Mechanism of partial oxidation of methanol over molybdenum(VI) oxide as studied by temperature-programmed desorption

A Combined Multi-Technique In Situ Approach Used to Probe the Stability of Iron Molybdate Catalysts During Redox Cycling

“…These results therefore suggest that a Langmuir-Hinshelwood rather than a Mars-Van Krevelen type process is occurring at this stage. This is observation is important since it suggests that both mechanisms can operate in the catalyst depending on the exact conditions and may explain the different observations in previous works [22][23][24][25][26][27][28][29]. Further evidence for this 'dual' mechanism can also be found from the changes in formaldehyde production on switching from back from air to methanol.…”

“…Interestingly however, on switching to air we observed a large increase in the formaldehyde production. As there was no methanol being introduced, the source of formaldehyde is likely to be surface-bound methoxy species [25,70,71]. This sudden increase in formaldehyde production in the absence of Fe 2 (MoO 4 ) 3 suggests that in these circumstances, the oxygen necessary to complete the reaction cycle leading to formaldehyde formation must have come directly from the gas phase.…”

“…if Mo/Fe is not greater than 1.5), breakdown to oxides occurs [13,[15][16][17][18]: Many authors believe the redox process occurs via a Mars-Van Krevelen type mechanism, [14,[19][20][21]. This mechanism is supported by kinetic studies and experimental works indicating rapid diffusion of bulk oxygen to the catalyst surface [22][23][24][25][26][27]. However, some measurements indicate that the process can also be expressed using modified Langmuir-Hinshelwood kinetics (with and without oxygen participation) [28,29].…”

Catalysts for the Selective Oxidation of Methanol

“…Ab initio quantum mechanical calculations performed by Allison et al [44] supported a multistep mechanism involving reaction of methanol with dual-dioxo catalytic sites. Since these dual sites were shown to exist on the (010) face of MoO 3 ( Figure 14), this face was deemed as the reactive site [45]. However, this is not unanimously agreed, with several authors revealing that the (010) plane exhibits especially low saturation, and any methanol adsorption occurring does not contribute to formaldehyde production.…”

“…However, this is not unanimously agreed, with several authors revealing that the (010) plane exhibits especially low saturation, and any methanol adsorption occurring does not contribute to formaldehyde production. The role of this face is still under investigation for selective methanol oxidation [14,45]. study was informative not only in providing information regarding these reduced phases, but also in preliminary investigating the mechanisms occurring at the surface.…”