Catalysts shift

These models indicate that propylene gas phase polymerization with a highly active TiCil3 catalyst shifts from kinetic control at short reaction times to diffusion control at longer times as the catalyst yield exceeds about 4000 g.PP/g.TiCil3. Measures to reduce this limitation would significantly benefit the process. 

According to B3LYP/6-31G computations of the intermediates and TSs, there are no large barriers to the reaction and it is strongly exothermic.156 Measured Ea values are around 10kcal/mol.157 The complexation of borane to the catalyst shifts electron density from nitrogen to boron and enhances the nucleophilicity of the hydride. The... 

I. Catalysts shift an equilibrium to favor product formation. 

Shell-side effluent from the reforming exchanger is cooled in a waste-heat boiler, where HP steam is generated, and then flows to the CO shift converters containing two catalyst types one (4) is a high-temperature catalyst and the other (5) is a low-temperature catalyst. Shift reactor effluent is cooled, condensed water separated (6) and then routed to the gas purification section. C02 is removed from synthesis gas using a wet-C02 scrubbing system such as hot potassium carbonate or MDEA (methyl diethanolamine) (7). 

Some interesting conclusions can be drawn from the TPR experiments (Figure 1). First, the reduction feature of RU/AI2O3 catalyst differs from that observed for Ru/AC. Ruthenium precursors supported on carbon are reduced at lower temperatures. This fact is indicative of different metal-support interactions. Furthermore, in all the AC supported catalysts a second H2 consumption peak appears at temperatures close to 673 K. This peak is accompanied by the production of CH4, which can be originated by the partial gasification of the carbon species of the support near the metal particle [10]. Also, this peak near 673 K could indicate the presence of some Ru" species stabilized by interaction with the carbonaceous support, which would become reduced at this temperature. Moreover, the addition of MgO to the Ru/C catalyst shifts the reduction of ruthenium to higher temperatures. Thus, we can deduce that in the Ru-Mg/AC catalysts the ruthenium particles are in close interaction with the MgO. 

Recently, Comas et al.219 performed the thermodynamic analysis of the SRE reaction in the presence of CaO as a C02 sorbent. The equilibrium calculations indicate that the presence of CaO in the ethanol steam reforming reactor enhances the H2 yield while reducing the CO concentrations in the outlet of the reformer. Furthermore, the temperature range at which maximum H2 yield could be obtained also shifts from above 700 °C for the conventional steam reforming reaction without CaO to below 700 °C, typically around 500 °C in the presence of CaO. It appears that the presence of CaO along with ethanol reforming catalyst shift the WGS equilibrium in the forward direction and converts more CO into C02 that will be simultaneously removed by CaO by adsorption. 

Zeolites as co-catalysts shift the product distribution because their acid sites can carry out secondary reactions such as alkylation, cracking, oligomerization, and isomerization. These reactions can be important in shifting selectivities toward high-octane gasoline or olefins. 

Adding L has effects which are the opposite of diluting catalyst shifting more of the reaction to lower planes reduces the turnover rate, but reduces hydrogenation and isomerization rates even more, while increasing the i CHO/i CHO ratio. The negative effect of [CO] on product isomer ratio can be understood in terms of competition between CO and L for coordination. 

The structural promoter functions to provide a stable, high-area catalyst, while the chemical promoter alters the selectivity of the process. The effectiveness of the alkali metal oxide promoter increases with increasing basicity. Increasing the basicity of the catalyst shifts the selectivity of the reaction toward the heavier or longer-chain hydrocarbon products (Dry and Ferreira, 1967). By the proper choice of catalyst basicity and ratio, the product selectivity in the Fischer-Tropsch process can be adjnsted to yield from 5% to 75% methane. Likewise, the proportion of hydrocarbons in the gasoline range ronghly can be adjnsted to produce 0%-40% of the total hydrocarbon yield. 

Compared with the Ag/C catalysts, the half-wave potentials for the ORR cat the FePc Ag/C, CoPc Ag/C, MnPc Ag/C, and NiPc Ag/C catalysts shifted positively about 178, 64, 32, and 24 mV, respectively. The kinetic currents obtained on the FePc Ag/C, CoPc Ag/C, MnPc Ag/C, and NiPc Ag/C catalysts were about 67.85, 3.09,1.53, and 1.37 times higher than what was observed on the Ag/C catalyst at 0.68 V (vs. RHE), respectively. The MPc Ag/C catalysts are more active toward the ORR than the Ag/C catalyst with a trend of FePc Ag/C > CoPc Ag/C > MnPc Ag/C > NiPc Ag/C. Based on the observed limiting disk currents and ring currents on the RDE or RRDE, the ORRs on various MPc Ag/C catalysts were found to occur via a 4e ORR pathway, which suggests that the active sites for the O2 reduction on the MPc Ag/C catalysts are mainly on the Ag/C catalysts. The improved ORR... 

In both cases calcination of the catalysts shifts the temperature of soot combustion to higher temperature region 460 and 516°C for calcined biomorphic and coprecipitated catalysts correspondingly. It is worth mentiorung that even after calcination, soot combustion in presence of biomorphic system occurs at lower temperature than in presence of iiutial coprecipitated catalyst. 

Stems and leaves of the Chilean Euphorbia copiapina were analyzed by means of TG, DSC and combustion calorimetry to evaluate their quality as a source of botanochemical compounds and fuels, using various zeolitic catalysts [36]. The applied catalysts shifted the pyrolysis to mixtures with interest as fuels and indu-stnal chemicals. 

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