In the reaction system with NaBH 4 as a hydrogen donor, inhibiting the formation of hydrogen is the key to promote the efficient catalytic hydrogenation of CO 2 . In this study, nanoscale zero-valent nickel supported on carbon nanofibers (Ni 0 /CNFs) was fabricated as a catalyst for CO 2 hydrogenation in aqueous NaBH 4 solution. The characteristics of Ni 0 /CNFs were examined. By SEM, it was observed that spherical nickel nanoparticles were distributed homogeneously on the surface of strip-shaped carbon nanofibers. EDS mappings indicated that elements were evenly distributed on the catalyst, which might contribute to the uniform exposure of active sites. Via XRD, it was determined that all the diffraction peaks corresponded to the crystal face of nickel metal and that the absence of diffraction peaks of carbon nanofibers indicated that the crystallinity of the carrier was low. XPS study showed that nickel existed on the catalyst surface in two forms: zero valence metal and oxidation state. The effects of catalyst addition amount, NaBH 4 concentration, NaOH dosage, stirring rate on the yield of formate and hydrogen generation rate (HGR) were investigated. By optimizing the above parameters, the concentration of formate reached 150 mmol/L and the hydrogen production rate was 10.55 mL/min. Compared with the non-catalytic conditions, the concentration of formate increased by 57 % and the HGR decreased by 78 %. Moreover, the relationship between CO 2 hydrogenation and NaBH 4 hydrolysis was clarified. This research could enhance comprehension of CO 2 hydrogenation in aqueous NaBH 4 solution and contribute to the development of CO 2 capture and utilization storage technology. The significance of this study lies in clarifying the connection between CO 2 hydrogenation and borohydride hydrolysis in CO 2 catalytic hydrogenation technology.
Several tertiary amine solutions with different structures were tested in the integrated CO 2 capture and hydrogenation process in the presence of heterogeneous Pd/NAC catalysts. The tertiary amines of 3-dimethylamino-1,2-propanediol (3DMA-1,2-PD) and 3-diethylamino-1,2-propanedio (3DEA-1,2-PD) with high CO 2 absorption capacity and high formate yield were selected as suitable candidates as CO 2 capture and hydrogenation solvents. Under mild reaction conditions, a high formate yield of 68% was achieved when using 1 M 3DMA-1,2-PD solution with CO 2 loading of 0.5 mol amine/mol CO 2 . In addition, the physico-chemical properties of the Pd/NAC catalysts were examined and the reaction mechanism of CO 2 absorption and hydrogenation in the presence of Pd/NAC was proposed.
Sizhu Ren,Ziyuan Wang,Muhammad Bilal,Yuxiao Feng,Yunhong Jiang,Shiru Jia,Jiandong Cui
Multienzymatic conversion of carbon dioxide (CO 2 ) into chemicals has been extensively studied. However, regeneration and reuse of co-factor are still the main problems for the efficient conversion of CO 2 . In this study, a nanoscale multienzyme reactor was constructed by encapsulating simultaneously carbonic anhydrase (CA), formate dehydrogenase (FateDH), co-factor (NADH), and glutamate dehydrogenases (GDH) into ZIF-8. In the multienzyme reactors, cationic polyelectrolyte (polyethyleneimine, PEI) was doped in the ZIF-8 by dissolving it in the precursors of ZIF-8. Co-factor (NADH) was anchored in ZIF-8 by ion exchange between PEI (positive charge) and co-factor (negative charge), and regenerated through GDH embedded in the ZIF-8, thus keeping high activity of FateDH. Activity recovery of FateDH in the multienzyme reactors reached 50%. Furthermore, the dissolution of CO 2 in the reaction solution was increased significantly by the combination of CA and ZIF-8. As a result, the nanoscale multienzyme reactor exhibited superior capacity for conversion of CO 2 to formate. Compared with free multienzyme system, formate yield was increased 4.6-fold by using the nanoscale multienzyme reactor. Furthermore, the nanoscale multienzyme reactor still retained 50% of its original productivity after 8 cycles, indicating excellent reusability.
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