Energetics of methanol and formic acid oxidation on Pt(111): Mechanistic insights from adsorption calorimetry

Abstract

The catalytic and electrocatalytic oxidation and reforming of methanol and formic acid have received intense interest due to potential use in direct fuel cells and as prototype models for understanding electrocatalysis. Consequently, the reaction energy diagram (energies of all the adsorbed intermediates and activation energies of all the elementary steps) have been estimated for these reactions on Pt(111) by density functional theory (DFT) in several studies. However, no experimental measurement of these energy diagrams have been reported, nor is there a consensus on the mechanisms. Here, we use energies of key intermediates on Pt(111) from single crystal adsorption calorimetry (SCAC) and temperature programmed desorption (TPD) to build a combined energy diagram for these reactions. It suggests a new pathway involving monodentate formate as a key intermediate, with bidentate formate only being a spectator species that slows the rate. This helps reconcile conflicting proposed mechanisms.

Strategic examination of the classical catalysis of formic acid decomposition for intermittent hydrogen production, storage and supply: A review

“…The results revealed the increased catalytic activities as well as product (H 2 ) selectivity of the catalysts for FA [93]; these results are also supported by results obtained by other investigators [87,[94][95][96][97][98][99]. Catalyst-orientation can be in several categories including single crystals [100][101][102] and bulk forms [103], as supports/anchors [104][105][106], organic complexes of metals [107,108] and metallic salts [109]. Noble metals only have the capacity to catalyse the dehydrogenation step of formic acid decomposition while base metals and their oxides are useful for the dehydration and dehydrogenation steps [104]; this justifies the idea of catalyst-hybridization in order to take advantage of, as well as maximize the catalytic potential of each class/type of catalyst.…”

“…However, based on the work of Sanni et al [24], it is obvious that the Cu-tertiary amine system adopted, has the ability to overcome these odds since the dehydrogenation step induced by noble metalcatalysts takes advantage of the intermediate formates/complexes formed at the dehydrogenation stage [100,105]. According to Silbaugh et al [106] monodentate formate is a key intermediate product of formic acid decomposition that is further converted to bidentate formate; this reaction is reversible in nature which explains the tendency for reestablishing the system's equilibrium. The thermochemical analyses of the decomposition of HCOOH on sample-facets of Au, Ag, Co, Cu, Ni, Os, Pt, Pd, Rh and Ru catalysts have been investigated [18].…”

Misconceptions in the Exploding Flask Demonstration Resolved through Students’ Critical Thinking

“… Energy profile for complete catalytic combustion of CH 3 OH on Pt(111) based on refs ( 16 , 31 , and 32 ). …”

The Barrier for CO2 Functionalization to Formate on Hydrogenated Pt

“…Preadsorbed oxygen atoms on Pt increase the efficiency of formic acid decomposition by forming monodentate formate and OH*. − DCOO* subsequently converts into its more stable isomer, the bidentate formate, DCO*O* . Recently, single crystal adsorption calorimetry (SCAC) has been used to measure the heats of formation of both intermediates at an oxygen covered Pt(111) surface. , Furthermore, it is believed that while DCOO* can decompose to CO 2 , DCO*O* cannot; instead it converts to DCOO* . The barriers for CO 2 formation have been investigated earlier with molecular beam relaxation spectrometry (MBRS) on Pt(110); however in previous work no conclusions about the rate-determining step to the formation of CO 2 could be made.…”