  Citation: Mabate, T.P.; Meijboom, R.; Bingwa, N. The Inorganic Perovskite-Catalyzed Transfer Hydrogenation of Cinnamaldehyde Using Glycerol as a Hydrogen Donor. Catalysts 2022, 12, 241. https://doi. org/10.3390/catal12020241 Academic Editors: Charles Xu and Tianliang Lu Received: 23 January 2022 Accepted: 10 February 2022 Published: 21 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 The Inorganic Perovskite-Catalyzed Transfer Hydrogenation of Cinnamaldehyde Using Glycerol as a Hydrogen Donor Tafadzwa Precious Mabate 1 , Reinout Meijboom 1,2 and Ndzondelelo Bingwa 1,2, * 1 Research Center for Synthesis and Catalysis, Department of Chemical Sciences, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa; 201516781@student.uj.ac.za (T.P.M.); rmeijboom@uj.ac.za (R.M.) 2 Centre for Nanomaterials Science Research, University of Johannesburg, Johannesburg 2092, South Africa * Correspondence: nbingwa@uj.ac.za; Tel.: +27-115-592-363; Fax: +27-115-592-819 Abstract: Catalytic transfer hydrogenation reactions (CTHs) produce value-added chemicals in the most economical, safe, green, and sustainable way. However, understanding the reaction mechanism and developing stable, selective, and cheap catalysts has been a significant challenge. Herein, we report on the hydrogenation of cinnamaldehyde utilizing glycerol as a hydrogen donor and metal- oxides (SnO 2 , LaFeO 3 , and LaSnO 3 ) as heterogeneous catalysts. The perovskite types were used because they are easy to synthesize, the metal components are readily available, and they are good alternatives to noble metals. The catalysts were synthesized through the nanocasting (hard-template) method with SiO 2 (KIT-6) as a template. The template was synthesized using the soft-template (sol-gel) method resulting in a high surface area of 624 m 2 /g. Furthermore, catalytic evaluations gave high cinnamaldehyde percentage conversions of up to 99%. Interestingly, these catalysts were also found to catalyze the etherification of glycerol in one pot. Therefore, we propose competitive surface catalytic reactions driven by the transition metal cations as the binding sites for the cinnamaldehyde and the sacrificial glycerol. Keywords: catalytic transfer hydrogenation; glycerol; etherification; perovskites 1. Introduction Sustainability is vital in different reactions as this provides the means to meet human needs using the efficiency of natural products for chemicals and services. Several reactions are performed to increase sustainability, such as converting biomass to fuels using renew- able chemicals [1–6]. The catalytic transfer hydrogenation reaction (CTH) also follows that direction as it uses renewable hydrogen donors such as bioderived sacrificial alcohols [7]. Moreover, this is a green approach that reduces greenhouse emissions and the pollution of the environment. The replacement of molecular H 2 with biomass-derived hydrogen donors also provides a safer alternative, as molecular hydrogen requires specialized handling and transportation and is deemed to be unsafe [8–10]. Furthermore, the same phase of the hydrogen donor and substrate increases the contact time, thus enhancing reaction efficiency due to the transport phenomena [11]. Previous reactions have used biomass-derived hydrogen donors for CTHs. Isopropanol and other monoprotic alcohols are the most used [12]. Among the mono- protic donors, isopropanol is a better hydrogen donor than n-propanol, ethanol, and methanol [10]. However, very few studies have been conducted using glycerol, a polypro- tic sacrificial alcohol [11,13,14]. Using glycerol instead of monoprotic donors could be a practical approach because it can also be used as a solvent. On compounds that have more than one reduction site in CTHs, selectivity for the desired product becomes a challenge. For example, in α,β-unsaturated combinations, two sites can be hydrogenated. These are the alkene double bond and the terminal carbonyl of the aldehyde moiety [15]. These two sites make it particularly challenging to synthesize Catalysts 2022, 12, 241. https://doi.org/10.3390/catal12020241 https://www.mdpi.com/journal/catalysts