Sodium borohydride hydrolysis-mediated hydrogenation of carbon dioxide, towards a two- step production of formic acid

Abstract

One of the levers to mitigate the amount of carbon dioxide (CO2) released into the atmo-sphere is to capture and use it as cheap, abundant, and safe carbon source, that is, as feedstock in order to produce valuable chemicals like formic acid (HCOOH) that is known to have the potential for high environmental impact reduction. It is in this context that we have developed a two-step process to produce HCOOH by hydrogenation of CO2 at ambient conditions while using sodium borohydride (NaBH4) in aqueous solution. Our process can be described as follows. In a first step, CO2 is bubbled in an aqueous solution of NaBH4; nickel-catalyzed hydrolysis of NaBH4 takes place and the reaction is accelerated in the presence of CO2, resulting in the formation of, among other products, sodium formate (NaHCOO) and a HCOO group containing borate B(OH)2(OOCH). In a second step, these products are dissolved in alkaline aqueous solution and heated at 130 degrees C; in such condi-tions, HCOOH is produced and recuperated as distillate, and a solid 'residue' consisting mainly of Na2CO3, NaHCOO and NaB(OH)4 is recovered. Our two-step process aiming at capturing and transforming CO2 has proven to be effective, importantly at ambient con-ditions. Our main results and the remaining challenges are reported and discussed herein.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.