Synthesis of biochar-doped MgO catalyst for highly efficient conversion of glucose into formic acid at low temperatures

Abstract

Formic acid (FA) is not only a significant platform chemical but also a promising candidate for hydrogen storage. Although homogeneous catalysts are commonly employed for the conversion of carbohydrate biomass into FA, which often come with substantial costs and inadequate reusability. It is noteworthy that there has been an increasing focus on the development of heterogeneous catalysts in this area, which aim to address these limitations and offer advantages such as easier separation and better reusability. Herein, an eco-friendly and efficient method for the catalytic conversion of glucose to FA by utilizing a biochar-MgO (BC-MgO) catalyst, which is prepared through pyrolysis of coconut husk biochar impregnated with magnesium chloride (MgCl2), is proposed. The FA yield at 74.6% is attained from glucose at 60 °C within only 3 h, utilizing a mere 0.1 g of catalyst and hydrogen peroxide (H2O2) amount of 100%. In conjunction with random forest (RF) algorithms and box-behnken experimental designs, further optimization resulted in an increased yield of 79.1%, with a selectivity of 82.7%, in only 3.8 h at 67 °C, employing 0.1 g of catalyst amount and 125% H2O2 amounts. Notably, the BC-MgO catalyst retains its catalytic efficiency over multiple cycles, only requiring a simple straightforward regeneration procedure. The mechanism underlying the glucose conversion to FA reaction system is demystified via kinetic modeling, time-gradient studies, and model compounds experiments. Life cycle assessment (LCA) indicates that when used for glucose conversion to FA, BC-MgO catalysts generate lower CO2 emissions than traditional homogeneous catalysts such as LiOH. Concurrently, an operation cost analysis indicates that operation cost of FA production from glucose is 4.1 $/kg with the BC-MgO catalyst, which is lower than LiOH catalyst (7.5 $/kg), evidencing the dual advantage of economic viability and an improved environmental impact inherent to this novel process.