Synergy between oxides of Ni and Ca for selective catalytic lactic acid synthesis from glycerol in a single step process

Abstract

Single-step selective catalytic dehydrogenation of glycerol to lactic acid requires a catalyst with strong dehydrogenation and hydration capabilities. A multi-component catalyst consisting of an alkaline earth metal and assisted by a transition metal is deemed essential to achieve yield lactic acid in this multi-step reaction. A series of NiO/CaO catalysts with different Ni/Ca ratios were synthesized via a co-precipitation method and tested for their catalytic activity. The physicochemical properties of the catalysts were studied through TGA, SEM, N2-adsorption, CO2-TPD and XRD analyses. The NiO particles were relatively smaller than those of CaO to enable their deposition on the surface of the latter. High amounts of basic sites of more than 4.84mmol/gcat were detected on the NiO/CaO catalysts. The lactic acid yield was strongly influenced by the molar ratio of the NiO/CaO catalysts due to their improved dehydrogenation and hydration capabilities. The synergy between NiO with CaO in the catalyst was also elucidated. The 0.43NiO/CaO catalyst exhibited desirable activity with 41.4% lactic acid yield at 89.3% glycerol conversion. A catalyst loading of 15wt. %, a reaction temperature of 290°C and 1.5h of reaction time were needed to achieve this conversion. Thus, the combination of NiO/CaO resulted in the synergy towards achieving better lactic acid yield in this selective conversion to lactic acid. However, accurate control of the reaction was critical as the intermediates and lactic acid were highly reactive to participate in other side-reactions.