Search

The oxidative coupling of methane was studied by cofeeding methane and oxygen over a series of titanate catalysts. Many of the titanate catalysts were good combustion catalysts and had poor hydrocarbon selectivities. Calcination and reduction pretreatments were shown to affect the activity of some catalysts: while they had little influence on other titanate catalysts. The lanthanum titanate catalyst had the best hydrocarbon selectivities of the titanates studied, exhibiting methane conversions of 20% and hydrocarbon selectivities of better than 50% for a variety of operating conditions. The effect of operating conditions were studied, and there appears to be an optimum to achieve high yields of ethane and ethylene. The catalyst was studied over a seventy-two hour period and showed very little change with time-on-stream. The lanthanum titanate catalyst activated methane at much lower temperatures than other catalysts; however, its hydrocarbon selectivity was poorer at lower temperatures.

Metal-support and metal-promoter interactions have been studied by x-ray photoelectron spectroscopy. Decoration of the metal particles by metal oxide species is observed for Pd in contact with La 2 O 3 , Pt in contact with WO 3 , and Pt in contact with TiO 2 . In every case where decoration occurs, there is also a negative shift in the apparent binding energy of the core electron levels of the metal after reduction in hydrogen at elevated temperatures. The shift can be as great as −0.7 eV relative to the bulk foil value. Charging of insulating catalyst powders makes it difficult to establish the binding energy reference level within the sample. However, analysis of the charging behavior suggests that the negative shift may result from a change in the electronic properties of the metal surface.