Biofuels are already part of the energy matrix in many countries because of their environmental and economic benefits. Ethyl biodiesel can be produced by various processes, the main one being transesterification of triglyceraldehydes and ethanol. The current technological challenge is to develop efficient heterogeneous catalysts, at low cost, non-polluting and recyclable to be used in this process. In this context, hydromagnesites Mg 5 (CO 3 ) 4 (OH) 2 ⋅4H 2 O modified with different cations (Ca 2 + , Zn 2 + , Cu 2 + , Ba 2 + ) and synthesized by co-precipitation are used as precursors of catalytic oxides calcined at 600°C. The biodiesel synthesis was conducted at 120°C for 12 h using 20% (w/w) of catalyst per mass of soybean oil and the ratio 1:20 (mol/mol) of soybean oil/ethanol. The alkyl esters formed were quantified by Gas Chromatography-Flame Ionization Detection (GC-FID). The transesterification reaction catalyzed by the reference oxide had a yield of 40%, whereas the best yield (80%) came from the hydromagnesite modified with 20% of Ca 2 + which also had the highest basicity/acidity ratio. After use in three reaction cycles, the catalyst with 20% Ca 2 + had no significant reduction in efficiency when it was washed with acetone and recalcined at 600°C, while the untreated catalyst only had a yield of 42%, showing the need for effective reconditioning.

.4H 2 O in different ratios Mg 2+ /M 3+ where M 3+ is Al 3+ , Ga 3+ or both was carried out by the coprecipitation method to be applied in the transesterification reactions for synthesis of ethyl biodiesel from soybean oil and ethanol. The reactions were processed for 12 hours at 120 °C at a molar ratio oil/ethanol (1/20) with 20% (m/m) of the catalyst in relation to the oil mass, and the products were quantified by GC-FID. With the introduction of Ga 3+ in the solid, some physicochemical characteristics of LDHs were kept based in the data from X-ray pattern diffraction (XRD), vibrational spectrometry (ATR-FTIR), and scanning electron microscopy (SEM), but changes from thermogravimetric analysis (TGA), superficial area (BET), and the acidity/basicity properties were observed. Typical hydrotalcite with Mg 2+ /M 3+ = 3 was used as reference material and reach 45.1% of biodiesel conversion. Although the best conversion result (77.6%) was reached from the solid without Ga 3+ and with Mg 2+ /M 3+ ratio 4/1, there is an interesting correlation between the catalytic activities and the physicochemical properties of the solids with Ga 3+ and their respective homologous materials as discussed in this work.Keywords: ethyl biodiesel; bioenergy; hydrotalcites; metal oxides; heterogeneous catalysis. INTRODUÇÃOO biodiesel é um biocombustível composto por mistura de ésteres alquílicos produzidos a partir de álcoois de cadeias curtas, principalmente metanol e etanol, e glicerídeos graxos de origem vegetal ou animal, 1 e reconhecidamente causa menos impacto ambiental que o petrodiesel. Dados divulgados em 2016 pelo Ministério de Minas e Energia indicam que as principais matérias-primas graxas empregadas no Brasil são: óleo de soja (78%), gordura bovina (19%), óleo de algodão (2%), e outros óleos (0,9%). 2 Segundo a ANP (Agência Nacional do Petróleo, Gás Natural e Biocombustíveis), 3 em 2008, a adição de 2% de biodiesel ao petrodiesel passou a ser obrigatória, aumentando para 4% em 2009, 5% em 2010 e 7% em 2014. A produção nacional em 2015 atingiu 3,9 milhões de litros, e o governo brasileiro autorizou o uso voluntário de até 20% de biodiesel em frotas privadas, consumidores rodoviá-rios atendidos por ponto de abastecimento, e de 30% em transporte ferroviário, uso agrícola e industrial.Embora o uso de etanol seja menos frequente para a reação de transesterificação devido a sua higroscopicidade, o etanol é particularmente interessante para o Brasil em função da base industrial sucroalcooleira instalada e também pela baixa toxicidade deste álcool, comparada com a do metanol.A principal rota sintética comercial na produção de biodiesel envolve a reação de transesterificação entre matéria graxa e metanol por catálise alcalina homogênea usando NaOH ou KOH como catalisadores, pois apresenta baixo custo e elevados rendimentos, além da reação ocorrer em condições brandas de temperatura e sob pressão atmosférica. 4 No entanto esta rota apresenta fatores negativos como o não reaproveitamento do catalisador, produção de grande volume de ef...