Catalyst preferential oxidation

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. 

In Sn/V/Nb/Sb/O catalysts, different compoimds form (10) mtile Sn02 (also incorporating Sb, Sb/Nb mixed oxide and non-stoichiometric mtile-type V/Nb/Sb/O the latter segregates preferentially at the smface of the catalyst. Tin oxide (cassiterite) provides the matrix for the dispersion of the active components therefore, a variation of the value of x in Sn/V/Nb/Sb x/0.2/1/3 catalysts imphes a... 

Oxidation of Aldonic Acids. Preferential oxidation of the secondary alcoholic group adjacent to the carboxyl group in sugar acids or aldonic acids such as L-gulonic acid (XXV) can be carried out with chromic acid12 or with chlorates in the presence of a vanadium catalyst.13... 

The main unit is the catalytic primaiy process reactor for gross production, based on the ATR of biodiesel. After the primary step, secondary units for both the CO clean-up process and the simultaneous increase of the concentration are employed the content from the reformated gas can be increased through the water-gas shift (WGS) reaction by converting the CO with steam to CO and H. The high thermal shift (HTS) reactor is operating at 575-625 K followed by a low thermal shift (LTS) reactor operating at 475-535 K (Ruettinger et al., 2003). A preferential oxidation (PROX) step is required to completely remove the CO by oxidation to COj on a noble metal catalyst. The PROX reaction is assumed to take place in an isothermal bed reactor at 425 K after the last shift step (Rosso et al., 2004). 

As an application of Pt nanowires in heterogeneous catalysis, we performed preferential oxidation (PROX) of CO as a test reaction [32]. The PROX reaction is useful for PEM fuel cells for the selective removal of contaminating CO from hydrogen gas, because CO works as a strong catalyst poison for Pt electrode catalysts (Figure 15.24). H2 produced in steam-reforming and the water-gas shift reaction needs further to be purified in the PROX reaction to selectively oxidize a few% CO towards inert CO2 in a H 2-rich atmosphere, to reduce the CO content to <10ppm. Under the PROX conditions, the facile oxidation of H2 to H2O may also occur, thus the catalyst selectivity for CO oxidation over H2 oxidation is an... 

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

Data reported in the present work demonstrate that the degree of crystallinity and the acid properties are related the amount of present at the surface of VPP. When the VPP is not fully equilibrated, and hence may contain discrete amounts of it is more selective to MA and less to PA. The reason is that in oxidized catalysts, the olefmic intermediate is preferentially oxidized to MA, rather then being subjected to the acid-catalyzed condensation with a second unsaturated molecule, to yield the precursor of PA. When instead the catalyst is more crystalline, and hence it does contain less oxidized V sites, its surface acid properties predominate over O-insertion properties, and the catalyst becomes more effective in PA formation. In this case, the selectivity to PA at 50% n-pentane conversion becomes comparable to that one of MA. 

Promoters. - Many supported vanadia catalysts also possess secondary metal oxides additives that act as promoters (enhance the reaction rate or improve product selectivity). Some of the typical additives that are found in supported metal oxide catalysts are oxides of W, Nb, Si, P, etc. These secondary metal oxide additives are generally not redox sites and usually possess Lewis and Bronsted acidity.50 Similar to the surface vanadia species, these promoters preferentially anchor to the oxide substrate, below monolayer coverage, to form two-dimensional surface metal oxide species. This is schematically shown in Figure 4. 

Preferential Oxidation (PROX) of CO in Excess H2 on Novel Metal Catalysts... 

Table 3.1 shows the catalytic performance of supported Au catalysts for the preferential oxidation (PROX) of CO in H2 together with the actual reaction conditions and targeted performances. Au/A1203 [61-63], Au/Mn203 [58], Au/ Fe203 [54, 60, 61, 64—66] and Au/Ce02 [54, 60-62, 67-70] have been reported to... 

Figure 2.81 Network of 27 catalyst beds (five for pre-reforming, nine for reforming, nine for catalytic combustion to supply the heat, two for water-gas shift and two for preferential oxidation) and of 20 heat exchangers [128]...

Wash coats made of various source aluminas were prepared by applying this procedure (Figure 2.96) [147]. The catalysts obtained after subsequent impregnation were applied to methanol steam reforming [25, 28], propane steam reforming [52], water-gas shift [84] and preferential oxidation [89], to name but a few reaction systems. 

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