Catalyst platinum/palladium partial oxidation

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. 

Poisoning of metal catalysts may provide a tool for improving selec> tivity by affecting the concentrations of ensembles required by different reaction paths. This is illustrated by steam reforming on sulfur passivated nickel catalysts and the results are compared with observations for sulfided platinum-rhenium catalysts for catalytic reforming and for a chlorine poisoned palladium catalyst for partial oxidation of methane. 

Palladium was a common element in oxidation catalysts where it was used together with platinum, in a mass ratio of about 5 2 Pt Pd at a total precious metal loading of about 1.5 gU catalyst volume. Some three-way catalysts used palladium together with platinum and rhodium, in which the palladium was a partial replacement of platinum. The loadings used were 0.9-3.IgPt, 0.0-3. Ig Pd and 0.15-... 

Metal-based catalysts also were used for methane oxidation. Especially over metals such as platinum and palladium, trace amounts of methanol, formaldehyde, and formic acid can be found. Organic halides increased the yield of partial oxidation products and inhibited the complete combustion of methane [173]. Inhibition effects of dichloromethane was observed. Mann and Dosi [174] used a Pd/Al203 catalyst and found that the addition of halogen compounds reduced the conversion of methane in the following order ... 

The presence of thallium(0) led to an increase in activity and selectivity of metallic palladium catalysts supported on silica in aldose oxidation reactions. However, silica-supported thallium(0) had no activity by itself (entry 3). ° Similarly, the bimetallic catalyst platinum-thallium/ZSM-5, prepared by impregnation of thallium sulfate and chloroplatinic acid on Zeolite Socony Mobil-5 (ZSM-5), showed greater selectivity in propane aromatisation and almost the same catalytic activity as monometallic thallium/ZSM-5 (entry 4). Similar comparison of vanadium-caesium-copper and vanadium-caesium-copper-thallium catalysts supported on TiOa.SiC demonstrated that addition of thallium improved the catalytic activity in partial oxidation of p-tert-butyltoluene to p-tert-butyl-benzaldehyde (entry The application of solid-supported thallium-based catalysts in different processes includes (a) iron-thallium catalysts in carbon monoxide hydrogenations to form hydrocarbons and alcohols, and catalytic reforming of... 

The catalytic oxidation takes place with precious metal catalysts (platinum and/or palladium on aluminium oxide carriers) at temperatures between 200 and 600 °C. When the reactor exit temperature reaches only about 450 °C the remaining methane has to be removed in the CO2 stripper. If the required oxygen is added to the CO2 in the form of air, then the nitrogen mixed with the CO2 has also to be separated again in the COj stripper. The CO2 partial pressure is lower and therefore the recovery rate is lower (see Fig. 6.6). 

The metal catalysts active for steam reforming of methane are the group VIII metals, usually nickel. Although other group VIII metals are active, they have drawbacks for example, iron rapidly oxidizes, cobalt cannot withstand the partial pressures of steam, and the precious metals (rhodium, ruthenium, platinum, and palladium) are too expensive for commercial operation. Rhodium and ruthenium are ten times more active than nickel, platinum, and palladium. However, the selectivity of platinum and palladium are better than rhodium [1]. The supports for most industrial catalysts are based on ceramic oxides or oxides stabilized by hydraulic cement. The commonly-used ceramic supports include a-alumina, magnesia, calcium-aluminate, or magnesium-alu-minate [4,8]. Supports used for low temperature reforming (< 770 K) are... 

In general the reduction of a pyridine side-chain acid or ester using platinum oxide, Raney Nickel, rhodium-on-carbon, rhodium-on-alumina, or ruthenium oxide as the catalyst gives the piperidine acid or ester. Partial reduction of the pyridine ring to a tetrahydropyridine usually occurred when palladium-on-carbon was employed as the catalyst, although two exceptions were reported. Either a mixture of the piperidine and the tetrahydropyridine ester or the tetrahydropyridine ester alone was formed when sodium borohydride was used at room temperature in the reduction of pyridine side-chain ester salts. When the free bases were employed, reduction of the ester group occurred instead of nuclear reduction. The use of lithium aluminum hydride gave the same results (see Table XI-18). Many acetamides... 

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