**Microwave-Assisted Aldol Condensation of Furfural and Acetone over Mg–Al Hydrotalcite-Based Catalysts**

#### **Alberto Tampieri, Matea Lilic, Magda Constantí and Francesc Medina \***

DEQ, ETSEQ, Universitat Rovira i Virgili, Avinguda dels Països Catalans 26, 43007 Tarragona, Spain; alberto.tampieri@urv.cat (A.T.); lilicmatea@gmail.com (M.L.); magdalena.constanti@urv.cat (M.C.)

**\*** Correspondence: francesc.medina@urv.cat

Received: 4 August 2020; Accepted: 16 September 2020; Published: 18 September 2020

**Abstract:** The depletion of fossil fuel resources has prompted the scientific community to find renewable alternatives for the production of energy and chemicals. The products of the aldol condensation between bio-based furfural and acetone have been individuated as promising intermediates for the preparation of biofuels and polymeric materials. We developed a protocol for the microwave-assisted condensation of these two compounds over hydrotalcite-based materials. Mg:Al 2:1 hydrotalcite was prepared by co-precipitation; the obtained solid was calcined to afford the corresponding mixed metal oxide, which was then rehydrated to obtain a meixnerite-type material. The prepared solids were characterized by PXRD, ICP-AES, TGA-DSC and N2 physisorption, and tested as catalysts in the aldol condensation of acetone and furfural in a microwave reactor. The performance of the catalysts was assessed and compared; the meixnerite catalyst proved to be the most active, followed by the mixed metal oxide and the as-synthesized hydrotalcite, which has often been reported to be inactive. In all cases, the reaction is quite fast and selective, which makes our protocol useful for rapidly converting furfural and acetone into their condensation products.

**Keywords:** microwave-assisted organic synthesis; biofuel production; rehydrated hydrotalcite; layered double hydroxide; heterogeneous basic catalysis; green chemistry
