The Effects of PdZn Crystallite Size on Methanol Steam Reforming

Exceptional activity and selectivity of Pd/ZnO catalysts for methanol steam reforming have been attributed to the formation of PdZn alloy. In this paper, we evaluated the crystallite size effects of PdZn alloy on methanol steam reforming. An organic preparation method was used to avoid the complexity from the alteration of ZnO morphology typically associated with the conventional aqueous preparation method. Both Pd loading and reduction temperature (>350 °C) were used to vary the crystallite size of PdZn alloy. Experimental activity studies and transmission electron microscope (TEM) characterizations indicated that formation of large sized PdZn crystallites exhibit high reactivity and low CO selectivity during methanol steam reforming.     

Membrane reactors for hydrogen production

Fuel cell powered vehicles with on board reforming need compact and lightweight components. A membrane reactor, that combines hydrogen permeable membranes with a methanol steam reformer promises considerable weight and space savings. Its dense metal membranes produce high purity hydrogen over a wide range of pressure and load. The selective removal of hydrogen yields methanol- and CO-conversions that are higher than the equilibrium conversion in a conventional reactor. Results with three different metal membranes in a membrane reactor for steam reforming of methanol are presented. A mathematical model accurately describes the measured performance of the membrane reactor and allows predictions for other values of the process parameters.     

Selective steam reforming of methanol over silica-supported copper catalyst prepared by sol–gel method

Silica-supported copper prepared by a sol–gel method can selectively catalyze methanol steam reforming to hydrogen and carbon dioxide at 250 °C. The catalytic activity increases with the copper content up to 40 wt.%. The selectivity to carbon monoxide with the catalysts containing 20–40 wt.% of copper is significantly lower than that with a commercial Cu/ZnO/Al₂O₃ catalyst. Copper particles are highly dispersed in the catalyst whose Cu content is 20 wt.% or less. After the reaction at 250 °C the particles are present as Cu₂O with the mean crystallite size less than 4 nm. In the catalyst with the Cu content of 30–50 wt.%, the fine Cu₂O particles coexist with large metallic Cu particles whose mean crystallite size is 30–40 nm after the reaction. The large metallic particles are supposed to contribute to the reaction as well as the fine Cu₂O particles although the surface area is estimated to be significantly smaller than that of the latter.     

Co/CeO2-ZrO2 catalysts prepared by impregnation and coprecipitation for ethanol steam reforming

Co/CeO₂-ZrO₂ catalysts for the ethanol steam reforming were prepared by wet incipient impregnation and coprecipitation methods. These catalysts were characterized by nitrogen adsorption, TEM-EDX, XRD, H₂-TPR, and CO chemisorption techniques. It was found that the catalyst reducibility was influenced by the preparation methods; catalysts with different reduction behaviors in the pre-reduction showed different catalytic activities toward hydrogen production. The H₂-TPR studies suggested the presence of metal–support interactions in Co/CeO₂-ZrO₂ catalysts during their hydrogen pre-reduction, a necessary treatment process for catalysts activation. These interactions were influenced by the preparation methods, and the impregnation method is a favorable method to induce a proper metal–support effect that allows only partial reduction of the cobalt species and leads to a superior catalytic activity for the hydrogen production through ethanol steam reforming. At 450 °C, the impregnated catalyst gives a hydrogen production rate of 147.3 mmol/g-s at a WHSV of 6.3 h⁻¹ (ethanol) and a steam-to-carbon ratio of 6.5.