WO 3 -based catalysts supported on porous clay heterostructures (PCH) with Si–Zr pillars for synthetic esters production

Abstract In this study, a porous clay with tunable pores was used as catalytic support, with the purpose of enhancing the accessibility of dispersed WO3 inside the pores and minimizing the mass transfer limitations of bulky fatty acids and larger alcohols in the catalyst. WO3-based catalysts supported on porous clay heterostructures (PCH) with Si–Zr pillars prepared by incipient wetness impregnation were evaluated for the esterification reaction of ricinoleic acid (FACO) with 2-ethylhexanol (2-EH). Various catalysts with different Si/Zr molar ratios (Si/Zr = 1, 2, 5, 10 and 15) and different WO3 loadings (5, 10, 20 and 30 wt.%) were prepared and the influence of their properties on the catalytic performance was studied. The catalysts were characterized by XRD, nitrogen adsorption–desorption isotherms at − 196 °C, NH3-TPD, XPS, Raman and UV–vis spectroscopies. The leaching of the catalysts was determined by ICP-MS. The highest values of reaction conversion were achieved by using the PCH with a Si/Zr molar ratio of 15 and 20 wt.% of WO3, denoted as Zr15–20WO3. The best reaction conditions were a temperature of 120 °C using 10 wt.% catalyst with a 2-EH-to-FACO molar ratio of 2:1, being the observed values of conversion equal to 71 and 91% after 8 and 24 h, respectively. The catalysts did not show leaching of zirconium and tungsten species in the reaction medium which demonstrated the high stability of these catalysts.