous (Pd/Si3N4-a) and toluene (Pd/Si3N4-t) solutions of palladium acetate. The use of aqueous and organic solutions of palladium acetate, all other preparation conditions being equal, resulted in the formation of palladium systems with different catalytic properties. The sample from Pd/Si3N4-t was characterized by high activity and stability. The systems studied had different structures and adsorption properties of palladium nanoparticles, which influenced the form of reagent adsorption, catalytic properties, and mechanism of surface reactions. The suggestion was made that the solvent played a key role in the formation of the active surface of Pd-containing catalytic systems.

Properties of palladium catalysts on carbon supports prepared from chemically modified and activated anthracites

The influence of chemical modification and thermal activation on the porous structure of Donbass anthracites (Ukraine) and on the state and catalytic properties of supported palladium has been studied. The most regular distribution of supported palladium particles with an average size of about 2 nm was observed for the supports prepared from the chemically modified anthracites. The activity of supported palladium in the liquid-phase hydrogenation of cyclohexene varies more than 10-fold depending on the preparation method of the anthracite support. The catalysts with the palladium nanoparticles located in micropores of the carbon support exhibit a lower catalytic activity.

Texture and catalytic properties of palladium supported on thermally expanded natural graphite

Data about preparation and properties of palladium catalysts on porous supports prepared by intercalation and subsequent thermal expansion of natural graphite are presented. Some relations between the structure of the graphite support, the state of supported palladium and its catalytic properties in the model reaction of cyclohexene liquid-phase hydrogenation were established.

Catalysts based on fiberglass supports: V. Absorption and catalytic properties of palladium catalysts based on a leached silica-fiberglass support in the selective hydrogenation of an ethylene-acetylene mixture

The absorption and catalytic properties of palladium catalysts (0.01% Pd) based on leached soda–silica fiberglass supports were studied in the selective hydrogenation of acetylene as the constituent of an ethylene–acetylene mixture. It was found that fiberglass catalysts exhibited much higher selectivity than traditional supported Pd catalysts. It was suggested that the high selectivity in the reaction of acetylene hydrogenation resulted from the selective absorption (diffusion) of acetylene in the bulk of fiberglass, where Pd microparticles are localized.

The use of catalyzed decomposition of cupric formate for study of properties of palladium catalysts

The decomposition of cupric formate induced by palladium catalysts has been studied in aqueous solution. Effects of the carrier and the proper active component on the cupric formate concentration decrease have been separated. Kinetic data of the decomposition reaction have been obtained, and processes affecting the decomposition have been followed. The decomposition rates found with the use of various catalysts enabled to test the effects of preparation methods of palladium catalysts on their activity. The values found agree with hydrogenation activity of the catalysts.

Oxide-metal catalysts for the reforming of gasolines Communication 5. Some peculiar features of the catalytic and physical properties of palladium catalysts

1. The following catalysts for reforming gasoline were investigated: No. 1-Pd on A12O3, No. 2-Pd on A12O3 which had been treated with HP and No. 3-sulfided Pd on A12O3 which had been treated with HF. The specific surfaces of catalysts No. 1 and 2 were the same, but that of the sulfided catalyst No. 3 was less by a factor of 1.5. Only catalyst No. 2 sintered appreciably. 2. There were no other crystalline phases in the catalysts besides γ-Al2O3 and Pd; any PdS in the sulfided catalyst No. 3 could only be present in the amorphous state or in the form of a surface compound. The order of the specific activities of the catalysts was the same for the dehydrogenation of cyclohexane and the reforming of gasoline reactions. 3. The temperature coefficient of the reaction velocity was greater for catalyst No. 3 than for No. 1 and 2. This explains the greater activity of catalyst No. 3 under gasoline reforming conditions. 4. It is suggested that the increased activity and stability of catalyst No. 3 was due to the presence in it of PdS.