Spillover of Species Other Than Hydrogen

This explanation concerning the role of oxide catalysts in the gasification does not hold for temperatures below the Tammann temperature. In the kinetic studies of gasification of coal without an activator, it is frequently assumed that the reaction is not catalytic but is induced by direct gas-solid 

In the presence of H20 between 652 and 852°C, Pt is more efficient than other metals or oxides (149) in the gasification of Graphon, Sterling F-T, and Norit-A carbons. Since the reaction products are CO + H2 (and only CH4 if the gasification is carried out in H2), the spiltover species may be the products of dissociation of H20, probably H, O, and OH. 

In the catalytic oxidation of CO in the presence of pure Sn02, the reduction of the catalyst by CO (redox mechanism) is the rate-limiting step (order 1 for CO). If in the mixture Pd-Sn02 the spillover of CO from Pd to Sn02 is faster than the spillover of O atoms, this creates a higher concentration of CO chemisorbed on Sn02. The reoxidation of the catalyst becomes the rate-limiting step and the orders are now 0 for CO and 0.5 for 02, as noted above. 

Oxygen spillover was also advocated for reactions other than simple oxidations. Tascon et al. (151) studied the transformation of formamides to nitriles at 275°C on BiPMo catalysts prepared by a physcial mixture of powders of Mo03 and BiP04  

Finally, oxygen spillover has also been advocated in typically inorganic reactions. In an earlier work by Batley and Ekstrom (155), the phenomenon of spillover was not mentioned. Instead, the authors referred to a topochemi-cal heterogeneous catalysis for the reaction of UF4 with 02. This, however, can be understood through the spillover of oxygen. The reaction 

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