Hydrogen from methanol steam-reforming over Cu-based catalysts with and without Pd promotion

The catalytic steam reforming of methanol has been investigated over Cu-based catalysts with and without Pd addition, and comparing with typical commercial catalysts. The most active commercial catalyst had an activity comparable to values reported in the literature. The effect of adding Pd to a CuZn catalyst was twofold. The initial start-up properties of the catalyst were improved, allowing a rapid attainment of the activity without any pre-reduction of the catalyst. However, the addition of Pd also led to poorer selectivity, due to a significant increase in the selectivity to CO.     

Efficient surrogate models for reliability analysis of systems with multiple failure modes

Despite many advances in the field of computational reliability analysis, the efficient estimation of the reliability of a system with multiple failure modes remains a persistent challenge. Various sampling and analytical methods are available, but they typically require accepting a tradeoff between accuracy and computational efficiency. In this work, a surrogate-based approach is presented that simultaneously addresses the issues of accuracy, efficiency, and unimportant failure modes. The method is based on the creation of Gaussian process surrogate models that are required to be locally accurate only in the regions of the component limit states that contribute to system failure. This approach to constructing surrogate models is demonstrated to be both an efficient and accurate method for system-level reliability analysis.     

Steam Reforming of Ethanol Over Supported Co and Ni Catalysts

The ethanol steam reforming has been investigated over supported cobalt catalysts at atmospheric pressure. About 12% cobalt was supported on Al₂O₃, SiO₂ and TiO₂, and a commercial Ni/Al₂O₃ catalyst (G90B) was included for comparative purposes. The selectivity was found to depend strongly on the support, especially at low and medium temperatures. The initial activity of the cobalt catalysts correlated well with the metal dispersion. Acetaldehyde was an important C-containing product at low temperatures, whereas at high temperatures CO, CO₂ and CH₄ dominated the product spectrum. A significant production of ethene was observed, especially on the alumina-supported catalysts. The results are in agreement with a mechanism involving acetaldehyde as an intermediate in the steam reforming. At high temperatures (>550 °C) the conversion was complete and the product distribution approaches the equilibrium. The H₂ yield approached 5 moles H₂/mole ethanol converted, which is close to the maximum according to thermodynamic calculations. The alumina-supported catalysts (both Co and Ni) showed acceptable deactivation rates, but high carbon formation.     

Transformation of propane,n-butane and n-hexane over H3PW12O40 and cesium salts. Comparison to sulfated zirconia and mordenite catalysts

Over H₃PW₁₂O₄₀ and its acidic cesium salts at 250°C, alkane transformations occur through the mechanisms previously proposed for sulfated zirconia and mordenite catalysts: propane is mainly transformed into butanes through a trimerization–isomerization–cracking process, n-butane into isobutane, propane and pentanes through a dimerization–isomerization–cracking process, n-hexane into methylpentanes and 2,3-dimethylbutane through a monomolecular mechanism. With all the samples, n-butane transformation is initially much faster than propane transformation, the difference in rate increasing significantly with the Cs content: from 25 times with H₃PW₁₂O₄₀ to 350 times with Cs_2.4H_0.6PW₁₂O₄₀. On the other hand, n-hexane transformation is 2.3 to 7 times faster than n-butane transformation. A decrease in acid strength and in acid site density with Cs introduction is proposed to explain the increase in the rate ratios. For all the reactions, sulfated zirconia pretreated at 600°C is 2–3 times more active than the heteropolycompounds. HMOR10 which is the most active catalyst for n-hexane transformation is the least active for n-butane and especially propane transformation. This very low activity of mordenite for these bimolecular processes can be related to particularities of its pore system: bimolecular reactions are strongly unfavoured in the narrow non-interconnected channels of this zeolite. This revised version was published online in August 2006 with corrections to the Cover Date.