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Renewable H2 Production -- Aqueous Phase Reforming
 

Developed in 2002 by Dumesic group member Rupali Davda, Dr. Randy Cortright, and Professor Dumesic, Aqueous phase reforming has made possible the direct conversion of biomass to renewable energy sources. The process is a unique method that produces hydrogen from a wide range of oxygenated compounds, such as ethylene glycol, biomass-derived glycerol, sugars and sugar-alcohols. The APR system generates hydrogen from aqueous solutions of these oxygenated compounds in a single step reactor process compared to the three or more reaction steps required for hydrogen generation via conventional processes that utilize non-renewable fossil fuels.

Running this reaction in the aqueous-phase produces hydrogen at very low CO concentrations due to more favorable water-gas shift thermodyamics.  Additionally, less energy is required since the vaporization of water is no longer necessary. Removing water and running in the vapor phase leads to a product stream of CO and hydrogen which can be used as syngas for the Fischer-Tropsch process

The process has spawned multiple journal publication, several patents, and the formation of a company, Virent. Virent is dedicated to the commercial development and retail of small and large scale applications of the APR process.

 

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Raney Nickel-Tin Catalyst for Renewable H2 Production

While Ni-based catalysts produce large amounts of methane from APR of oxygenated hydrocarbons, we have discovered that the addition of Sn to Ni decreases the rate of methane production, while still maintaining high rates of H2 production.  A Raney Ni-Sn catalyst was synthesized that exhibited high activity and selectivity for production of H2, with values comparable to Pt based catalysts.

Raney Ni-Sn process description process overview

 

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Liquid Alkanes from APR of Biomass-derived Carbohydrates

Recently, our APR process has been modified to produce alkanes from biomass-derived sugars.  Alkanes ranging from C1 to C6 can be produced by aqueous phase dehydration/hydrogenation (APD/H) of sorbitol (hydrogenated glucose) by a bi-functional pathway. Sorbitol is repeatedly dehydrated by a solid acid(SiO2-Al2O3) or a mineral acid (HCl) catalyst and then hydrogenated on a metal catalyst (Pt or Pd). The biorefining of sugars to alkanes plus CO2 and water is an exothermic process in which the products retain approximately 95 % of the heating value and only 30 % of the mass of the reactant. Larger liquid alkanes ranging from C7-C15, which could be used as a premium, sulfur free diesel fuel, can be produced by APD/H of larger carbohydrate-derived molecules.

 

 

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CO oxidation via Aqueous Polyoxometalates and Gold Catalysts

 

We are focusing on studying the CO oxidation over gold catalysts using aqueous solutions of polyoxometalates. The POMs used are strong oxidation agents which facilitate CO oxidation by liquid water at room temperature. High rates of CO oxidation were achieved at room temperature using aqueous solutions of polyoxometalates over carbon-supported gold catalysts. Gold catalysts has also showed higher rates for preferential oxidation of CO over hydrogen gas in hydrogen rich environments compared to other metal catalysts (i.e. Pt, Pd, Ir). Conventional processes for CO conversion often involve the use of Pt or Pt-alloy catalysts, which are expensive. These also compete with fuel cell electrodes for the limited supply of this precious metal, compared with the abundant holdings of gold in the world. The observed rates are faster than conventional processes operating at 500 K or higher for conversion of CO with water to produce hydrogen and carbon dioxide (via the water-gas shift, WGS). By eliminating the WGS reaction, we remove the need to transport and vaporize liquid water in the production of energy for portable applications. This process can utilize CO-containing gas streams from catalytic reforming of hydrocarbons to produce an aqueous solution of reduced polyoxometalate compounds that can be used to generate power. The reduced polyoxometalate can be re-oxidized in fuel cells containing simple carbon anodes.

 

 


SEM of Au nanotube catalyst

 

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Low Temperature Water Gas Shift Reaction

The water gas shift reaction (WGSR), CO + H2O --> CO2 + H2 is an industrially important route to H2 production and plays an important role in many current technologies such as methanol synthesis, methanol steam reforming, ammonia synthesis, coal gasification, as well as fuel cell technology. Using quantum chemical methods such as Density Functional Theory (DFT), we are studying this reaction extensively on a series of late transition metals. These studies have shown that WGSR proceeds via formation of carboxyl intermediate on the catalytically important materials such as Cu, Pt, Au and Ag; whereas the traditionally accepted redox mechanism is likely to be dominant only on Pd, Rh, Ir, Ru, Co and Ni. This study has also helped us to determine the characteristics that define a good WGS catalyst, and hence allowed us to screen for potentially active WGS catalysts.

Results from recent experimental studies have shown that supported gold catalysts hold strong promise for a number of low temperature reactions. Of particular interest are the application of Au for the low temperature water-gas shift (WGS) reaction and the preferential oxidation of CO in the presence of H2 (PROX). WGS is an important step in the production of H2 via the steam reforming of hydrocarbons and PROX is a key reaction for feeding low temperature fuel cells with clean hydrogen streams since the PEM fuel cell anodes get poisoned even by low levels (ppm) of CO. The enhanced activity of Au catalysts for these reactions at low temperatures still remains controversial.


 

 

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