Direct Conversion of Microalgae Biomass to Formic Acid under an Air Atmosphere with Soluble and Solid Mo-V-P Heteropoly Acid Catalysts

The present work demonstrates high potential of Parachlorella kessleri IC-11 microalga biomass for the production of biogenic formic acid under hydrothermal conditions and an air atmosphere. Homogeneous and heterogeneous catalytic approaches were applied and compared. The experiments were carried out in the presence of soluble H5PMo10V2O40 and solid [(C4H9)(4)N](3).5H0.5PMo11VO40 bifunctional catalysts. The influence of reaction temperature and catalyst loading on the formic acid formation was revealed. Experimental data demonstrated that the microalgae biomass transformation to formic acid was limited by biomass depolymerization and hydrolysis processes, not the oxidation of intermediates to formic acid. H5PMo10V2O40 allowed for formic acid to be obtained with better yields compared to [(C4H9)(4)N](3.5)H0.5PMo11VO40. Yields of 49 and 30 wt % of the target product were achieved over H5PMo10V2O40 and [(C4H9)(4)N](3.5)H0.5PMo11VO40, respectively. The solid catalyst demonstrated high stability in seven runs of the reaction at least while the activity of soluble heteropoly acid declined in the fifth reaction cycle.