Alumina-based catalyst support combustion

A recent comparative investigation of the NO + CO reaction shows a significant rate enhancement in the formation of N2 on Ce0.98Pda02O2 8 prepared via a combustion synthesis method in comparison with conventional Pd-based catalysts supported on alumina... 

Cerium-based catalysts have been successfully used in several processes. For example, ceria (Ce02) is used as an additive [ 1,2] in modem automotive exhaust catalysts. Ceria acts as an excellent oxygen store [3-5] in the catalyst, which is thus rendered a very effective catalyst for combustion [6]. Moreover, addition of ceria to the automotive exhaust catalysts minimises the thermally induced sintering of the alumina support and stabilises the noble metal dispersion [7]. Ceria also enhances nitric oxide dissociation when added to various supported metal catalysts [8], which is another important function of the automotive exhaust catalyst. Recent investigations by Harrison et al have shown that ceria doped with certain lanthanides and promoted with copper and chromium have catalytic activities comparable to that of the noble metal catalysts [9]... 

Deactivation of Pd-based combustion catalysts supported on modified alumina... 

Silica-alumina has been used to support the CuO coupled with Ga203, and Sn02 dispersed phases to enhance the catalytic properties of CuO-based catalysts in reactions of environmental importance (hydrocarbon combustion, NO and N2O decomposition and reduction [88]). The acidic properties of such oxide systems were studied from a qualitative (nature of the acid sites) and quantitative (number, acid strength, and strength distribution of acid sites) points of view through the adsorption and desorption of two basic probes (ammonia and pyridine) by coupled volumetric-calorimetric technique and XPS and FT-IR spectroscopy. 

For a naphtha feedstock,. the catalyst is based on nickel deposited on calcium or magnesium silico-aluminate incorporating potasskun, or nkkel on an alumina support with uranium promoter. Nickel on calcium aluminate is generally used for post-combustion. 

A series of 7-aiumina- and silica-supported oxides as MnzOs, C03O4 and Sm-Mn, Sm-Co bimetallic combinations was prepared by incipient wetness impregnation of the supports with aqueous solutions containing the nitrates of the metals and citric acid. The results obtained with these catalysts in the acetone complete oxidation reaction have shown a predominant effect of the support and the transition metal nature. The silica-supported oxides exhibited a bulk-like behaviour with relatively little difference between the Mn and Co catalysts. In contrast, when supported on alumina the performance of the Mn catalysts was remarkably better than that of the Co-based ones. In this case, whereas the Sm-Mn catalysts maintained a rather good performance relative to that of Mn/Al203, the temperatures required for acetone combustion over the Sm-Co catalysts were significantly lower than the ones over C0/AI2O3. 

The light-off curves for acetone combustion over the catalysts based on the single Mn and Co oxides are presented in Fig. 1, and the corresponding values of the temperature T50 at which the acetone conversion reaches 50% are included in Table 1. It is clear from these results that the behaviour of the alumina-supported single metal oxides contrasts strongly with that of the silica-supported ones. The performance of Mn/Si-823 is very similar to the one of Co/Si-823 in accordance with the tendency of the respective unsupported Mn and Co oxides for this reaction... 

All present industrial catalyst systems are based on silver deposited on a slightly porous solid. The most widely used support is x-alumina, but silica-alumina and carborundum can also be employed. The specific surface area of the support, its porosity, and the pore size exert a considerable influence on the metal distribution at the surface, and consequently on catalytic activity. Several techniques are also available for fixing the silver, either by impregnation from a solution, or by deposition from a suspension. An initiator, usually consisting of alkaline earth or alkaline metals, can be added to the catalyst, but other metallic additions have also been recommended. Certain halogenated organic derivatives, such as dichloropropane, may increase selectivity in trace amounts (10 ppm in the feed), by reducing combustion side reactions. 

Palladium oxide combustion catalysts for high temperature uses and their preparation JP 09285730 Petroleum Energy Centre Catalyst system based on PdO supported on 5-alumina... 

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