Title

Development of nickel-based catalysts for hydrogen production from methane and methanol

Date of Completion

January 2005

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

Thermal decomposition of nickel acetate (T>300°C) dispersed on either silica or cordierite supports results in a mixture of Nio/NiO that was catalytically active for the decomposition of methane to produce CO-free hydrogen---without requiring any pretreatment (i.e. using H2 at high temperature (>500°C) during at least 2 hours). The carbon yield (gC/gNi), for the catalysts supported on SiO2 (ca. ∼200--300 m2g-1), increased with an increase in the catalyst NiO mean crystallite size. XRD and FE-SEM studies confirmed the formation of graphitic-type carbon filaments during the methane decomposition. ^ This dissertation has also been undertaken to investigate the effect of nickel precursor on the activity and selectivity of MnO-promoted Ni/SiO 2 catalyst for methanol decomposition. Particularly, the differences between nickel nitrate and nickel acetate as nickel precursor were examined. Manganese was used as a promoter due to its proven capacity for decrease CO hydrogenation over nickel. Contrary to nickel nitrate, nickel acetate is an excellent precursor to prepare catalysts with small nickel particles (<5 nm) and high surface area supported over SiO2, via calcination. However, these catalysts with small Nio particles (∼4 nm) favored CO methanation during methanol decomposition at high temperature (e.g. 350°C). ^ Under oxidative conditions, the partial oxidation of methanol occurred simultaneously with methanol decomposition, increasing the H2 yield. This reaction was favored over the catalyst with bigger Nio particles size (∼12 nm). Direct reduction of the catalysts prepared with nickel acetate in the presence of manganese, caused sintering of the nickel particles. ^ The kinetics of birnessite crystallization via the oxidation of Mn 2+ with O2 has been studied. To study the kinetics of this reaction was necessary to overcome O2 mass transfer limitations. The synthesis of pure birnessite was accomplished in excess O2, using an optimized oxidation process. The effect of three experimental parameters on the Mn2+ oxidation was considered: (1) oxygen flow rate, (2) reaction temperature, and (3) metal doping with Co 2+, Fe3+, and Ni2+. The reaction was described using a pseudo-first-order rate law model. Crystallization rates and the activation energy for the oxidation method were determined. ^