Production of hydrogen from the low-temperature steam reforming of methanol
Idem, Raphael Oyom
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The purpose of this work was to design and develop a high performance catalyst for the production of hydrogen from the low-temperature steam reforming of methanol and, also, to develop the kinetics of the methanol-steam reforming process. Catalyst design and development utilized a five-phase program involving the identification and subsequent optimization of the catalyst characteristics responsible for high catalytic performance. Extensive catalyst characterization and performance evaluation were carried out in each phase to provide the tools required for optimization. The base for this program was the highly active coprecipitated Cu-Al catalyst. Subsequent phases involved improvement of this Cu-Al catalyst by optimizing copper concentration and calcination temperature, type and concentration of promoter, and catalyst activation technique. In each phase, methanol decomposition and steam reforming reactions were performed in a microreactor at atmospheric pressure over reaction temperatures ranging from 170-250° and methanol space velocities (WHSV) of 26.4 and 16.7 h -1, respectively. Hydrogen production was a strong function of catalyst reducibility, copper concentration, type and concentration of promoter, reaction temperature, and type of feed. Also, hydrogen production efficiency depended strongly on the Cu1/Cu0 wt ratio in the activated catalyst. Maximum methanol conversions of 93 and 99 mol % and H2 selectivities of 99 and 93 mol % were obtained from the Mn-promoted and vaporized methanol-steam activated catalyst at 200 and 250°C, respectively. Favorable catalyst characteristics were such that the promoter, calcination temperature and the activation process not only conditioned the catalyst to produce optimum amounts of active Cu0, Cu1 and Bronsted base sites but also ensured that these sites were maintained during the reaction. The performance of the catalyst developed (p-5CM2) was superior to those reported in the literature for both high and low reaction temperatures. Results from kinetic studies showed for the first time that the rate controlling mechanism for the methanol-steam reforming process depended strongly on the Cu0 - Cu2O redox ability of the catalyst which, in turn, was a strong function of activation and reaction temperatures. The rate controlling steps for the methanol-steam reforming process at low and high reaction temperatures were found to be methanol dissociation and methyl formate hydrolysis, respectively.