Multifunctional halloysite and hectorite catalysts for effective transformation of biomass to biodiesel

Halloysite surface was modified with tetrabutylammonium iodide, and then the obtained nanomaterial was usedas support for ZnO nanoparticles. After characterization, the nanomaterial was used as a catalyst for fatty acidmethyl esters (FAMEs) production. The recyclability of the nanomaterial was also investigated, and the optimizationof reaction conditions by the design of experiments approach was performed as well. In addition, thesynthesized nanomaterial was tested as a catalyst for FAME production from a series of waste lipids affordingbiodiesel in moderate to good yields (35–95%), depending on the matrix. To fully exploit the feasibility of clayminerals as catalysts in biodiesel formation, a screening of different clays and clay minerals with differentmorphologies and compositions, such as sepiolite, palygorskite, bentonite, and hectorite was also performed inthe esterification of FFAs (a mixture of 1:1 palmitic and stearic acids). Finally, hectorite, chosen as a model of 2:1clay minerals, was covalently modified, and tested as a catalyst in the esterification of FFAs.