Journal
ACS CATALYSIS
Volume 7, Issue 7, Pages 4550-4563Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.7b01381
Keywords
rhodium; iron; manganese; synthesis gas; ethanol; oxygenates
Categories
Funding
- Research Innovation Committee of the College of Engineering at the University of Wisconsin
- National Science Foundation through University of Wisconsin Materials Research Science and Engineering Center [DMR-1121288]
- Wisconsin Materials Research Science and Engineering Center [DMR-1121288]
- Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) [DE-EE0006878]
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-SC0014058]
- Sao Paulo Research Foundation-FAPESP (BEPE) [2015/20477-1]
- FAPESP [2015/23900-2]
- National Counsel of Technological and Scientific Development-CNPq [309373/2014-0]
- U.S. Department of Energy, Basic Energy Sciences (DOE-BES), Division of Chemical Sciences [DE-FG02-05ER15731]
- Department of Energy's Office of Biological and Environmental Research located at PNNL
- US Department of Energy, Office of Science [DE-AC02-06CH11357, DE-AC02-05CH11231]
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [15/20477-1] Funding Source: FAPESP
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Rh/SiO2 catalysts promoted with Fe and Mn are selective for synthesis gas conversion to oxygenates and light hydrocarbons at 523 K and 580 psi. Selective anchoring of Fe and Mn species on Rh nanoparticles was achieved by controlled surface reactions and was evidenced by ultraviolet visible absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The interaction between Rh and Fe promotes the selective production of ethanol through hydrogenation of acetaldehyde and enhances the selectivity toward C-2 oxygenates, which include ethanol and acetaldehyde. The interaction between Rh and Mn increases the overall reaction rate and the selectivity toward C2+ hydrocarbons. The combination of Fe and Mn on Rh/SiO2 results in trimetallic Rh-Fe-Mn catalysts that surpass the performance of their bimetallic counterparts. The highest selectivities toward ethanol (36.9%) and C-2 oxygenates (39.6%) were achieved over the Rh-Fe-Mn ternary system with a molar ratio of 1:0.15:0.10, as opposed to the selectivities obtained over Rh/SiO2, which were 3.5% and 20.4%, respectively. The production of value-added oxygenates and C2+ hydrocarbons over this trimetallic catalyst accounted for 55% of the total products. X-ray photoelectron spectroscopy measurements suggest that significant fractions of the Fe and Mn species exist as metallic iron and manganese oxides on the Rh surface upon reduction. These findings are rationalized by density functional theory (DFT) calculations, which reveal that the exact state of metals on the surfaces is condition-dependent, with Mn present as Mn(I) and Mn(II) oxide on the Rh (211) step edges and Fe present as Fe(I) oxide on the step edge and metallic subsurface iron on both Rh steps and terraces. CO Fourier transform infrared spectroscopy and DFT calculations suggest that the binding of CO to Rh (211) step edges modified by Fe and/or manganese oxide is altered in comparison to CO adsorption on a clean Rh (211) surface. These results suggest that Mn2Ox species and Fe and Fe2O modify bonding at Rh step edges and shift reaction selectivity away from CH4.
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