Mixed-oxide supports

Recent Advances on NO Reduction Related to Mixed Oxides, Supported Metals and Ion-Exchange Mesoporous... 

Silica-alumina is the most popular mixed oxide support, combining characteristic features of silica and alumina, including (i) high surface area, (ii) persistent OH population at high temperature and (iii) strong Lewis acidic sites. The predominant surface hydroxyl groups on silica-alumina are [=Si-OH], while [Als-OH] surface species have not been observed [79, 89, 90]. Note that the silica-alumina bulk is mainly composed of [=Si-0-Si=] along with [=Si-0-Als] moieties (Lewis... 

Si02 is the best catalyst support for this reaction. As AI2O3 is incorporated into the Si02 the catalyst activity and selectivity decreases significantly. In these mixed oxide support materials Bronsted acid sites favour acylation, whilst the presence of Lewis acid sites results in hydrolysis of the anhydride. 

The samples prepared have a good surface area after calcination at 500°C, as can be seen in table 1. Alumina-titania mixed oxide supported samples have surface areas larger than those of the alumina and titania single oxides. As expected x-ray diffraction results show that the mixed oxide catalysts are amorphous, but alumina shows a y phase structure, and Ti02 is a well crystallized anatase phase. No nickel metal or nickel oxide was detected in any of the samples, including Ti02 sample, suggesting the metal was well dispersed, and present as small crystallites (< 50A). 

It is interesting to note also that the mixed oxide supported catalysts increase their activity with reduction temperature, although the impregnated sample performs better. In all cases ethylene selectivity was lower for alumina-supported sample and higher for titania-supported catalyst, and after an initial period the selectivity remained constant. 

Acetonitrile can be produced by catalytic ammoxidation of ethane and propane over Nb-Sb mixed oxides supported on alumina, with selechvities to acetonitrile of about 50-55% at alkane conversions of around 30% [133]. In both cases, CO forms in approximately a 1 1 molar ratio with acetonitrile, owing to a parallel reaction from a common intermediate. When feeding n-butane, the selectivity to acetonitrile halves. Bondareva and coworkers [134] also studied ethane ammoxidation over similar types of catalyst (V/Mo/Nb/O). 

Chemical and Nanostructural Aspects of the Preparation and Characterisation of Ceria and Ceria-Based Mixed Oxide Supported Metai Cataiysts ... 

CHEMICAL AND NANOSTRUCTURAL ASPECTS OF THE PREPARATION AND CHARACTERISATION OF CERIA AND CERIA BASED MIXED OXIDE-SUPPORTED... 

Additional measurements on a full series of ceria and cerium-zirconium mixed oxides supported noble metals showed that Ru was at least 10000 times more active than Pd and about 20 times more active than Rh for the activation of oxygen [70]. Up to now, most results were obtained with Rh catalysts but Ru could be a good candidate for surface diffusion measurements. 

PREPARATION OF ZIRCONIA-SILICA MIXED OXIDE SUPPORTS... 

The demand for mixed oxide chromatographic-quality stationary phase materials is small and only a few methods that detail their preparation are available in the hterature. There are, however, numerous examples of the preparation of zircon powders and Ref. [4] is an example of such a process. In general, these types of powders are unsuitable for chromatographic stationary phases because their particle sizes are in the submicron range with very broad distributions. The synthesis of mixed oxide supports for chromatographic apphcations can essentially be divided into two types coprecipitation methods and coating methods. 

Future work in stationary phase design will probably continue to include studies on mixed oxide composites although these will continue to constitute only a small fraction of the stationary phase materials made for general purpose use. Many of the mixed oxide supports will be custom-made for specific applications, and at least in the short term, these types of stationary phases will be made by individual research groups. 

The future of Raman spectroscopy in the research and the development of catalysts appears to be extremely promising. The recent revolution in Raman instrumentation has dramatically increased the ability to detect weak Raman signals and to collect the data in very short times. Thus, it is now possible to perform real-time Raman analysis and to study many catal) c systems that give rise to unusually weak Raman signals. The enormous strides in Raman instrumentation now allow for the characterization of a wide range of catalytic materials bulk mixed oxides, supported metal oxides, zeolites, supported metal systems, metal foils, as well as single crystal surfaces. Few Raman studies have been reported for sulfides, nitrides, or carbides, but these catalytic materials also give rise... 

Dhar, G.M., Srinivas, B.N., Rana, M.S., Kumar, M., and Maity, S.K. Mixed oxide supported hydrodesulfurization catalysts—A review. Catalysis Today, 2003, 86, 45. 

In the search for novel, more stable and efficient supports for gold catalysts for the WGS, mixed oxide supports (Fe203-Zn0 and Fe203-Zr02), as well as supports of a different crystalline state—amorphous zirconia and titania—have been used also by Andreeva and co-workers (Fig. 6.6) [228]. Gold deposited on well-crystallised metal oxides was found to have higher... 

Figure 10.10. CO (solid curves) and CO2 (dashed curves) signals measured in alternating pulses of 0.5%02 and 1% CO over a 2%Pd on 70wt% ceria-30wt% zirconia mixed oxide support model catalyst after redox aging at 1050°C (a) without SO2 in the feed, (b) with 10 ppm SO2 in the He carrier gas. (H. Jen)...

Low-temperature OSC via Ceria-praseodymia Mixed Oxide Support Phases... 

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