Catalysts containing cerium

After hydrothermal treatment with steam, the loss of surface area of the reference zeolite was 28%, while the loss of surface area of the catalysts containing cerium was not more than 21%. The PP25 sample presented a small loss of surface area, and was therefore more resistant. The EX and IMP catalysts presented similar losses of surface area, around 20-21%. 

Two of the materials were furnished by catalyst companies and are referred to as magnesia-based or magnesia and lanthanum-based or lanthanum. These latter materials are both known to contain cerium and alumina as well. 

In general, the catalysts contain varying quantities of the oxides of aluminum, potassium, calcium, magnesium, and silicon as promoters. Patents recommend adding sodium [243], beryllium [244], vanadium [245], uranium [246], or platinum [247]. Reference [248] describes cesium-containing catalysts. Catalysts patented by Lummus [249] and Ammonia Casale [250] contain cerium as additional promoter. ICI [251] has developed a cobalt-containing catalyst, as has Grande Paroisse [252]. 

It was noted in the introduction that the washcoat of the automobile catalysts contains several other oxides, mainly cerium and lanthanum oxide. 

The control of sulfur oxide emissions is becoming more important. Several catalyst additives containing cerium and/or lanthanides can act as the SOX control agent (16]. 

A more detailed investigation, including the effect of varying the amount of cation exchange, was undertaken for catalysts containing zinc and cerium cations as they were both active at low temperatures but exhibited different product selectivities. A similar study of the nickel-exchanged zeolite will be reported elsewhere (8). 

Catalysts for the chemical industry have to be characterized with respect to their trace impurities and major components. Not only is their composition when they are used initially in chemical reactors important, but also their alteration in the course of time. As carbide forming elements such as V and Ti are often used, atomic absorption spectrometry could be problematic. This also applies to catalysts for exhaust gas detoxification in cars. Noble metals such as Pt, Pd and Rh are fixed on alumina supports often also containing cerium compounds. Both for the determination of the stoichiometry but also for the monitoring of the noble metal contents in used catalysts, AAS suffers from problems because of the need for sample dissolution as well as for the requirement to determine refractory oxide forming elements. 

Platinum is an effective oxidation catalyst for carbon monoxide and the complete oxidation of hydrocarbons. Palladium also promotes the oxidation of carbon monoxide and hydrocarbons but is more sensitive to poisoning than platinum in the exhaust environment. Both platinum and palladium promote the reduction of nitric oxide but are less effective than rhodium. In addition to the noble metals, three-way catalysts contain the base metal cerium and possibly other additives such as lanthanum, nickel or iron. These base metal additives are believed to improve catalyst performance by extending conversion during the rapid air-fuel ratio perturbations and help to stabilize the alumina support against thermal degradation. 

The R sources used for preparing FCC catalysts are monazite and bastnaesite sands which predominantly contain cerium, lanthanum and neodymium their detailed composition is given in table 5 (Magee and Blazek 1976). 

Pseudoboehmite hydroxide obtained via procedure developed in [11], was used to extrude alumina in rings. Before the moulding, hydroxide was modified via a direct introduction of nitric acid salts of lanthanum or cerium. The content of the modifying ion (2 wt.% Me 02n) was selected by data of [6,7]. The modified supports were consequently dried and thermally treated at room temperature (10 h), 383 K (4 h), 773 K (8 h) and 1173 K (8 h).The support was impregnated with solutions of the required content of Cu(N03)2, CrOs or [CuCr207-t-Cu(N03)] by the incipient wetness impregnation method, then consequently dried at room temperature and under IR lamps for 4 hours. Catalysts were thermally treated in air at 778 K ( 4 h ) and at 973 and 1273 K (2 h). The catalysts contained 2, 7 and 15 wt.% of the active component for [Cu-I-Cr] system, the Cu Cr = 2 1 ratio was maintained. 

VeUe, O.J., Andersen, A., and Jens, K.J. The oxidative dehydrogenation of ethane by perovskite type catalysts containing oxides of strontium, cerium and ytterbium. Catal Today 1990, 6,567. 

Catalyst for ammonia synthesis containing cerium as an additional promoter. (Ammonia Casale SA). IT-A47920A (1979). 

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