Preferential Oxidation of CO in H₂ by Aqueous Polyoxometalates over Metal Catalysts

Abstract

Production of H 2 for fuel cells is usually accomplished by a multistep process, which starts with catalytic reforming of hydrocarbons [1] or oxygenated hydrocarbons over metal catalysts [2,3] to produce a mixture of H 2 , CO, and CO 2 . These reformate gases are subsequently treated by several steps, such as water-gas shift (WGS) (CO + H 2 O!CO 2 + H 2 ) [4,5] and preferential oxidation of CO in the H 2 -rich gas stream (PROX; CO + 1/2 O 2 !CO 2 ), [6,7] for applications involving proton-exchange membrane (PEM) fuel cells, this oxidation of CO is necessary owing to the strong poisoning effects of CO on Pt-based anodes.[8] While these methods for removing CO from H 2 gas stream are well established, they suffer from several limitations. For example, the WGS reaction is slow at the low temperatures (e.g., 500 K) required to achieve favorable thermodynamics for this reaction, [9] and PROX requires the injection of O 2 (or air) into the H 2 gas stream and consumes a fraction of the H 2 as well. Moreover, these processes for CO conversion often involve the use of platinum or platinum-alloy catalysts, which are expensive and compete with fuel-cell electrodes for the limited supply of this precious metal, compared with the abundant holdings of gold in the world.[10]Recently, we reported the discovery of a room-temperature process for production of electrical energy using a fuel cell containing a carbon anode and operating with an aqueous solution of a polyoxometalate (POM) compound that had been reduced with pure CO over gold-nanotube catalysts. [11] This process for the oxidation and utilization of CO involves the reaction of CO and liquid water with a reducible POM, such as [H 3 PMo 12 O 40 ], which serves as an oxidizing agent for reaction of CO with liquid water and as an energy-storage agent for electrons; the process takes advantage of the high catalytic activities of gold for CO oxidation, [12][13][14] especially in the presence of liquid water, as shown experimentally using gold-nanotube membrane catalysts [15] and as predicted by density functional theory calculations. [16,17] A representative

Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering

“…[124][125][126] The overall reaction (eq 6) involves oxidation of CO and water to CO 2 and protons with polyoxyometalates (POM), such as H 3 PMo 12 O 40 , in the presence of a gold catalyst. The aqueous solution of reduced POMs and protons can then be used to produce electricity at the anode of a PEM fuel cell.…”

Preferential Oxidation of CO in H2 by Aqueous Polyoxometalates over Metal Catalysts

“…[11] This process for the oxidation and utilization of CO involves the reaction of CO and liquid water with a reducible POM, such as [H 3 PMo 12 O 40 ], which serves as an oxidizing agent for reaction of CO with liquid water and as an energy-storage agent for electrons; the process takes advantage of the high catalytic activities of gold for CO oxidation, [12][13][14] especially in the presence of liquid water, as shown experimentally using gold-nanotube membrane catalysts [15] and as predicted by density functional theory calculations. [16,17] A representative…”

“…The aqueous solution of protons and reduced POM formed in this reaction can be delivered to a PEM fuel cell to generate electrical energy by using a carbon anode, thereby regenerating the POM in its initial oxidized state. [11] The POM species thus functions as a redox shuttle, thereby eliminating the need to convert CO with H 2 O into gaseous H 2 and CO 2 for the production of electrical energy.…”

Controlling the Catalytic Activity of Platinum‐Monolayer Electrocatalysts for Oxygen Reduction with Different Substrates

“…[4,5] Electrocatalytic oxygen reduction, the reaction at fuelcell cathodes, has been the focus of attention because of its slow kinetics and because of the need for better electrocatalysts with decreased platinum content. [6][7][8] Herein we report the results of a study on the electrocatalytic activity for the oxygen reduction reaction (ORR) of platinum monolayers supported on Au(111), Rh(111), Pd(111), Ru(0001), and Ir(111) surfaces in a 0.1m HClO 4 solution.…”