Preparation Research Of Fe-based Catalysts For CO₂ Hydrogenation

After the industrial era,the carbon dioxide?CO₂?content has risen remarkably in the atmosphere.Nowadays,the high CO₂ content has seriously aggravated the greenhouse effect and caused extremely damage to the ecosystem and the environment on which humans depend.CO₂ is not only a greenhouse gas,but also an important carbon source for the production of organic chemicals,materials and carbohydrates such as food.CO₂ can be used to synthesize various chemicals,materials and fuels.When renewable energy such as solar energy is used as the energy input for chemical treatment,it is of great significance for sustainable development.The catalytic conversion of CO₂ is an important way to utilize CO₂.In the catalytic hydrogenation of CO₂,Fe-based catalysts have been widely studied due to low price and high activity.In this work,different crystal forms of the catalyst were prepared.The addition of Pd,K,Cu and Al changed the structure and chemisorption of the catalyst.The effects of different sugars added to Fe-based catalysts and their performance of CO₂hydrogenation were investigated.The results have been obtained as follows:Pure?-Fe₂O₃ was prepared by a two-step process.First,tartaric acid and Fe?NO₃?₃·9H₂O were dissolved in water,and then the stirred mucilage was dried and calcined in air,then Pd and K were added to Fe₂O₃ by impregnation method.The effect of Pd or K on the reduction of Fe₂O₃,H₂ and CO₂ adsorption is different,but there is a synergistic effect when Pd and K?catalyst PKF?are added together to the catalyst.The addition of K improved the reduction of Pd on Fe₂O₃ and increased the adsorption of CO₂ on the catalyst PKF below 300?.The synergistic effect made PKF have the highest C₅₊selectivity for CO₂ hydrogenation at 235?.The FeAl precursor was prepared by coprecipitation method.Sucrose was added in different ways during the coprecipitation process,and K and Cu were added by impregnation method.Because Pd has strong hydrogenation ability and produces high CH₄ selectivity,it is replaced by Cu.The addition of sucrose changes the structure and catalytic activity of the catalyst.Different ways of addition have different effects on the hydrogenation performance of CO₂.When sucrose is added to the nitrate solution,the catalyst has higher CO₂ hydrogenation activity.It is believed that sucrose hydrolysis plays an important role in the preparation process.From the XRD results,?-Fe₂O₃ appeared by increasing the temperature,indicating that the glucose and fructose produced by sucrose hydrolysis can promote the formation of?-Fe₂O₃.With the understanding to sucrose hydrolysis,Fe-based catalysts were prepared by adding fructose and glucose directly in the co-precipitation process.The results of XPS characterization showed that the binding energy of Fe 2p in the dried sample shifts toward the low binding energy,indicating that Fe³⁺is reduced to Fe²⁺due to the presence of reducing glucose and fructose during the drying process,and then Fe²⁺is oxidized again to Fe³⁺during the calcination.which promoted the formation of metastable?-Fe₂O₃,rather than thermodynamically stable?-Fe₂O₃ phase.Compared with the catalysts added only glucose or fructose,it can be seen from XRD that adding fructose is more beneficially to form?-Fe₂O₃,indicating that fructose is more reducible than glucose.The study find the most active catalyst?FG-C?was prepared by adding fructose and glucose into the precipitate.Under the reaction conditions of H₂:CO₂=3:1,6.0 L/?h·g-cat?,1.6 MPa,235?,the CO₂ conversion is 30.3%,and the C₅₊selectivity is 52.2%.