Construction of a Brönsted-Lewis solid acid catalyst La-PW-SiO2/SWCNTs based on electron withdrawing effect of La(III) on π bond of SWCNTs for biodiesel synthesis from esterification of oleic acid and methanol

A novel solid Brönsted-Lewis acid catalyst La-PW-SiO₂/SWCNTs (single-wall carbon nanotubes) was synthesized from the synergistic modification of H₃PW₁₂O₄₀ (HPW) by single-walled carbon nanotubes functionalized with sidewall hydroxyl groups (SWCNTs–OH) and La³⁺ via sol–gel method. The freshly prepared catalyst was characterized by several methods, and the catalytic activity and stability of it were studied from the esterification of oleic acid and methanol. Results showed that the highest conversion of oleic acid was 93.1% (mass) and maintained as high as 88.7% (mass) after six cycles of La-PW-SiO₂/SWCNTs. The high catalytic activity and stability of La-PW-SiO₂/SWCNTs can be attributed to the strong electron withdrawing effect of La³⁺ on π bond of SWCNTs, because it can facilitate the formation of a large number of strong Lewis acid sites. Therefore, the reduction of catalytic activity of a solid acid catalyst due to the fact that hydration reaction of its Brönsted acid sites can be effectively reduced. La-PW-SiO₂/SWCNTs can be an efficient and economical catalyst, because it shows good catalytic activity and stability.