*2.1. Catalyst Preparation*

Heteropolyacid catalysts were synthesized in duplicate according to Taguchi's L8 orthogonal array presented in Table 1, through which di fferent calcination temperatures (300 or 500 ◦C), 30% (*w*/*w*) active phases (H3PW12 O40—HPW or H3PMo12 O40—HPMo), and supports (Nb2O5 or Al2O3) were combined, resulting in 16 di fferent catalysts. The choice of the supports and active phases were made so that their combination resulted in catalysts with Lewis and Brønsted acid sites, which was derived from the support and active phase, respectively. The supports Nb2O5 (HY-340) and Al2O3 were supplied by Companhia Brasileira de Metalurgia e Mineração (CBMM) and Alcoa, respectively.

The catalysts were prepared according to the incipient wetness impregnation method which uses an amount of solvent which is lower than or equal to that required to fill in the support pores. For such a purpose, the active phase (HPW or HPMo) was dissolved in 70% ethanol solution at ambient temperature and mixed with the support (Nb2O5 or Al2O3) in three successive steps until reaching a final metal concentration of 30%. The catalytic solid was then dried at 100 ◦C for 2 h and subsequently calcined at 300 or 500 ◦C for 3 h, according to the conditions shown in Table 1. The assays were carried out in duplicate.
