Speaker
Description
Against the background of dwindling fossil fuel resources and the threats of climate change, sustainable and environmentally friendly production processes for fuels and chemical feedstock become all the more important. Methanol, a liquid fuel of high energy density, may pave the way to sustainable society [1]. It can be produced from green H$_2$ generated via electrochemical water-splitting using solar or wind power, and the greenhouse gas CO$_2$, extracted from air or already available concentrated at industrial sites [1]. In today’s catalytic industry the synthesis of methanol is carried out from a mixture of H$_2$, CO and CO$_2$ over Cu/ZnO/Al$_2$O$_3$ catalysts, where high gas pressures (50-100 bar) are required [2]. This traditional high pressure methanol synthesis does not only bring along safety risks and a high energy consumption, but restricts the CO$_2$ concentration to a maximum of about 10% of the gas feed, since greater amounts result in a reduced methanol selectivity [6]. Accordingly, safe and energy-saving low pressure pathways for the methanol production using a higher percentage of CO$_2$ feeds are highly desirable.
Recently, intermetallic compounds, including NiGa alloys, have attracted much attention as novel catalyst materials of improved stability, selectivity and activity for CO2 hydrogenation into methanol already at ambient pressures [3-6]. However, the underlying reaction mechanisms for CO2 hydrogenation and the nature of the active species in the NiGa system are still unclear. Accordingly, in-situ and operando studies on well-defined NiGa nanocatalysts are required.
In this work, we use a multi-probe approach combining operando X-ray absorption spectroscopy, operando powder X-ray diffraction and near-ambient pressure X-ray photoelectron spectroscopy with reactivity studies and ex situ microscopy techniques to shed light on the phase transitions and chemical compositions of SiO$_2$-supported micelle-based Ni$_5$Ga$_3$ and Ni$_3$Ga$_1$ nanoparticles under activation (in H$_2$) and reaction conditions for methanol synthesis (in CO$_2$ and H$_2$ mixture). This allows a direct correlation of the catalytic performance with the changes in structure, chemical state and surface composition of the catalysts, which will pave the way for an atomic-scale understanding of the hydrogenation of CO$_2$ into methanol at ambient pressure.
References:
[1] S. Kattel, P. J. Ramirez, J. G. Chen, J. A. Rodriguez, P. Liu, Science 355, 1296 (2017).
[2] M. Bukhtiyarova, T. Lunkenbein, K. Kähler, R. Schlögl, Catal. Letters 147, 416 (2017).
[3] M. Armbrüster, Science and Technology of Advanced Materials 21, 303 (2020).
[4] F. Studt, I. Sharafutdinov, F. Abild-Pedersen, C. F. Alkjaer, J. S. Hummelshoj, S. Dahl, I. Chorkendorff, J. K. Norskov, Nature Chem. 6, 320 (2014).
[5] I. Sharafutdinov, C. F. Elkjaer, H. W. P. de Carvalho, D. Gardini, G. L. Chiarello, C. D. Damsgaard, J. B. Wagner, J.-D. Grunwaldt, S. Dahl, I. Chorkendorff, J. Catal. 320, 77 (2014).
[6] J. Zhong, X. Yang, Z. Wu, B. Liang, Y. Huang, T. Zhang, Chem. Soc. Rev. 49, 1385 (2020).
