Metal chlorides grafted on SAPO-5 (MCl_x/SAPO-5) as reusable and superior catalysts for acylation of 2-methylfuran under non-microwave instant heating condition

Highly active metal chlorides grafted on silicoaluminophosphate number 5, MCl_x/SAPO-5 (M = Cu, Co, Sn, Fe and Zn) catalysts via simple grafting of respective metal chlorides (MCl_x) onto SAPO-5 are reported. The study shows that thermochemical treatment after grafting is essential to ensure the formation of chemical bondings between MCl_x and SAPO-5. In addition, the microscopy, XRD and nitrogen adsorption analyses reveal the homogeneous distribution of MCl_x species on the SAPO-5 surface. Furthermore, the elemental microanalysis confirms the formation of Si-O-M covalent bonds in ZnCl_x/SAPO-5, SnCl_x/SAPO-5 and FeCl_x/SAPO-5 whereas only dative bondings are formed in CoCl_x/SAPO-5 and CuCl_x/SAPO-5. The acidity of MCl_x/SAPO-5 is also affected by the type of metal chloride grafted. Thus, their catalytic behavior is evaluated in the acid-catalyzed acylation of 2-methylfuran under novel non-microwave instant heating conditions (90-110°C, 0-20 min). ZnCl_x/SAPO-5, which has the largest amount of acidity (mainly Lewis acid sites), exhibits the best catalytic performance (94.5% conversion, 100% selective to 2-acetyl-5-methylfuran) among the MCl_x/SAPO-5 solids. Furthermore, the MCl_x/SAPO-5 solids, particularly SnCl_x/SAPO-5, FeCl_x/SAPO-5 and ZnCl_x/SAPO-5, also show more superior catalytic performance than common homogeneous acid catalysts (H₂SO₄, HNO₃, CH₃COOH, FeCl₃, ZnCl₂) with higher reactant conversion and catalyst reusability, thus offering a promising alternative for the replacement of hazardous homogeneous catalysts in Friedel-Crafts reactions.