The effect of support on RhFe/Al2O3 for ethanol synthesis via CO hydrogenation

Different alumina samples prepared with sol–gel, chemical precipitation and hydrothermal synthesis were used as supports of Fe-promoted Rh-based catalysts for ethanol synthesis via CO hydrogenation. The samples were characterized by means of N2-adsorpotion, XRD, H2-TPR, XPS, STEM, H2-TPD, DRIFTS, H2 and CO chemisorption. The results indicated that the Al2O3 prepared by hydrothermal synthesis exhibited nano-fiber morphology and constituted of mixed crystal phases, while Al2O3 prepared by sol–gel and chemical precipitation shows no changes of morphology and crystal phases compared with the commercial Al2O3. In addition, nano-fiber Al2O3-supported Rh-based catalyst shows higher ethanol selectivity, which is ascribed to the lower metal–support interaction, higher dispersion and stronger CO insertion ability.

Ethanologenesis and respiration in a pyruvate decarboxylase-deficient Zymomonas mobilis

Objective Zymomonas mobilis is an alpha-proteobacterium with a rapid ethanologenic pathway, involving Entner–Doudoroff (E–D) glycolysis, pyruvate decarboxylase (Pdc) and two alcohol dehydrogenase (ADH) isoenzymes. Pyruvate is the end-product of the E–D pathway and the substrate for Pdc. Construction and study of Pdc-deficient strains is of key importance for Z. mobilis metabolic engineering, because the pyruvate node represents the central branching point, most novel pathways divert from ethanol synthesis. In the present work, we examined the aerobic metabolism of a strain with partly inactivated Pdc. Results Relative to its parent strain the mutant produced more pyruvate. Yet, it also yielded more acetaldehyde, the product of the Pdc reaction and the substrate for ADH, although the bulk ADH activity was similar in both strains, while the Pdc activity in the mutant was reduced by half. Simulations with the kinetic model of Z. mobilis E-D pathway indicated that, for the observed acetaldehyde to ethanol production ratio in the mutant, the ratio between its respiratory NADH oxidase and ADH activities should be significantly higher, than the measured values. Implications of this finding for the directionality of the ADH isoenzyme operation in vivo and interactions between ADH and Pdc are discussed.