Hydrogen production from methanol decomposition over Pt/Al2O3 and ceria promoted Pt/Al2O3 catalysts
Introduction
There is a growing necessity to find alternative ways to produce energy with lower emissions of pollutants and higher efficiencies compared to internal combustion. One such option is the use of proton exchange membrane (PEM) fuel cell system. PEM fuel cells convert hydrogen gas into useful electric power with an efficiency that is not limited by thermodynamics and the only by product is water [1], [2]. Due to current infrastructure, storage technology and safety concerns, hydrogen gas cannot be stored on-board in adequate amounts for mobile applications. On demand reforming of liquid hydrocarbons to produce hydrogen is seen as an attractive means of providing the necessary hydrogen to the fuel cell. With the exception of formic acid, methanol is the easiest hydrocarbon to reform. On board methanol reforming has a couple of advantages over other potential fuels: unlike gasoline or diesel fuel, liquid methanol can be readily produced from biomass, it is easily adaptable to the current infrastructure, it is easily transported and stored, and finally it has a high hydrogen density [3], [4], [5]. The most basic way to generate H2 from methanol is the decomposition of pure methanol.The decomposition reaction is endothermic with a 90.7 kJ/mol heat of reaction. Therefore, heat must be provided to maintain the reaction. Apart from being harmful to health, carbon monoxide produced is an atmospheric pollutant and a poison for the fuel cell [6]. So, some downstream processing must be done to eliminate the CO from the system before releasing the product stream to the fuel cell. The decomposition can also produce undesired by products such as di-methyl-ether and methane.
In this communication, we present the effect of catalyst formulation and also the reaction conditions on the production of hydrogen from methanol through decomposition over Pt and Pd catalysts.
Section snippets
Sol–gel method
To prepare Pt/Al2O3 and Pd/Al2O3 in a single step with the sol–gel method, a known amount of aluminum isopropoxide (AIP), 98% (from Alfa Aesar Inc.) was hydrolyzed in water at 85 °C and then a small amount of nitric acid was added to obtain a clear sol [7]. After that, the necessary amount of either H2PtCl6 or Pd(NO3)2 precursor was added to obtain the desired metal loading (from 1 to 10 wt%) in the final catalyst formulation. Ceria doped catalysts were also prepared in the same way as the
Effect of Pt loading
In this set of experiments, we explored the effect of changing the platinum loading on decomposition activity of methanol and the composition of the product stream. One of the goals was to find the optimal amount of platinum to be incorporated into the pure alumina support. Three loadings of platinum were investigated; 2%, 5% and 9%. Pure methanol diluted with helium gas was decomposed by these catalysts. The results of the activity tests for different Pt loading catalysts on sol–gel alumina
Conclusions
Our results show that Pt/ceria–alumina catalysts are very selective and active methanol decomposition catalysts. The activity increases with Pt loading. Ceria promoted catalysts are significantly more active than unpromoted catalysts. We find that the optimum ceria loading is in the neighborhood of 10%. Promotion with zirconia results in lower activity. The performance of Pd catalysts was found to be comparable to Pt catalysts of the same wt% metal loading. The 9% Pt–10% CeO2/Al2O3 catalyst
Acknowledgements
We gratefully acknowledge financial support of this research by the National Science Foundation and the Department of Education and Department of Energy.
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