Carbon catalyst dispersion, preparation

Palladium supported on alumina or active carbon catalysts were prepared using ultrasound during the preparation steps. A large increase in the metal dispersion and in the catalytic activity of the samples, tested during the reduction of acetophenone with flowing hydrogen, was found. 

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

The anchoring and the reduction methods of precious metal precursors influence the particle size, the dispersion and the chemical composition of the catalyst. The results of SEM and H2 chemisorption measurements are summarised in Table 3. The XPS measurements indicate that the catalysts have only metallic Pd phase on their surface. The reduction of catalyst precursor with sodium formate resulted in a catalyst with lower dispersion than the one prepared by hydrogen reduction. The mesoporous carbon supported catalysts were prepared without anchoring agent, this explains why they have much lower dispersion than the commercial catalyst which was prepared in the presence of a spacing and anchoring agent (15). 

The catalyst was prepared by impregnation of the powdered activated carbon support, Norit SX Ultra, (surface area 1200 m g ) with sufficient palladium nitrate to produce a metal loading of 3 %. The resulting suspension was dried and calcined at 423 K for 3 hours. The dispersion of the catalyst was... 

The support porous structure and the rate of solvent removal from the pores as well as the nature of solvent and metal compound dissolved can considerably influence both the distribution of the active component through the support grain and the catalyst dispersion [163,170-173]. As a rule, the resulting particles size of the active component will be smaller, the more liquid-phase ruptures caused by evaporation of the solvent from the support pores are attained before the solution saturation. Therefore, supports with an optimal porous structure are needed to prepare impregnated Me/C catalysts with the finest metal particles. As a result, carbon supports appropriate for synthesis of such catalysts are very limited in number. Besides, these catalysts will strongly suffer from the blocking effect (see Section 12.1.2) because some of the metal particles are localized in fine pores. 

The Pd/ZrOj catalyst was prepared by impregnation. PdClj (PGP Industries Ireland) was dissolved in sufficient dilute hydrochloric acid to fully wet the zirconia (Degussa, S. A. 50m g ). The resulting mixture was evaporated to dryness at 353 K. The weight loading obtained was 0.99 % w/w Pd/zirconia. The dispersion of the catalyst was determined by carbon monoxide chemisorption at 96 %, assuming a ratio of 1 2 for CO Pd. 

These catalysts were prepared according to the following proc ure. The adequate amount of palladium acetate was dispersed in the presence of the activated carbon (2.7 g) in about 100 ml n-heptane under ultrasonic stirring for 30 min. After slow evaporation of the solvent at room temperature, the appropriate amount of bismuth oxoacetate was deposited on the obtained monometallic catalyst according to the same procedure. The bimetallic catalyst was then activated upon thermal heating under nitrogen at 773 K during 18h. 

Similar excellent results are obtained by combining a 5 % Ru-on-carbon catalyst with an acidic zeolite catalyst (H-USY, H-mordenite or H-ZSM-5). Ru-H-USY preparation zeolite NaY is exchanged with aq. NH4C1 (100 molar excess) at room temperature, washed, calcined (12 h, 450 °C) and the procedure repeated twice to obtain an essentially Na-free H-USY. Ru is incorporated by ion exchange with 0.05 M aq. Ru(NI fi Ch. The material is reduced by healing in H2 at 2 °C / min to 400 °C to obtain 3 % Ru in H-USY with a Ru dispersion of 0.73 (by CO adsorption). 

Low-platinum catalysts are prepared in combination with amorphous, hydrous transition-metal oxides. The catalysts are dispersed in carbon inks, and their electrocatalytic activity is screened in half-cell measurements. 

Catalysts were prepared by impregnation of Pt inside the pore structure of carbon fibers. Care was taken to eliminate the active metal from the external surface of the support. A very high dispersion of Pt was measured. Four reactions were carried out in a fixed-bed reactor competitive hydrogenation of cyclohexene and 1-hexene, cyclization of 1-hexene, n-heptane conversion and dehydrogenation of cyclohexanol. Three types of carbon fibers with a different pore size and Pt-adsorption capacity along with a Pt on activated carbon commercial catalyst were tested. The data indicate a significant effect of the pore size dimension on the selectivity in each system. The ability to tailor the pore structure to achieve results drastically different from those obtained with established supports is demonstrated with heptane conversion. Pt on open pore carbon fibers show higher activity with the same selectivity as compared with Pt on activated carbon catalysts. 

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