Since the first report [10], until today, there is no available information about catalysts for HDO better than Ni-Mo and Co-Mo. Although, they are known as good deoxygenating catalysts for 20 years, recently, due to increasing interest in production of renewable diesel, numerous research groups have done studies on improving catalyst performance and understanding mechanism of HDO of fatty acids and their derivatives.

Nowadays the commonly used catalysts are sulfided Ni-Mo/y-Al2O3 and Co — Mo/y-Al2O3 [16-20]. Sulfided catalysts gave higher conversion and selectivity at lower temperatures, between 250 and 300°C (Table 6.1), compared to perfor­mance of the oxides which are more active at temperatures above 350°C [10]. Although sulfided catalysts are more active in deoxygenation, there is a threat of fast deactivation caused partially by leaching of sulfur from the catalyst (Table 6.1). Alternatively sulfur could be added to feedstock, but in that case it will cause contamination of the product—diesel fuel, which should be sulfur-free.

When comparing sulfided catalysts, in terms of activity and selectivity, sulfided Ni-Mo/c-Al2O3 outperformed Co-Mo/c-Al2O3 catalyst at lower temperatures (250-300°C) giving higher conversion and selectivity to hydrocarbons (Table 6.1) [11-13]. The data shows that the sulfided Ni-Mo/y-Al2O3 is the most suitable catalyst taking into account its selectivity and activity for HDO reaction at rela­tively low temperature.