Catalytic hydrothermal conversion of CO2 captured by ammonia into formate using aluminum-sourced hydrogen at mild reaction conditions

Hydrothermal CO2 Reduction by Glucose as Reducing Agent and Metals and Metal Oxides as Catalysts

“…Electrochemical and photochemical reduction for CO 2 hydrogenation have shown favorable results in overcoming this issue [ 9 ]. However, the high costs and low yields of these techniques [ 10 ] have led to the study of other alternatives such as the hydrothermal treatment in which CO 2 reduction takes places in water media at high pressures and temperatures [ 11 , 12 , 13 ]. In this process, water acts as hydrogen donor instead of H 2 , which is flammable and complex to store [ 14 ].…”

“…In most works, it is captured as NaHCO 3 , but it can be also in the shape of carbamates that are formed when CO 2 is captured by ammonia or amines. This process opens the possibility to connect carbon capture in basic solutions directly with the CO 2 conversion process, avoiding costly intermediate separation steps [ 12 , 15 ].…”

“…In order to reduce CO 2 , several metals have been suggested as CO 2 reductants: Zn [ 18 ], Fe [ 19 ], Mn [ 20 ], Mg [ 20 ] and Al [ 20 ] (efficiency: Al > Zn > Mn > Fe) [ 10 , 21 ] are mentioned as favorable for the process. Metallic catalysts metals such as Ni-ferrite [ 22 ], Ni nanoparticles [ 23 ], Ni [ 24 ], Raney Ni [ 25 ], Cu [ 20 , 21 ], Fe 2 O 3 [ 26 ], Ru/C [ 27 ] and Pd/C [ 12 , 27 ] can be used as-is or coupled with “zero-valent” metals to improve the reaction; however, the reduction of the metal after the process in order to recycle the material should be considered.…”

“…So far, there has been a number of studies in which the use of catalysts (Cu, Ni, Pd/C) in hydrothermal CO 2 reduction was carried out using metals as reductants (Zn, Mg, Al, etc.) [ 12 , 18 , 20 , 21 , 22 , 25 ]. This work studies, for the first time, the influence of different catalysts in the hydrothermal reduction of CO 2 by using an organic (glucose) as a reducing agent.…”

“…As CO 2 source, sodium bicarbonate (NaHCO 3 ) and ammonium carbamate (NH₄[H₂NCO₂]) were used. There are literature studies stating that ammonium carbamate is reduced by using metals or hydrogen [ 12 ], but this is the first time that the reduction is performed using organics containing an alcohol group. The main objective of the present work is to develop batch screening reactions to find the best catalyst that can improve the formic acid production, as well as lowering the temperature for the reduction reactions normally fixed at 300 °C in other works [ 29 ].…”