Enzymatic Conversion of Carbon Dioxide to Methanol by Dehydrogenases Encapsulated in Sol—Gel Matrix

Abstract

Introduction Due to the abundance of CO2 as the major greenhouse and the most oxidized form of carbon, the efficient utilization of CO2 has aroused much interest from fundamental research to application application. Herein, we report a novel and promising approach to convert carbon dioxide into methanol through consecutive reduction catalyzed by three different dehydrogenases. The whole process consists of three steps: reduction of CO2 to formate catalyzed by formate dehydrogenase (FateDH), reduction of formate to formaldehyde by formaldehyde dehydrogenase ( FaldDH), and reduction of formaldehyde to methanol by alcohol dehydrogenase (ADH). Reduced nicotinamide adenine dinucleotide (NADH) acts as a terminal electron donor for each dehydrogenase-catalyzed reduction. It is now well established that a wide variety of enzymes retain their characteristic reactivities and chemical functions when they are confined within the pores of the silica sol-gel derived matrix. The porosity of sol-gel glasses allows small molecules and ions to diffuse into the matrix while the enzymes remain physically trapped in the pores, and thus resulting in an enhanced probability of reaction due to an increase in local concentration of substrates within the nanopores. Our experiments demonstrated that when the above-mentioned three enzymes are encapsulated in the silica sol-gel matrix, the yield of methanol is considerably increased as compared to that in solution phase.