Activity at high temperatures

Activated alumina Hydrated aluminum oxide, a granular desiccant activated at high temperature that absorbs moisture and gases. 

The kinetic activities of noble metals and of base metal oxides are complementary, so that a mixture of the two would perform better than each class of material alone. We have already observed in Fig. 16 that noble metals have superior activity at high temperatures but base metal oxides have superior activity at low temperatures. Since the CO oxidation kinetics is negative first order with respect to CO over platinum but first order with respect to CO over copper chromite, the rates must be faster over platinum at low CO concentration but the reverse is true at high CO concentrations, as shown in Fig. 19. 

It is well known also that higher alkanes suffer radical gas phase oxidation above 723 K. Therefore, their use requires catalysts active and selective for deNOx at lower temperatures. The mechanism of NOx elimination is still debated a redox mechanism involving Cu ions is probable, and isolated Cu cations exchanged into MFI [4,5] or mordenite [6] have been found to be more active than CuO clusters. It must be emphasized, however, that acid zeolites exhibit good activity at high temperature, and acid mechanisms have been proposed [7-10]. In presence of Cu this acid mechanism disappears probably due to the decrease of the acidity of mordenite upon Cu exchange [6]. According to... 

At this point, we can schematically represent the structure of Cr(II) sites as (SiO)2Cr L , where L represents a weak ligand (oxygen of a SiOSi bridge) and n is a not fully known figure which increases upon activation at high temperature. The adsorption of CO at room temperature on grafted Cr(II) sites... 

C. Hsu, H. Nguyen, D. Yeung, D. Brookes, G. Koe, T. Bewley, and R. Pearlman, Surface denaturation of solid-void interface—a possible pathway by which opalescent particulates form during the storage of lyophilized tissue-type plasminogen activator at high temperatures, Pharm. Res., 12, 69 (1995). 

The points discussed in this appendix are of direct relevance to a description of the chemical reactions that involve surmounting the potential barrier. The barrier is surmounted due to thermal activation at high temperatures and due to tunneling at low temperatures, the latter fact accounting for an occurrence of low-temperature chemical reactions.216,217... 

Bacteria represent a promising source for the production of industrial enzymes. Bacterial cellulases are an especialfy interesting case in point. Many thermophilic bacterial species produce cellulases that are stable and active at high temperature, resistant to proteolytic attack, and stable to mechanical and chemical denaturation. However, cellulase productivities in bacteria are notoriously low compared to other microbial sources. In this paper bacterial enzyme production systems will be discussed with a focus on comparisons of the productivities of known bacterial cellulase producers. In an attempt to draw conclusions concerning the regulation of cellulase synthesis in bacterial systems, a tentative model for regulation in Acidothennus cellulofyticus has been developed. 

Spinel oxides are important industrial catalysts, possessing good thermal and chemical stability and an ability to maintain catalytic activity at high temperatures. The study reported here is concerned with the properties ofZn(II)-Cr(III) spinel oxides prepared from a carbonate containing LDH precursor. For this study the spinel oxide was separated, by treatment with dilute mineral acid, from the oxide mixture (ZnO and ZnC O, ) obtained by the thermal decomposition of LDH. For comparison, Zn(II)-Cr(lII) spinel oxides were also prepared by more standard synthesis methods. Structural and textural properties were evaluated, using PXRD, TG/MS, FT-IR and N2 adsorption. 

MgO powders activated at high temperatures have been known for many years to promote the heterolytic cleavage of hydrogen and methane molecules [1, 2], The interest in this kind of reactions is motivated by the great technological relevance of the realization of heterogeneous catalysts capable of promoting in an efficient way the partial oxidation of methane [3], While it is well established that the perfect (001) face, by far the most stable surface of crystalline MgO, is practically inert, it is not yet clear which types of defect at that face are responsible for its activity. 

A number of ortho hindered alkyl-substituted phenyl phosphites and phosphonites were found to be effective process stabilizers for polypropylene and high density polyethylene combining more effective stabilization activity at high temperatures with good storage stability at relatively elevated humidity and ambient temperature, as well as resistance to discoloration. 

A significant improvement in the asymmetric isomerization came on the discovery of Rh(,S-BINAP)2]+BF4. This catalyst shows remarkable catalytic activity at high temperature (>80°C) without deterioration of stereoselectivity (>96% ee). The TON is improved to 400,000 through catalyst recycle (2% loss of catalyst per reuse). Additional improvements in the catalyst have been achieved by modification of the BINAP to p-TolBINAP (3b).42... 

These observations imply that no oxygen remains unreactcd with carbon above 350 K, which is in line with the catalytic function of carbon exhibiting no oxidation activity at high temperatures. This precludes, however, the possibility that any of the species detected so far can act as efficient precursors for carbon oxidation which begins with the emission of CO at significantly higher temperatures. 

Yellow mercuric oxide reacts only slightly with CO near room temperature, but the activity can be increased markedly by the addition of chromic acid anhydride (58). Thorium oxide is an active catalyst at temperatures above 400°C., and its activity can be increased by the addition of 0.96% Ce203 (60). Vanadium pentoxideis also active at high temperatures (61). 

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