MPV Reduction of Furfural to Furfuryl Alcohol on Mg, Zr, Ti, Zr–Ti, and Mg–Ti Solids: Influence of Acid–Base Properties

Abstract

The Meerwein–Ponndorf–Verley (MPV) reaction is an environmentally-friendly process consisting of the reduction of a carbonyl compound through hydrogen transfer from a secondary alcohol. This work deals with MPV reduction of furfural to furfuryl alcohol on different ZrOx, MgOx, TiOx, and Mg–Ti, as well as Zr–Ti mixed systems. The solids were synthesized through the sol–gel process and subsequently calcined at 200 °C. Characterization was performed using a wide range of techniques: ICP-MS, N2 adsorption-desorption isotherms, EDX, TGA-DTA, XRD, XPS, TEM, TPD of pre-adsorbed pyridine (acidity) and CO2 (basicity), DRIFT of adsorbed pyridine, and methylbutynol (MBOH) test reaction. ZrOx showed the highest conversion and selectivity values, which was attributed to the existence of acid–base pair sites (as evidenced by the MBOH test reaction), whereas the introduction of titanium resulted in the drop of both conversion and selectivity probably due to the increase in Brönsted-type acidity. As for MgOx, it had a predominantly basic character that led to the production of the condensation product of one molecule of furfural and one molecule of acetone, and thus resulted in a lower selectivity to furfuryl alcohol. The TiOx solid was found to be mainly acidic and exhibited both Lewis and Brönsted acid sites. The presence of the latter could account for the lower selectivity to furfuryl alcohol. All in all, these results seemed to suggest that the MPV reaction is favored on Lewis acid sites and especially on acid–base pair sites. The process was accelerated under microwave irradiation.

An Account of the Catalytic Transfer Hydrogenation and Hydrogenolysis of Carbohydrate‐Derived Renewable Platform Chemicals over Non‐Precious Heterogeneous Metal Catalysts

“…For example, Urbano and coworkers employed various transition metal oxide catalysts, including ZrO x , MgO x , and TiO x , for the transfer hydrogenation of FUR at 100°C using 2-propoanol as H-donor solvent. [28] Among these catalysts, ZrO x afforded maximum FUR conversion (50 %) and the highest FOL selectivity (90 %). Characterization of these catalysts revealed that ZrO x possessed both Lewis acidic and Lewis basic sites, and the basic to acidic site ratio obtained from CO 2 TPD and pyridine TPD was 1.1.…”

“…Several research groups have employed transition metal oxide catalysts, and the activity of these catalysts has been attributed to both Lewis acid and Lewis basic sites, which facilitate the hydrogen transfer from the H‐donor molecule to FUR and result in FOL production. For example, Urbano and coworkers employed various transition metal oxide catalysts, including ZrO x , MgO x , and TiO x , for the transfer hydrogenation of FUR at 100 °C using 2‐propoanol as H‐donor solvent [28] . Among these catalysts, ZrO x afforded maximum FUR conversion (50 %) and the highest FOL selectivity (90 %).…”

“… Reaction mechanism of FUR conversion to FOL over ZrO x catalyst via MPV mechanism involving acid and basic sites [28] …”

“…Acidity and basicity determined by CO 2 and pyridine TPD and their influences in the transfer hydrogenation of FUR. [28] μmol CO 2 solvents. [29] The highest conversion of FUR was observed with 2propanol (54 %) followed by ethanol (53 %), 2-butanol (39 %), methanol (6 %), and tert-butanol (< 1%).…”

Microwave‐heated γ‐Alumina Applied to the Reduction of Aldehydes to Alcohols

“…A number of heterogeneous catalysts have been developed for the MPV reduction, [19] such as, zeolites, [20][21][22][23][24][25] mesoporous silicates, [26] hydrotalcite, [27,28] metal oxides [29][30][31][32][33][34][35] or metal-organic frameworks. [36,37] However, most of them involve complex synthetic routes with the incorporation of various metals [24,25,38,39] and in some cases rare metals.…”