Abstract
In industry, one of the main catalysts typically employed for the selective oxidation of methanol to formaldehyde is a multi-component oxide containing both bulk Fe2(MoO4)3 and excess MoO3. It is thought that the excess MoO3 primarily acts to replace any molybdenum lost through sublimation at elevated temperatures, therefore preventing the formation of an unselective Fe2O3 phase. With both oxide phases present however, debate has arisen regarding the active component of the catalyst. Work here highlights how catalyst surfaces are significantly different from bulk structures, a difference crucial for catalyst performance. Specifically, Mo has been isolated at the surface as the active surface species. This leaves the role of the Fe in the catalyst enigmatic, with many theories postulated for its requirement. It has been suggested that the supporting Fe molybdate phase enables lattice oxygen transfer to the surface, to help prevent the selectivity loss which would occur in the resulting oxygen deficit environment. To assess this phenomenon in further detail, anaerobic reaction with methanol has been adopted to evaluate the performance of the catalyst under reducing conditions.
Highlights
The selective oxidation of methanol to formaldehyde is a fundamental industrial reaction, reflected by its global demand in excess of 30 million tonnes per annum [1]
Low-energy ion scattering (LEIS) analysis of the outermost surface layer revealed that the molybdate catalysts possessed a monolayer of surface MoOx species, onto which surface CH3 OH and CH3 O were shown to be present by IR spectroscopy
The results revealed crucial regarding solid‐state kinetics of theabsorption processes,spectroscopy whilst (XAS)
Summary
The selective oxidation of methanol to formaldehyde is a fundamental industrial reaction, reflected by its global demand in excess of 30 million tonnes per annum [1]. Since 1931 [2], the most commonly adopted catalyst employed industrially is an iron molybdate based catalyst, Fe2 (MoO4 ) , to which an excess of MoO3 is added to the chemical composition This mixed oxide catalyst is considered by many to be a more economical means of effecting partial oxidation of methanol, compared to other oxides and Ag catalysts. The role of the excess crystalline MoO3 was identified to replenish the surface MoOx lost by volatilization during methanol oxidation. Work exploits this theory, with the challenging aim to unravel the nature of the active site in commercial Fe2 (MoO4 ) catalysts, through use of model.
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