The spent catalyst after use under the optimal set of conditions (Section 3.3) was then washed with solvents (see Section 2.7) and then reused under the same optimal conditions. The FAME yield obtained with successive reuse of the catalyst is shown in Fig. 8, where the FAME yield obtained after two, three and four uses of the catalyst was 1.03-, 1.08- and 1.09-fold lower than that for the unused catalyst. Thus, the SO3H-MCM-41 catalyst has a relatively high stability and may potentially be reusable. The spent catalyst after four reuse was presented the weak Cdouble bond; length as m-dashO spectra at wave number 1738 cm−1 from carbonyl containing compounds (Fig. 2) which was attracted by sulfonic group to reduce the catalytic activity of spent catalyst