Catalyst supports activity determination

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

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. 

In Chapter 1 we emphasized that the properties of a heterogeneous catalyst surface are determined by its composition and structure on the atomic scale. Hence, from a fundamental point of view, the ultimate goal of catalyst characterization should be to examine the surface atom by atom under the reaction conditions under which the catalyst operates, i.e. in situ. However, a catalyst often consists of small particles of metal, oxide, or sulfide on a support material. Chemical promoters may have been added to the catalyst to optimize its activity and/or selectivity, and structural promoters may have been incorporated to improve the mechanical properties and stabilize the particles against sintering. As a result, a heterogeneous catalyst can be quite complex. Moreover, the state of the catalytic surface generally depends on the conditions under which it is used. 

The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

The surface of PSs is determined as an interface between the condensed phase and the space of the pores. For catalysts with supported active components textural characteristics of individual phases are important, including their accessible, surface areas and the interfacial surface areas [5,6],... 

Theoretical studies on the Beckmann rearrangement mechanism over zeolite catalyst supported by experimental data have increased. The catalytic activity of the zeohte is determined by Brpnsted and Lewis acid sites created by protonation or activation by metallic cations. The reactivity of the acid sites is strongly influenced by the geometry and flexibility of the zeolite framework ". ... 

The aluminophosphate molecular sieves have an interesting property for potential use as catalyst supports, due to their excellent thermal stabilities and unique structures. AIPO4-5 is known to retain its structure after calcination at 1000°C and have uni-directional channels with pore size of 8 A bounded by 12-membered rings [2]. To utilize molecular sieves as catalyst support, chemical interactions between the molecular sieve and active component, chemical stabilities, and surface structures must be determined. However, iittle attempt has been made to clarify the surface structures or properties of catalytically active components supported on the aluminophosphate molecular sieves. 

Monolayer coverage of vanadium oxide on tin oxide support was determined by a simple method of low temperature oxygen chemisorption and was supported by solid-state NMR and ESR techniques. These results clearly indicate the completion of a monolayer formation at about 3.2 wt.% V2O5 on tin oxide support (30 m g" surface area). The oxygen uptake capacity of the catalysts directly correlates with their catalytic activity for the partial oxidation of methanol confirming that the sites responsible for oxygen chemisorption and oxidation activity are one and the same. The monolayer catalysts are the best partial oxidation catalysts. 

FT-IR has been used to determine residual catalyst support in commercial polyethylene at the level of 100 parts per million 841. The method is based on the use of the 1118 or 470 cm-1 bands to determine the quantity of silica support dispersed in the polymer. The band at 2020 cm-1 was used as an internal standard for the amount of polyethylene. Neutron activation analysis was used to calibrate the weight percent of silica present in each polymer sample. 

We seek to determine how the activity (y and durability (y2) of a platinum catalyst supported by a nonporous metal carrier depend on the catalyst composition at 350 °C. The total mass of components was maintained constant from experiment to experiment. Taking it to be unity, we can write ... 

Thermal Baseline Study. PDU Run 2LCF-21 (Thermal Baseline) processed a 70/30 volume percent SRC-I/500°F IBP KC-Oil feed blend over an inert 1/32 inch Shell catalyst support. The inert support was the extrudate base for the modified Shell 324 catalyst and had been calcined at 1100-1150°C. The purpose of this run was to determine the extent of conversion and denitrogenation in the absence of an active catalyst ingredient - nickel and molybdenum (Ni/Mo). 

Tris-allyl-neodymium Nd(//3-C3I Ishdioxane which performs as a single site catalyst in solution polymerization was heterogenized on various silica supports which differed in specific surface area and pore volume. The catalyst was activated by MAO. In the solution polymerization the best of the supported catalysts was 100 times more active (determined by the rate constant) than the respective unsupported catalyst [408]. 

In addition to the studies in which supported catalysts are exclusively used for gas-phase polymerizations one study is available in which the supported catalyst is optimized in a solution process prior to its application in the gas phase. Tris-allyl-neodymium [Nd(/ 3- C3H5)-dioxane] which is a known catalyst in solution BD polymerization is heterogenized on various silica supports differing in specific surface area and pore volume. The catalyst is activated by MAO. In solution polymerization the best of the supported catalysts is 100 times more active (determined by the rate constant) than the respective unsupported catalyst [408]. In addition to the polymerization in solution, the supported allyl Nd catalyst is applied for the gas-phase polymerization of BD [578,579] the performance of which is characterized by macroscopic consumption of gaseous BD and in-situ-analysis of BD insertion [580]. 

Declustering seems to be also possible by the application of appropriate catalyst supports. For tris-allyl-neodymium Nd(r/3- C3H5P dioxane the rate constants for monomer consumption are determined for supported as well as for unsupported catalysts. Under comparable experimental conditions the respective rate constants differ by a factor of 100. This observation can be explained by differences in Nd efficiency or by differences in the concentration of active Nd sites [408]. 

Natta postulated that for the stereospecific polymerization of propylene with Ziegler-Natta catalysts, chiral active sites are necessary he was not able to verify this hypothesis. However, the metallocene catalysts now provide evidence that chiral centers are the key to isotacticity. On the basis of the Cossee-Arlman mechanism, Pino et al. (164,165) proposed a model to explain the origin of stereoselectivity The metallocene forces the polymer chain into a particular arrangement, which in turn determines the stereochemistry of the approaching monomer. This model is supported by experimental observations of metallocene-catalyzed oligomerization. 

The hydrogenation of a-methylstyrene was investigated to demonstrate the performance of a packed-bed microreactor with a palladium catalyst supported on activated carbon [324]. The microreactor was operated at 50 °C, and conversions from 20 to 100% were measured. It was determined that the reaction is first order for hydrogen and zero order for a-methylstyrene. Initial reaction rates were close to 0.01 mol/min per reaction channel and were achieved without additional activation of the catalyst. This is in agreement with the literature data on intrinsic kinetics. 

Catalytic tests in sc CO2 were run continuously in an oil heated flow reactor (200°C, 20 MPa) with supported precious metal fixed bed catalysts on activated carbon and polysiloxane (DELOXAN ). We also investigated immobilized metal complex fixed bed catalysts supported on DELOXAN . DELOXAN is used because of its unique chemical and physical properties (e. g. high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions). The effects of reaction conditions (temperature, pressure, H2 flow, CO2 flow, LHSV) and catalyst design on reaction rates and selectivites were determined. Comparative studies were performed either continuously with precious metal fixed bed catalysts in a trickle bed reactor, or discontinuously in stirred tank reactors with powdered nickel on kieselguhr or precious metal on activated carbon catalysts. Reaction products were analyzed off-line with capillary gas chromatography. 

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