Catalysis of H2, CO and alkane oxidation–combustion over Pt/Silica catalysts: evidence of coupling and promotion

Results are presented on the oxidative–combustion reactions of H₂, CO, methane and propane over polycrystalline-powdered silica-supported catalysts containing Pt (and possibly oxide promoters, e.g. MnO₂, etc.) and the coupling of different combustion processes and also heterogeneous–homogeneous reactions. The Pt/silica catalysts appear to mature with use. Catalysed combustions take place, as expected, at far lower temperatures and with smaller activation energies than the homogeneous reactions. The role of added or intermediate (i.e. produced by alkane partial oxidation or steam reforming) H₂ in accelerating and lowering the temperatures of catalysed alkane combustions and hence minimising NO_x emission is considered with regard to the dispersion of the Pt, as is bifurcative–hysteretic combustion in the catalysed reaction, prevalent for CO, but less certain for H₂ or alkanes. CO decelerates the catalysed combustion of hydrogen on supported Pt (and may also do this for alkane combustion). Whether the acceleration due to intermediate H₂ in alkane combustion exceeds the deceleration due to intermediate CO remains to be seen, but it may be that the water–gas shift reaction moves the advantage to H₂. Further study by in situ methods will be needed to optimise and understand this coupling so that it can be used to maximise efficient alkane-catalysed combustion with minimum NO_x production. This should also lead to higher turnover numbers (which are at present quite low for propane-catalysed combustion).