Simultaneous MS-IR Studies of Surface Formate Reactivity Under Methanol Synthesis Conditions on Cu/SiO2

Journal Article · Tue Jun 09 04:00:00 EDT 2009 · Topics in Catalysis, 52(10):1440-1447

DOI:https://doi.org/10.1007/s11244-009-9320-3· OSTI ID:963198

Yang, Yong; Mims, Charles A; Disselkamp, Robert S; Peden, Charles HF; Campbell, C T

The coverages and surface lifetimes of copper-bound formates on Cu/SiO2 catalysts, and the steady-state rates of reverse water-gas shift and methanol synthesis have been measured simultaneously by mass (MS) and infrared (IR) spectroscopies under a variety of elevated pressure conditions at temperatures between 140 and 160°C. DCOO lifetimes under steady state catalytic conditions in CO2:D2 atmospheres were measured by 12C – 13C isotope transients (SSITKA). The values range from 220s at 160°C to 660s at 140°C. The catalytic rates of both reverse water gas shift (RWGS) and methanol synthesis are ~100-fold slower than this formate removal rate back to CO2+1/2 H2, and thus they do not significantly influence the formate lifetime or coverage at steady state. The formate coverage is instead determined by formate’s rapid production / decomposition equilibrium with gas phase CO2+H2. The results are consistent with formate being an intermediate in methanol synthesis, but with the rate-controlling step being after formate production (for example, its further hydrogenation to methoxy). A 2-3 fold shorter life time (faster decomposition rate) was observed for formate under reactions conditions when both D2 and CO2 are present than in pure Ar or D2+Ar alone, attributed to effects of coadsorbates (produced in D2 and CO2) on adsorbed formate reaction pathways. The carbon which appears in the methanol product spends a longer time on the surface than the formate species, 1.8 times as long at 140°C. The additional delay on the surface is attributed in part to readsorption of methanol on the catalyst, thus obscuring the mechanistic link between formate and methanol.

• 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: 963198
• Report Number(s): PNNL-SA-62339; 16696; 30209
• Journal Information: Topics in Catalysis, 52(10):1440-1447, Journal Name: Topics in Catalysis, 52(10):1440-1447 Journal Issue: 10 Vol. 52
• Country of Publication: United States
• Language: English

Related Subjects

10 SYNTHETIC FUELS
CARBON
CATALYSTS
Environmental Molecular Sciences Laboratory
FORMATES
FTIR
HYDROGENATION
LIFETIME
METHANOL
PRODUCTION
REMOVAL
SSITKA
SYNTHESIS
TRANSIENTS
WATER GAS
copper silica catalysts
methanol synthesis
water-gas shift