Oxide catalysts comparisons

Liotta, L., Ousmane, M., Di Carlo, G., etal. (2009). Catalytic Removal of Toluene over C03O4-Ce02 Mixed Oxide Catalysts Comparison with Pt/Al203, Catal. Lett., 127, pp. 270-276. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

In this paper we attempt a preliminary investigation on the feasibility of catalytic combustion of CO/ H2 mixtures over mixed oxide catalysts and a comparison in this respect of perovskite and hexaaluminate type catalysts The catalysts have been characterized and tested in the combustion of CO, H2 and CH4 (as reference fuel). The catalytic tests have been carried out on powder materials and the results have been scaled up by means of a mathematical model of the catalyst section of the Hybrid Combustor. 

Figure 10.5. Comparisons of the conversion obtained on Ag/alumina in combination with Pt oxidation catalyst in the presence of hydrogen. 500 ppm NO, 375 ppm C8H18, 1 vol.% H2, 6 vol.% 02, 10vol.% C02, 350ppm CO, 12vol.% H20 in He. GHSV = 60000h 1 (reproduced with permission from Ref. [72]).

A wide range of nonacidic metal oxides have been examined as catalysts for aromatization and skeletal isomerization. From a mechanistic point of view, chromium oxide catalysts have been, by far, the most thoroughly studied. Reactions over chromium oxide have been carried out either over the pure oxide, or over a catalyst consisting of chromium oxide supported on a carrier, usually alumina. Depending on its history, the alumina can have an acidic function, so that the catalyst as a whole then has a duel function character. However, in this section, we propose only briefly to outline, for comparison with the metal catalyzed reactions described in previous sections, those reactions where the acidic catalyst function is negligible. 

Comparison of promoted alkaline-earth oxide catalysts prepared through evaporation and sol-gel methods by their catalytic performance in propane oxidative dehydrogenation... 

Comparison of promoted alkaline-earth oxide catalysts... 

NMR, EPR, EXAFS, infrared, resonance Raman, and ultraviolet-visible spectroscopy should follow. Kinetic and thermodynamic information about the model complexes in comparison to that known for natural systems should be gathered. These concepts were updated in 1999 by Karlin, writing in reference 49. Model studies should provide reasonable bases for hypotheses about a biological structure and its reaction intermediates. Researchers should determine the model s competence in carrying out reactions that mimic metalloprotein chemistry. Using these methods and criteria, researchers may hope to exploit Cu-oxygen systems as practical dioxygen carriers or oxidation catalysts for laboratory and industrial purposes. 

Table 115 CO conversion comparison of Au/thoria with reference Au/oxide catalysts using a feed containing 4.42%CO in Ar, a SV = 4000 h and a partial pressure of HzO of 31.1 kPa509... 

Priest, M. W., D. J. Williams, and H. A. Bridgman. (2000). Emissions from in-use lawn-mowers in Australia. Atmospheric Environment 34(4) 657-664. Sawyer, R. R, R. A. Harley, S. H. Cadle, J. M. Norbeck, R. Slott, and H. A. Bravo. (2000). Mobile sources critical review 1998 NARSTO assessment. Atmospheric Environment 34(12-14) 2161-2181. Christensen, A., R. Westerholm, and J. Almen. (2001). Measurement of regulated and unregulated exhaust emissions from a lawn mower with and without an oxidizing catalyst A comparison of two fuels. Environmental Science and Technology 35(11) 2166-2170. 

Anotlier example of dendritic POM complexes used as recoverable oxidation catalysts was reported by Plault et al. (SS). A series of ionic polyammonium dend-rimers containing between 1 and 6 POM units were prepared and used to catalyze the epoxidation of cyclooctene in a biphasic water/CDCls system. A comparison of the homogeneous mono-, bis-, tris-, and tetra(POM) catalysts indicated that there was no dendritic effect on the reaction kinetics within this series. However, a dendritic effect was found in the recovery of the catalysts. The dendritic catalysts were precipitated from the organic phase by addition of pentane. The recovery of the tri-and tetra-(POM) catalysts was easier (80—85% and 96%, respectively) than that of the mono(POM) catalyst. 

Aramendia et al. (22) investigated three separate organic test reactions such as, 1-phenyl ethanol, 2-propanol, and 2-methyl-3-butyn-2-ol (MBOH) on acid-base oxide catalysts. They reached the same conclusions about the acid-base characteristics of the samples with each of the three reactions. However, they concluded that notwithstanding the greater complexity in the reactivity of MBOH, the fact that the different products could be unequivocally related to a given type of active site makes MBOH a preferred test reactant. Unfortunately, an important drawback of the decomposition of this alcohol is that these reactions suffer from a strong deactivation caused by the formation of heavy products by aldolization of the ketone (22) and polymerization of acetylene (95). The occurrence of this reaction can certainly complicate the comparison of basic catalysts that have different intrinsic rates of the test reaction and the reaction causing catalyst decay. 

In some cases, the effect of reactant structure may outweigh the influence of catalyst nature. This is seen by comparison with the dehydration of aliphatic secondary alcohols and substituted 2-phenylethanols on four different oxide catalysts (Table 4). With aliphatic alcohols, the slope of the Taft correlation depended on the nature of the catalyst (A1203 + NaOH 1.2, Zr02 0.3, Ti02—0.8, Si02—2.8 [55]) whereas for 2-phenyl-ethanols, the slope of the corresponding Hammett correlation had practically the same value (from —2.1 to —2.4) for all catalysts of this series [95]. The resonance stabilisation of an intermediate with a positive charge on Ca clearly predominates over other influences. 

In a bulk polymerization study initiated with BF3-ethylene oxide catalyst at 0° C, Ofstead (34) obtained quite narrow molecular weight distributions over the range from five to forty percent conversion. The comparison of his data for a PTHF of DP 96 with the theoretical curve for a Poisson distribution is shown in Fig. 23. 

The valence of the starting organochromium compound has been varied from Cr(0) to Cr(IV), but seems to make little difference. All species are quite active, and all initiate polymerization rapidly in comparison to the oxide catalysts. There is no induction time, since the chromium is already reduced, and no gradual rise in rate. Polymerization usually starts immediately on contact with ethylene and either holds steady or slowly declines during a 1 hr run. 

HMF oxidation. In comparison with the oxidation of methanol, the picture changes significantly when oxidizing HMF. First of all, the type of oxygen tolerance changes for all Pd and Pt catalysts the catalyst is not poisoned by oxygen anymore, indicating a protection of the noble metal surface by HMF. Also in the case of Rh, however, the catalyst is not protected by HMF, so this catalyst shows the same stability as for the oxidation of methanol. In the cases of Ru and Ir the catalyst is deactivated, which means that these metals only have a small interaction with the substrate and/or are unable to oxidize HMF at these reaction conditions. 

This method was developed to replace the hazardous mercury catalyst required in the original mercuric oxide Kjeldahl method. It has been evaluated through an interlaboratory comparison of catalysts and has been adopted as the official replacement for the mercuric-oxide catalyzed Kjeldahl method. An inter-laboratory evaluation (Berner, 1990) indicated that this method (which uses the copper/titanium catalyst mixture) produces results more closely in agreement with the mercuric oxide catalyst method than methods using a copper sulfate catalyst. As a result of this study, mercuric... 

Tests on the activity of LP-produced Fe-based nanopowders for liquefaction of a sub-bituminous coal under high (688 K, 1 h of reaction) and low (658 K, 0.25 h of reaction) severity conditions have been reported.38 The catalysts tested were Fe7C3 (92 m2 g 1 (BET), particle size = 17 nm (XRD))and Fe XS (42 m2 g 1 (BET), particle size = 14 nm (XRD).38 For comparison, a commercial superfine iron oxide catalyst (SFIO, supplied by Mach I, Inc.) whose major phase has been identified in one study as y-Fe20339 (surface area = 195 m2 g 1 (BET), particle diameter = 3 nm (XRD)) and in other study as the ferrihydrite40 was also evaluated under similar conditions. The coal liquefaction experiments were carried out in 50 cm3 horizontal microautoclave reactors loaded with 3 g of sub bituminous Black Thunder coal and 5 g of tetralin used as hydrogen donor. Catalyst loadings of 0.7% and 1.4% of as-received coal... 

The investigation of the mechanism of olefin oxidation over oxide catalysts has paralleled catalyst development work, but with somewhat less success. Despite extensive efforts in this area which have been recently reviewed by several authors (9-13), there continues to be a good deal of uncertainty concerning the structure of the reactive intermediates, the nature of the active sites, and the relationship of catalyst structure with catalytic activity and selectivity. Some of this uncertainty is due to the fact that comparisons between various studies are frequently difficult to make because of the use of ill-defined catalysts or different catalytic systems, different reaction conditions, or different reactor designs. Thus, rather than reviewing the broader area of selective oxidation of hydrocarbons, this review will attempt to focus on a single aspect of selective hydrocarbon oxidation, the selective oxidation of propylene to acrolein, with the following questions in mind ... 

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