Surface-Bound Intermediates in Low-Temperature Methanol Synthesis on Copper. Participants and Spectators

Journal Article · Tue Nov 03 04:00:00 EST 2015 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.5b02060· OSTI ID:1228347

Yang, Yong ^[1]; Mei, Donghai ^[2]; Peden, Charles H.F. ^[2]; Campbell, Charles T. ^[3]; Mims, Charles A. ^[4]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Washington, Seattle, WA (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
3. Univ. of Washington, Seattle, WA (United States)
4. Univ. of Toronto, ON (Canada)

The reactivity of surface adsorbed species present on copper catalysts during methanol synthesis at low temperatures was studied by simultaneous infrared spectroscopy (IR) and mass spectroscopy (MS) measurements during “titration” (transient surface reaction) experiments with isotopic tracing. The results show that adsorbed formate is a major bystander species present on the surface under steady-state methanol synthesis reaction conditions, but it cannot be converted to methanol by reaction with pure H₂, nor with H₂ plus added water. Formate-containing surface adlayers for these experiments were produced during steady state catalysis in (a) H₂:CO₂ (with substantial formate coverage) and (b) moist H₂:CO (with no IR visible formate species). Both these reaction conditions produce methanol at steady state with relatively high rates. Adlayers containing formate were also produced by (c) formic acid adsorption. Various "titration" gases were used to probe these adlayers at modest temperatures (T = 410-450K) and 6 bar total pressure. Methanol gas (up to ~1% monolayer equivalent) was produced in "titration" from the H₂:CO₂ catalytic adlayers by H₂ plus water, but not by dry hydrogen. The decay in the formate IR features accelerated in the presence of added water vapor. The H₂:CO:H₂O catalytic adlayer produced similar methanol titration yields in H₂ plus water but showed no surface formate features in IR (less than 0.2% monolayer coverage). Finally, formate from formic acid chemisorption produced no methanol under any titration conditions. Even under (H₂:CO₂) catalytic reaction conditions, isotope tracing showed that pre-adsorbed formate from formic acid did not contribute to the methanol produced. Although non-formate intermediates exist during low temperature methanol synthesis on copper which can be converted to methanol gas by titration with pure H₂ plus water in sufficient quantities for that intermediate to be observable by IR, formate itself is only a "spectator" in this reaction and gives no observable methanol upon any titration we performed with H₂ or H₂ plus water.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1228347
• Report Number(s): PNNL-SA-112923; 48593; KC0302010
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 12 Vol. 5; ISSN 2155-5435
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory
copper catalyst
formate intermediate
methanol synthesis
reaction mechanism