Multicomponent oxide catalysts for the oxidation of methanol to formaldehyde

Abstract

The activity and selectivity of multicomponent oxide catalysts containing Co, Ni, Fe and Bi molybdates have been studied by a gradientless flow-circulation method. The unsupported (K₁ and K₂) and silica-supported (K₃) catalysts, some of them promoted with phosphorus and thallium (K₂ and K₃) have been characterized by X-ray diffraction, infrared spectroscopy, Mössbauer spectroscopy, surface area and porous structure measurements. On the investigated catalysts the selectivity towards the oxidation of methanol to formaldehyde remains extremely high over a wide temperature interval (350–390°C). Significant difference in thermal stability of the catalysts during exploitation has been observed and attributed to the presence of a support and promoters. The relative change in principal kinetic parameters of Si-supported and P- and T1-promoted catalyst (K₃) and of the unsupported catalysts, but promoted with P and T1 (K₂) was about 5–10% for 60 days, while with the unsupported catalyst without promoters (K₁) the yield of formaldehyde decreased by about 30% during 80 h. The more stable activity of the catalyst K₂ and K₃ is associated also to some extent with the stabilizing role of the support and the promoters.