  Citation: Sagar,T.V.; Zavašnik, J.; Finšgar, M.; Novak Tušar, N.; Pintar, A. Evaluation of Au/ZrO 2 Catalysts Prepared via Postsynthesis Methods in CO 2 Hydrogenation to Methanol. Catalysts 2022, 12, 218. https:// doi.org/10.3390/catal12020218 Academic Editors: Vincenzo Vaiano and Olga Sacco Received: 26 January 2022 Accepted: 11 February 2022 Published: 14 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Article Evaluation of Au/ZrO 2 Catalysts Prepared via Postsynthesis Methods in CO 2 Hydrogenation to Methanol Tatiparthi Vikram Sagar 1 , Janez Zavašnik 2 , Matjaž Finšgar 3 , Nataša Novak Tušar 1 and Albin Pintar 1, * 1 Laboratory for Environmental Sciences and Engineering, Department of Inorganic Chemistry and Technology, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia; tvikramsagar@gmail.com (T.V.S.); natasa.novak.tusar@ki.si (N.N.T.) 2 Department of Gaseous Electronics, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; janez.zavasnik@ijs.si 3 Faculty of Chemistry and Chemical Engineering, University of Maribor, SI-2000 Maribor, Slovenia; matjaz.finsgar@um.si * Correspondence: albin.pintar@ki.si; Tel.: +386-1476-0237; Fax: +386-1476-0460 Abstract: Au nanoparticles supported on ZrO 2 enhance its surface acidic/basic properties to produce a high yield of methanol via the hydrogenation of CO 2 . Amorphous ZrO 2 -supported 0.5–1 wt.% Au catalysts were synthesized by two methods, namely deposition precipitation (DP) and impregnation (IMP), characterized by a variety of techniques, and evaluated in the process of CO 2 hydrogenation to methanol. The DP-method catalysts were highly advantageous over the IMP-method catalyst. The DP method delivered samples with a large surface area, along with the control of the Au particle size. The strength and number of acidic and basic sites was enhanced on the catalyst surface. These surface changes attributed to the DP method greatly improved the catalytic activity when compared to the IMP method. The variations in the surface sites due to different preparation methods exhibited a huge impact on the formation of important intermediates (formate, dioxymethylene and methoxy) and their rapid hydrogenation to methanol via the formate route, as revealed by means of in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analysis. Finally, the rate of formation of methanol was enhanced by the increased synergy between the metal and the support. Keywords: Au/ZrO 2 ; CO 2 hydrogenation; methanol synthesis; in situ DRIFTS; CO 2 utilization 1. Introduction The production of carbon-based pollutants through the utilization of fossil fuels has increased enormously since the industrial revolution. Strategies to reduce CO 2 emissions in the atmosphere are essential [1–4]. In this regard, CO 2 is considered to be an abundant C1 source [5] that can be used as a raw material to produce vital value-added products, such as syngas, dimethyl ether, formic acid, methane, higher hydrocarbons, and methanol, etc. [6–8]. Among all of the CO 2 conversion routes, most studies in recent years have been focused on CO 2 hydrogenation to methanol [9]. Methanol has several important applications, including usage in the plastic industry and as a solvent in many important organic reactions [1,10]. The main use of methanol is as a primary feedstock for the produc- tion of different commodity chemicals [11]. Currently, industrial methanol production is carried out using synthesis gas (CO/CO 2 /H 2 ) with Cu/ZnO/Al 2 O 3 -based catalysts at high pressure (50−100 bar) [8,12–14]. The CO and CO 2 hydrogenation reactions require high pressure to ensure the maximum conversion and high selectivity towards methanol; hence, the research focuses on the development of efficient catalysts for direct CO 2 hydrogenation to methanol. The important reactions of methanol production are as follows: CO 2 + 3H 2 → CH 3 OH + H 2 O → ΔH ◦ = −49.5 kJ mol −1 (1) CO 2 +H 2 → CO + H 2 O → ΔH ◦ = +41.2 kJ mol −1 (2) Catalysts 2022, 12, 218. https://doi.org/10.3390/catal12020218 https://www.mdpi.com/journal/catalysts