Extending surface science studies to industrial reaction conditions: mechanism and kinetics of methanol oxidation over silver surfaces

The selective oxidation of CH3OH to H2CO over the noble metals Cu, Ag and Au represents one of the oldest industrial catalytic technologies dating back to the 1880s [1,2] and also the first non-Pt based catalytic industrial process. Initially, the catalyst employed for methanol oxidation was metallic Cu and subsequent research three decades later comparing the noble different metal catalysts found that Ag was the most efficient catalyst for this reaction. The commercial Ag catalysts are unsupported and are in the form of pure needles, wires or gauzes and are of very high purity (99.999% Ag) with very low surface areas (BET 0:1 m/g). Currently, more than 50% of the world s H2CO is manufactured employing metallic Ag catalysts. Bulk mixed iron-molybdate catalysts account for the remaining H2CO production and commercially introduced in the middle of the 20th century. The advantage of the Ag-based technology is that it is a very flexible and simple process to start, operate (adiabatic reaction conditions), shut down and change the catalyst. Analogous alcohol oxidation reactions over the noble metal catalysts are also employed in the chemical industry to synthesize higher molecular weight aldehydes such as C10–C20 fragrances. The proposed reaction mechanism of methanol oxidation over Ag catalysts has also undergone significant changes over the years and has attracted much attention in the past 25 years by many leading surface science and catalysis research groups (more than 250 publications, which corresponds to an average of 10 papers/year). The initial proposed mechanism consisted of two sequential steps: