Development of an active, selective and durable water-gas shift catalyst for use in membrane reactors

• Rh/La2O3 decayed on stream due to its high basicity while Rh/La2O3·SiO2 was very stable (forms CH4).
• The Pt/La2O3·SiO2 catalysts formed <0.1% of CH4 and neither carbonaceous nor graphitic residues.
• On a gram of Pt basis, the most active catalyst has a Pt load of 0.1 wt% (between 0.02 and 1.2%).
• Using the catalyst with 0.1 wt% Pt was possible to obtain a CO conversion of 96% and a H2 recovery of 88%.

Rh(0.6%)/La2O3 and Rh(0.6%)/La2O3(27 wt%)·SiO2were assayed for the WGS reaction at 673 K and 1 atm. They were both more active than industrial Cr-Fe based catalysts. Rh(0.6%)/La2O3 was the most active but it progressively deactivated. To investigate its deactivation and the stability of the Rh(0.6%)/La2O3(27 wt%)·SiO2, the WGS reaction was carried out in a DRIFTS cell in operando mode. The deactivation of the former was due to the strong adsorption of intermediate oxygenates. Another disadvantage of the Rh formulations was their methanation activity. Therefore, a series of formulations containing 0.1 wt% through 1.2 wt% Pt supported on La2O3(27 wt%)·SiO2 were synthesized and catalytically evaluated in a fixed-bed reactor. The activity, methane formation and stability were carefully checked. The fresh and used catalysts were characterized through a battery of techniques including XRD, LRS and XPS. The Pt(0.1 wt%) formulation resulted the most active one per gram of platinum and negligible methanation occurred. It maintained the activity and selectivity after 155 h on stream. This catalyst was tested in a Pd-Ag membrane reactor to produce ultrapure H2 (<10 ppm of CO) that can be used to feed a low temperature PEM fuel cell. Comparing our results with those already published, it is concluded that our system is one of the best ones reported so far.

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