Insights into CO2 Hydrogenation: Tuning the Selectivity towards Alcohols by Investigating Ni-Fe Bimetallic Catalysts
Analytical Chemistry
Final Report Abstract
Conversion of CO2 as greenhouse gas into value-added products, e.g., chemicals and fuels, constitutes a promising starting point to tackle the challenge of rising atmospheric CO 2 concentration and associated proceeding climate change. In this context, thermo-catalytic hydrogenation of CO2 over non-noble, abundant, relatively inexpensive metals can constitute a major advance. For CO2 conversion into methane, Ni-based catalysts are desired due to their high activity and selectivity. However, for taking a step towards other value-added products, the optimal catalyst is not yet found. Synergistically combining two metals is an important strategy to tune the selectivity and activity of a catalytic reaction, by taking advantage of the selectivity of one metal and the activity of the second metal in a combined fashion. For bimetallic catalysts, improved performance is frequently ascribed to metal alloy formation, although it is not yet well-understood how the two metals interact and boost the catalytic performance. Moreover, the concept of synergistically combining two metals can likewise be transferred to a trimetallic system. Accordingly, adding Fe or/and Cu to the well-investigated Ni/SiO2 system constitutes a promising approach for tuning the selectivity in CO2 hydrogenation. However, with increasing complexity of the catalytic system, the application of suitable operando characterization techniques becomes even more important to gain insights into structure-composition-performance correlations. In this project, an optimized synthesis was used to support small (< 2 nm), highly dispersed nanoparticles on SiO2. A multifaceted operando characterization approach was applied to gain insights into the bi- and trimetallic Ni-Fe, Ni-Cu, and Ni-Cu-Fe systems and corresponding monometallic counterparts. In the first part of the project, a setup for operando laboratory-based X-ray absorption spectroscopy (XAS) was successfully developed and both metal- and metal ratio-dependent differences in the reducibility and catalytic performance of the multi-metal catalysts were revealed. The synergistic effects between the metals unambiguously tune the selectivity in CO2 hydrogenation from methane to CO, being an important intermediate for the formation of C2+ products. The new possibility to perform operando XAS in the laboratory expands the potential field of applications towards a broad research community. In the second part of the project, combining operando infrared spectroscopy, (quick-)XAS, and high-pressure X-ray photoelectron spectroscopy constituted a powerful tool to unravel synergistic effects in multi-metal CO2 hydrogenation catalysts being particularly important for a more rational design of next generation catalysts. Besides particle size, reducibility, degree of reduction as well as reoxidation, surface chemistry and C-species, dynamic behavior, and catalytic performance were revealed to be metal- and metal ratio-dependent.
Publications
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A Collaboration for Guiding the Rational Design of Multielement Solid Catalysts. Angewandte Chemie International Edition, 62(7).
N.S., Genz et al.
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Operando Laboratory‐Based Multi‐Edge X‐Ray Absorption Near‐Edge Spectroscopy of Solid Catalysts. Angewandte Chemie International Edition, 61(48).
Genz, Nina S.; Kallio, Antti‐Jussi; Oord, Ramon; Krumeich, Frank; Pokle, Anuj; Prytz, Øystein; Olsbye, Unni; Meirer, Florian; Huotari, Simo & Weckhuysen, Bert M.
