Introducing\na Second Liquid Phase in the Carbon Dioxide\nHydrogenation to Formic Acid: Impact on Catalytic Conversion in Ru-Catalyzed\nSystems

The synthesis of formic acid (FA) from CO<sub>2</sub> and hydrogen\nis a renewable pathway as an alternative to fossil-based indirect\ncarbonylation of water and offers the possibility of reducing the\ncarbon footprint of the chemical industry. However, scaling up homogeneously\ncatalyzed CO<sub>2</sub>-based FA production requires effective catalyst\nseparation, necessitating advanced methodologies to address the challenges\nspecific to homogeneous catalysis. Liquid/liquid multiphase catalysis\nis a promising solution, but its complete impact remains elusive.\nIn this study, the influence of a second liquid phase on catalytic\nconversion was explored using a specially designed miniplant in combination\nwith a model reaction system. A <i>cis</i>-[Ru(1,1-bis(diphenylphosphino)methane)<sub>2</sub>Cl<sub>2</sub>] catalyst, methyl isobutyl carbinol solvent,\nand triethylamine as a thermodynamically compensating agent were employed.\nThe investigation of factors influencing FA conversion in a monophasic\nsystem was conducted by varying parameters, such as temperature, pressure,\ngas substrate ratios, and liquid phase composition. Based on this,\na study of the main variables of the biphasic system formed by introducing\nan aqueous phase was carried out. It was found that the introduction\nof water as a second phase mitigated the catalytic inhibition of FA\nformation observed in the monophasic system, suggesting a role in\nrestoring the activity of the catalyst species. Therefore, for this\nreaction, the advantages of the separation process in biphasic reactions\nusing water are further clarified.