Total methanol oxidation studied by MS-DRIFT operando and MES on bimetallic Au-Pd catalysts

Abstract

The mechanism of methanol oxidation was investigated by combining operando and modulation-excitation diffuse reflectance infrared spectroscopy (MES-DRIFT) over monometallic Au/CeO2-ZrO2(CZ) and Pd/CZ catalysts, and also over the corresponding Au-Pd bimetallic catalysts with Au:Pd ratios of 1:1, 3:1 and 10:1. Adsorbed intermediaries were identified spectroscopically on the support, e.g. methoxy, mono- and bidentate formate, carbonates, and possibly CO adsorbed on gold sites or Pd modified by Au. The catalytic activity was evaluated by mass spectrometry (MS) coupled to the exit of the reactor cell (DRIFT), observing that the reaction is favored over the bimetallic catalysts with respect to their monometallic counterparts, and furthermore showing the first ones a trend which follows their Au:Pd ratios being more active the ones with less gold. It is postulated that the region of the support close to the metal particle is active during the reaction and possibly charge transfer between Au and Pd could be the main reason for their synergetic effect on the reaction studied. The less energetically favorable step is the decomposition of formate groups.