Bioethanol upgrading through condensation is of key interest in the development of sustainable processes, shifting from fossil to renewable carbon. Here, a new strategy is proposed, which combines in one catalyst an appropriate distribution of acid/basic sites of a mixed oxide with the presence of an active dehydrogenation phase (Cu nanoparticles). Experiments, performed in a fixed bed reactor, reveal a very positive effect of Cu in the performance of Mg−Al catalyst, with 1‐butanol productivity 12 times higher at 523 K under inert conditions. The improvement is even more notable in presence of H₂, almost 30 times higher, under same conditions. The presence of Cu on the surface increases the formation of acetaldehyde, limiting the extent of dehydration side‐reactions. In addition, hydrogen enhances the C4 hydrogenation, preventing oligomerizations and inhibiting decarbonylation steps that are directly related to the catalytic deactivation by poisoning.

Phosphotungstic acid (HPW) and silicotungstic acid (HSiW) were tested as homogeneous and as heterogeneous catalysts (after immobilized on different supports as high surface area graphite -HSAG500-, montmorillonite -MMT- and alumina -Al₂O₃-) for the in situ transesterification of sewage sludge lipids. Both catalysts exhibited similar performance in homogeneous phase, with slightly higher biodiesel yield for HPW. When the different supports were tested with HPW, the maximum yield obtained follow the trend: MMT > HSAG500 > Al₂O₃, but a greater leaching of the heteropolyacid (HPA) was observed with MMT. Therefore, HSAG500 showed the best results with a good FAMEs profile. The percentage of active phase was optimized from 1 to 40%, reaching the optimum at 10%. A more heterogeneous surface is obtained with larger quantities, also favouring the HPA leaching. The reaction temperature and the use of sonication as pre-treatment were also optimized. The best results were obtained after sonication with HPW-HSAG500 (10%) as catalyst, catalyst/sludge ratio 1:2, MeOH/sludge ratio 33:1, 120 °C and 21 h of reaction time with a maximum biodiesel yield of 31.1 % (FAMEs/lipids). In view of the results obtained HPW supports on HSAG500 offers a novel alternative as heterogeneous acid catalyst for in situ transesterification using sewage sludge as raw material.