Reaction of Formic Acid on Zn-Modified Pd(111)
- PDF / 482,760 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 69 Downloads / 233 Views
Reaction of Formic Acid on Zn-Modified Pd(111) Eseoghene Jeroro Æ John M. Vohs
Received: 3 February 2009 / Accepted: 23 March 2009 / Published online: 27 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The decomposition of formic acid on Zn/Pd(111) was studied using Temperature Programmed Desorption and High Resolution Electron Energy Loss Spectroscopy. On Pd(111), HCOOH decomposes via both dehydration and dehydrogenation pathways to produce CO, CO2, H2 and H2O. Small amounts of Zn (\0.1 mL) incorporated the Pd(111) surface were found to increase the stability of formate species and alter their decomposition selectivity to favor dehydrogenation, resulting in an increase in CO2 production. This difference in reactivity appears to be caused by relatively long range electronic interactions between surface Pd and Zn atoms and may be important in Pd/ZnO methanol steam reforming catalysts which exhibit high selectivities to CO2 and H2. Keywords
ZnO Pd Formic acid
1 Introduction The production of hydrogen fuel is an essential step in the operation of most fuel cell systems and alcohols have been proposed as possible hydrogen sources since they can be produced from bio-renewable resources. For alcohols to be a viable hydrogen source, however, requires highly active catalysts that allow them to be steam reformed into H2 and CO2 under relatively mild conditions. Pd supported on ZnO has emerged as a promising catalyst for this purpose and exhibits high activity and selectivity for reforming of both methanol
E. Jeroro J. M. Vohs (&) Department of Chemical and Bimolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104-6393, USA e-mail: [email protected]
and ethanol [1, 2]. It also does not suffer from some of the drawbacks of the other commonly used catalyst, Cu/ZnO, which is pyrophoric once reduced and prone to activity loss due to sintering [3, 4]. From a fundamental perspective, Pd/ZnO is also very interesting since it exhibits[95% selectivity for the production of CO2 and H2 [1, 2] during steam reforming of methanol in spite of the fact that Pd on most other supports produces almost exclusively CO and H2 [1]. Multiple studies have shown that the unique reactivity of the Pd/ZnO catalyst can be attributed in large part to the formation of a PdZn alloy under reaction conditions [5, 6]. The mechanism by which Zn alters the reactivity of the Pd, however, is only starting to be understood [7–12]. Since the observed CO2 selectivity during the steam reforming of methanol on Pd/ZnO exceeds the equilibrium selectivity obtainable by the water gas shift (WGS) reaction, a pathway involving the dehydrogenation of methoxide to CO followed by WGS to produce CO2 can be ruled out [1, 13]. In light of this, it has been proposed that the most likely pathway for the methanol steam reforming reaction is the partial dehydrogenation of adsorbed methoxide to form formaldehyde or formyl species that react with water or hydroxyl groups to produce formate which ultimately decomposes to CO2 and H2 as shown in
Data Loading...
