Co/C-N Catalytic CO₂ Hydrogenation To Methanol

With the acceleration of the industrialization process,the CO₂ content in the air increased sharply,which led to global warming and some other serious environmental problems.The conversion of CO₂ into high-value energy is the hot topic of current research.Hydrogenation of CO₂ into methanol is currently a superior approach.Methanol is a clean energy fuel and basic chemical raw material.There are still many difficulties in the catalysts research of methanol synthesis,such as the activation of CO₂,low selectivity,and poor catalyst stability.At present,the development of methanol synthesis catalyst with high activity,high selectivity and good stability is one of the hot spots of research.In this paper,ZIF-67 was used to ZIF-aggregation as a precursor of a nitrogen-doped carbon-supported cobalt catalyst,Co@Co₃O₄/C-N and Co-Mo₂C/C-N catalysts were obtained with calcination at nitrogen atmosphere.The former was partially oxidized by oxidation treatment of Co/C-N catalyst.Co@Co₃O₄/C-N catalyst was studied withdifferent roasting temperature,different oxidation time and oxidation temperature.Co-Mo₂C/C-N catalysts was studied with the effects of the addition of Mo₂C,Co metal modification and different molar ratio of cobalt and molybdenum on the catalytic performance of methanol synthesis catalysts.The specific research work was as follows:（1）Using Co（NO₃）₂·6H₂O as the cobalt source,2-methylimidazole as the carbon source and nitrogen source,a nitrogen-doped carbon supported cobalt-based catalyst（Co/C-N）was prepared by ZIF-polymerization.The Co@Co₃O₄/C-N catalyst was prepared by partial oxidation of Co/C-N in air under different conditions.It was found that the Co/C-N catalyst was calcined at 600℃,the particle size of the metallic Co was small and the specific surface area was large.At the same reaction temperature,the stability of Co/C-N600 was good,and no obvious deactivation was occurred within 50 h.Compared with Co/C-N-600,the CO₂ conversion rate of Co@Co₃O₄/C-N decreased,and the selectivity of methanol increased with the decrease of metallic Co content.At 220℃reaction temperature,the catalyst has good stability and no significant deactivation within 50 h.The CO₂ conversion rate of the Co@Co₃O₄/C-N（220,2 h）catalystwas 18.6%.The highest yield was 2.0 mmol·g^-1_cat·h^-1.（2）Co（NO₃）₂·6H₂O was used as the cobalt source,Zn（NO₃）₂·6H₂O was used as the zinc source,and 2-methylimidazole was combined to synthesize the precursors ZIF-8 and ZIF-67.A Co-Mo₂C/C-N catalyst was prepared by equal volume impregnation method using a molybdenum acetylacetonate（MoO₂（acac）₂）molybdenum source.It is found that the proper Co/Mo ratio would enhance the interaction between Co and Mo₂C in the reaction,reduced the selectivity of methane,and increased the selectivity of CO and methanol.Co-Mo₂C/C-N-1 has a proper Co/Mo ratio,the CO₂ conversion rate was 8%at 260°C,and the yield of methanol was 3.4 mmol·g^-1_cat·h^-1.