Quantitative Determination of the Catalytic Activity of Bulk Metal Oxides for Formic Acid Oxidation

• Published in: Journal of catalysis 2002-09, Vol.210 (2), p.241-254
• Main Authors: Fein, David E., Wachs, Israel E.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.2002.3683

The dissociative chemisorption of formic acid, HCOOH, to surface formate species, HCOO-M, on metal oxide catalysts was examined. The chemisorption studies reveal an average of ∼5–6 μmol/m 2 of active surface sites for many of the metal oxide catalysts. From TPD experiments, the decomposition temperatures of the surface formate ( T p) were found to vary from 88 to 313°C. The turnover frequency (TOF) values for formic acid oxidation were found to vary over 11 orders of magnitude (10 −3–10 8 s −1) at 250°C. No correlations were found between (i) H 2-TPR onset temperatures and the enthalpies of formation of bulk metal oxides (−Δ H f), (ii) TOFs and H 2-TPR onset temperatures, or (iii) TOFs and the isotopic dioxygen exchange rates with the metal oxide lattice oxygen. Weak inverse correlations were found for both TOFs and catalytic activities versus −Δ H f. A strong inverse relationship was found between the TOFs and the surface formate decomposition temperatures, supporting the assertion that the rate-determining step during formic acid oxidation is the decomposition of the surface formate intermediate.