Improved Reformate-Tolerant Catalysts

In recent times, efforts have been made to optimize PtRu tolerance through the addition of third and fourth metals, as well as to identify alterative Pt-based catalysts with much greater reformate tolerance, particularly at much higher CO levels. Many of fhe reporfed sfudies are concerned with CO rather than reformate tolerance, and few long-ferm sfabilify measurements have been reported. 

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Although great efforts have made to improved reformate-tolerant catalysts, no intrinsic reformate-tolerant catalysts have yet been discovered. The FtMo system appears to offer the greatest possibilities, especially at higher CO concentrations and at higher temperatures. However, the corrosion sensitivity of Mo over time needs to be addressed before these catalysts become practical systems. 

Carbon-supported Pt can also be used as the anode catalyst. However, this requires pure H2. Contaminants such as carbon monoxide (CO) poison the catalyst, because CO can strongly adsorb on Pt, blocking the catalytic sites and reducing platinum s catalytic activity. In H2 produced from the reforming of other fuels, CO is always present. Thus, to improve contaminant tolerance, carbon-supported PtRu was developed and now is always used as the anode catalyst. Ru can facilitate the oxidation of CO, releasing the catalytic sites on Pt through the following reactions ... 

A proprietary sulfur-tolerant catalyst developed by InnovaTek can reform natural gas, gasoline, and diesel fuels without need for prior sulfur removal, thereby greatly improving the prospects for commercialization of fuel cell technology. 

Cobalt is used to promote CO oxidation in reformers [284, 285], suggesting PtCo alloys may be useful catalysts for H2 oxidation in the presence of CO. PtCo alloys have been proposed as improved methanol oxidation catalysts [286] because cobalt may assist with CO removal (CO is an intermediate in meflianol electrooxidation) through a mechanism analogous to the PtRu bifunctional mechanism. PtCo alloys have also been studied as improved ORR catalysts [200, 287, 288]. In addition to their improved ORR kinetics, these alloys have been shown to be more tolerant to methanol crossover in direct methanol fuel cells (DMFCs), again possibly through improved CO removal kinetics [289]. However, Stevens et al. [235] observed no impact on CO-stripping with the addition of eobalt to Pt, and explained this as due to surface cobalt dissolving away. 

One particular application for which supported Au catalysts may find a niche market is in fuel cells [4, 50] and in particular in polymer electrolyte fuel cells (PEFC), which are used in residential electric power and electric vehicles and operate at about 353-473 K. Polymer electrolyte fuel cells are usually operated by hydrogen produced from methane or methanol by steam reforming followed by water-gas shift reaction. Residual CO (about 1 vol.%) in the reformer output after the shift reaction poisons the Pt anode at a relatively low PEFC operating temperature. To solve this problem, the anode of the fuel cell should be improved to become more CO tolerant (Pt-Ru alloying) and secondly catalytic systems should be developed that can remove even trace amounts of CO from H2 in the presence of excess C02 and water. 

A,B-site modified LaNi03 and LaCo03 were demonstrated to be active autothermal reforming catalysts and appear to be structurally stable under the reducing reaction conditions. Sulfur tolerance is still an issue based on the rapid decrease in the H2 concentration in the reformate when reforming sulfur-containing fuels. Future work will focus on improving the activity and the sulfur tolerance of these perovskite catalysts. 

The tolerance of Ni catalysts to carbon-induced deactivation in hydrocarbon steam reforming and partial oxidation reactions can be significantly improved by impregnating Ni with small amounts of Sn (0.2-1 wt% with respect to Ni for Ni particles with the diameter between 30 and 200 nm). " Based on DFT calculations, it was... 

Ferrandon, M., Mawdsley, J., and Krause, T. (2008) Effect of temperature, steam-to-carbon ratio, and alkali metal additives on improving the sulfur tolerance of a Rh/La-Al203 catalyst reforming gasoline for fuel cell applications. Appl. Catal. A Gen., 342, 69. 

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