Surface-Bound Intermediates in Low-Temperature Methanol Synthesis on Copper. Participants and Spectators
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Washington, Seattle, WA (United States)
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Univ. of Washington, Seattle, WA (United States)
- 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 Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1228347
- Report Number(s):
- PNNL-SA-112923; 48593; KC0302010
- Journal Information:
- ACS Catalysis, Vol. 5, Issue 12; ISSN 2155-5435
- Country of Publication:
- United States
- Language:
- English
Similar Records
Unimolecular and bimolecular formic acid decomposition routes on dispersed Cu nanoparticles
Catalytic Links Among the Water-Gas shift, Water-Assisted Formic Acid Decomposition, and Methanol Steam Reforming Reactions over Pt PromotedTthoria