CO preferential

A microchannel reactor for CO preferential oxidation was developed. The reactor was consisted of microchannel patterned stainless steel plates which were coated by R11/AI2O3 catalyst. The reactor completely removed 1% CO contained in the Ha-rich reformed gas and controlled CO outlet concentration less than Ippm at 130 200°C and 50,000h. However, CH4 was produced from 180"C and CO selectivity was about 50%. For high performance of present PrOx reactor, reaction temperature should be carefully and uniformly controlled to reach high CO conversion and selectivity, and low CH4 production. It seems that the present microchaimel reactor is promising as a CO removal reactor for PEMFC systems. 

Rosso, I., Galletti, C., Saraeeo, G., Garrone, E., Speeehia, V. 2004. Development ofAzeolites-supported noble-metal eatalysts for CO preferential oxidation H, gas purifieation for fuel eell. Appl Catal B 48 195-203. 

A further purification step is carried out through the CO preferential oxidation reaction, generally employing precious metal-based catalysts, mostly Pt [10-13]. 

The phase behavior of alloy nanoparticles may differ from that in the bulk due to the increased significance of surface effects. Ge and coworkers examined the heats of formation of Pt-Au nanoparticles up to 13 atoms and compared them to bulk heats of formation.For bulk systems they found the heats of formation of Pt-Au alloys were all small and positive indicating a tendency to phase separate at low temperatures. In contrast, the heats of formation of some of the alloy atom clusters were significantly negative indicating that alloy nanoparticles may readily form. The adsorption of CO on the Pt-Au nanoparticles was larger than that on the bulk surfaces, and CO preferentially adsorbs on Pt sites that are adjacent to Au atoms. 

Echigo, M., Shinke, N., Takami, S., Higashiguchi, S., Hirai, K., and Tabata, T. Development of residential PEFC cogeneration systems Ru catalyst for CO preferential oxidation in reformed gas. Catalysis Today, 2003, 84, 209. 

Ahluwalia, R.K., Zhang, Q., Chmielewski, D.J., Lauzze, K.C., and Inbody, M.A. Performance of CO preferential oxidation reactor with noble-metal catalyst coated on ceramic monolith for onboard fuel processing applications. Catalysis Today, 2005, 99, 271. 

In addition to the enhancement of the CO2 reduction rate, product selectivity can be changed by elevation of the CO2 pres sure. Pb and In electrodes, forming HCOO exclusively at 1 atm, yield CO preferentially at a low current density (1 rrtA cin ) in 0.5-M KHCO3 at 20 atm. The reaction scheme will be discussed in Section VI. 5. 

A similar case is likely to happen in 0.5 M KHCO3 aqueous solution under elevated pressures. Sakata et al. reported that an In electrode yields CO preferentially instead of HCOO at a low current density (1 mA cm ) under 20 atm." CO2 , adsorbed on the electrode with a higher coverage than under 1 atm, may react with CO2 molecules present abundantly in pressurized solution, forming CO as the major product. 

In a typical example, acetophenone is used as a solvent . Soluble Rh complex is added in an amount sufficient to produce a final concentration of 100-500 ppm, calculated as the metal. Excess phosphine is added, together with the olefinic substrate. The reaction is conducted at 70-120°C and about 1 MPa pressure of synthesis gas with a composition of either 1/1 or 3/1 H2/CO. Preferentially, the pressure is held constant by continuous introduction of the stoichiometric 1/1 Hj/CO until absorption ceases. 

Echigo M., Shinke N., Takami S. and Tabata T. 2004. Performance of natural gas processor for residential PEFC system using a novel CO preferential oxidation catalyst, J. Power Sour., 132, 29-35. 

In another work [58], the authors studied the influence of CO and CO2 (components always present in reforming reactions) on the permeation of hydrogen. Although concentration polarization is not a problem, at low temperatures CO preferentially absorbs on the Pd surface (as found for all kind of configurations) depleting the hydrogen permeation rate. 

X. Ouyang, R. S. Besser, Effect of reactor heat transfer limitations on CO preferential oxidation. / Power Sources 2004, 343, 39-46. 

Ceria-zirconia mixed oxide-supported metal nanoparticles are attractive catalysts in low-temperature WGS, CO preferential oxidation (PROX), or three-way catalysis. It was observed that after redox cycles (reduction at 1173K and then oxidation at 823 K), the reducibility of these catalysts was enhanced substantially, which greatly affected their catalytic performance. HAADF studies showed that the pyrochlore-type cation sublattice in the reduced Ce Zr O was retained in the fully oxidized mixed oxide with a Ce Zr Og stoichiometry as far as the oxidation temperature did not exceed 823 K. However, it is not clear whether compositional heterogeneity occurred at the atomic level in Ce Zr Og. Trasobares and coworkers addressed this issue by aberration-corrected STEM, atomic-resolution EELS mapping, and EELS image simulations [66], They synchronously acquired EELS and HAADE signals in... 

CO preferential oxidation (CO-PROX) has been investigated in order to remove the trace amounts of CO in H2 rich stream, as remaining traces of CO in H2 can easily poison the Pt based anode electrocatalyst of polymer electrolyte membrane fuel cells (PEMFC). 

In the PEFCs using reformed hydrogen as the anode fuel, trace amount of CO exists even after reforming and CO preferential oxidation (PROX) reactions, which also poiscms the Pt catalyst The chemisorbed CO is oxidized to CO2 by a hydroxyl functional group formed on other active sites of the Pt by chemical reaction with a water molecule (formulas (2) and (3)). 

Nikolaidis, G., Kolb, G Baier, T, Maier, W.F., Zapf, R., Hessel, V. and Lowe (2008) H. Kinetic study of CO preferential oxidation over Pt/Rh/y-Al203 catalyst in a microstructured recyde reactor. Cat. Today, submitted for publication. 

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