Abstract
A series of bimetallic catalysts containing CoMo, RuMo, RhMo, CoW, RuW and RhW on γ-Al2O3 have appreciable activity for the reduction of carbon monoxide with hydrogen under mild conditions (150, 300°C and 101 to 407 kPa). Ru-W/γ-Al2O3 had the highest overall activity and propensity for chain growth, CoMo and CoW/γ-Al2O3 generated the highest yields of alkeneproducts, while RhMo and (methanol and ethanol). Alkali promotion of the RuW/γ-Al2O3 catalyst increased the alkene content of the products but decreased the overall activity for carbon monoxide hydrogenation. X-ray photoelectron spectroscopy indicated that both RuW and RuMo contain ruthenium with a slightly higher binding energy after reduction than the monometallic ruthenium catalyst. Molybdenum and tungsten are not reduced. X-ray photoelectron spectroscopy of the fresh RhMo/γ-Al2O3 catalyst indicates the presence of RhIII 2h, the rhodium is reduced, with a binding energy close to but slightly higher than that of bulk Rh0. Here too, the molybdenum binding energy is unaffected by reduction, and the rhodium-to-molybdenum atom ratio remains constant, suggesting little or no further sintering. High pressure (250°C, 1724-6689 kPa, hydrogen: carbon monoxide = 0.75:1.0) reduction of carbon monoxide with hydrogen by 3% Rh-2.8% Mo/γ-Al2O3 produced predominantly dimethyl ether and methane. This catalyst's activity and selectivity are quite stable over prolonged period (>300 h). Transmission electron microscopy of used RhMo/γ-Al2O3 shows that there is a bimodal distribution of particles (0.5 nm and 1.01.5 nm). Dedicated scanning transmission electron microscopy-energy dispersive spectroscopy of the particles indicates that the larger particles are enriched in rhodium (Rh-to-Mo>1.60) and the smaller in molybdenum (Rh-to-Mo<0.9). A structural model is proposed for Rh-Mo/γ-Al2O3 with two separate sites leading to oxygenates and hydrocarbons. Oxygenate production is attributed to chemistry at the smaller, molybdenum-rich site. It is believed that the role of molybdenum in this site is to act as a textural promoter, providing site-isolation of the rhodium.
Original language | English |
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Pages (from-to) | 351-375 |
Number of pages | 25 |
Journal | Applied Catalysis |
Volume | 61 |
Issue number | 1 |
DOIs | |
State | Published - 1990 |
Externally published | Yes |
Funding
Partial support for this research was provided by the Pittsburgh Energy and Technology Center of the Department of Energy.
Keywords
- STEM
- XPS)
- alkenes
- carbon monoxide hydrogenation.
- catalyst characterization (EDS
- cobalt-molybdenum
- cobalt-tungsten
- oxygenates
- rhodium-molybdenum
- rhodium-tungsten
- ruthenium-molybdenum
- ruthenium-tungsten
- syngas conversion
- γ-AlO