LAUSR

Abstract A method for quantifying the surface coverage of adsorbate species for reactions at high pressure and high temperature is presented. Methanol was synthesized from CO 2 /CO/H 2 (3/29/68) at 523 K and 50 bar on Raney Cu, which yielded a turnover frequency (TOF) per Cu surface atom of (6.22 ± 1.04) × 10 –3  s –1 . Rapid quenching by submerging the catalytic reactor in ice water during operation allowed the formate surface coverage on Cu (θ Cu-HCOO ) at reaction conditions to be determined in a subsequent temperature programmed desorption experiment. This yielded θ Cu-HCOO  = 0.071 ± 0.012 ML and a corresponding TOF per adsorbed HCOO of 0.088 ± 0.021 s –1 . CO 2 was essentially observed to be the exclusive source of methanol formation over Raney Cu, as the CO in the syngas could be replaced by N 2 without impact on the methanol formation rate. Based on this observation and the considerable support in the literature for a CO 2 -pathway via surface formate on Cu the TOF per surface formate species should represent the true rate of the catalytic cycle in Cu-catalyzed methanol synthesis. Temperature programmed hydrogenation of Raney Cu and unsupported Cu after quenching during high-pressure operation did not indicate a presence of oxygen species (O or OH) on the working Cu surface. Graphic Abstract