Synthesis, characterization and catalysis of rhodium-molybdenum bimetallic catalysts and related metal-oxide catalysts for oxygenate synthesis.

摘要

New Rh-Mo catalysts were developed by using an organometallic Rh-Mo cluster as the catalyst precursor. Study of the cluster-derived catalysts in CO and CO{dollar}sb2{dollar} hydrogenation revealed a significant propensity for oxygenate formation on the catalysts, which was further confirmed by a kinetics study of the catalysts. In-situ infrared (IR) spectroscopic characterization of the catalysts uncovered that the rhodium active sites were highly isolated on the catalysts. The propensity to produce oxygenates by these catalysts was explained in terms of the enhanced site-isolation of rhodium by molybdenum.; The site-isolation effects were studied further on a series of alumina-supported rhodium and rhodium-molybdenum catalysts. Carbon monoxide hydrogenations on the catalysts reaffirmed the explicit role of the molybdenum promoter for enhancing the activity and oxygenate selectivity of the rhodium catalysts. Turn-over-frequency and stability data uncovered the distinctly different nature of the active sites of the rhodium and rhodium-molybdenum catalysts. In-situ IR, high resolution transmission electron microscopy and chemisorption studies of the catalysts provided strong evidence for the site-isolation effects of molybdenum.; Carbon monoxide hydrogenation study on a series of manganese oxides revealed the dependencies of selectivities and apparent activation energies for methanol formation on the initial O/Mn ratios of the oxides. The bulk structures of the used-oxides (=MnO) were, however, independent on initial O/Mn ratios of the oxides. These results were rationalized from the propensity of the defect-site formation on the oxides--a higher O/Mn ratio in the oxides may lead to a higher defect-site density upon removal of the lattice oxygen by reduction and reaction.; Further studies of oxygenate synthesis focused on mixed-oxide catalysts for isobutanol production. A series of Cu-Zn-Mn-Zr based catalysts were designed, prepared, tested, and characterized. Application of chemometrics to catalyst design and evaluation helped to identify the major effects of ZrO{dollar}sb2{dollar}/CuO and MnO/CuO ratios on the isobutanol selectivity. Various experimental factors, such as basic precipitants, alkali metal doping, transition metal promoter, calcination atmosphere, and reaction conditions were examined to improve the performance of the catalysts.