Mechanism Study Of Biodiesel Production By Hydrogenation Of Oils And Fats Catalyzed By Oxygen Vacancy-enhanced Nickel-iron Bimetallic Catalysts

Renewable biomass energy can replace fossil energy to produce corresponding chemicals and fuels,which has received extensive attention from researchers.The oil and inedible vegetable oil recovered from meal waste are used as raw materials to prepare First-generation biodiesel by Catalytic hydrotreatment technology,namely green diesel,which can solve the problems of high oxygen content,low calorific value,and high viscosity of the first-generation biodiesel,Can be used directly on the engine,and has broad development space in terms of clean energy.At present,the research focus of green diesel is on the development of new catalysts with high activity,high selectivity,low price and environmentally friendly.A large number of studies have shown that Ni-based catalysts have high application potential.However,Ni-based catalysts generally adopt impregnation method.It has limited loading and active sites,and the high reduction temperature of Ni-based catalysts results in low Ni dispersion.Therefore,compared with conventional catalysts,the catalytic activity of Ni is lower.The addition of metals and the use of functional carriers can effectively solve the above problems,which has become the focus of research on Ni-based catalysts in recent years.Therefore,in this paper,oleic acid is used as a grease model compound to prepare a Ni-Fe bimetallic catalyst by co-precipitation.The catalyst has ultra-high Ni loading,Fe is used as the catalyst promoter,and Al₂O₃,ZrO₂,CeO₂ is used as the catalyst Functional support.The activity of the above catalysts was tested in the oleic acid Catalytic hydrotreatment reaction,and the effects of Ni loading,Ni/Fe ratio and catalyst support on the catalyst activity were studied.Oxygen vacancies were introduced into Ni-Fe/Al₂O₃ catalyst by atmosphere deoxidation method,and the promotion effect of oxygen vacancies on the catalytic hydrogenation of oils and the competition mechanism between oxygen vacancies of ZrO₂ and Ni active sites in Ni-Fe/ZrO₂ catalyst were deeply studied.The main findings are as follows:1.Ni-Fe/Al₂O₃ bimetallic catalysts were prepared by impregnation method and co-precipitation method,and the activities of the two catalysts were compared in the oleic acid hydrogenation reaction.The results show that the Ni-Fe/Al₂O₃ catalyst prepared by the co-precipitation method produces a Ni-Fe alloy,and the conversion rate of the Ni-Fe/Al₂O₃ catalyzed oleic acid hydrogenation reaction prepared by the co-precipitation method is much higher than that prepared by the impregnation method For the Ni-Fe/Al₂O₃ catalyst,the yield of total alkanes is much higher than that of Ni-Fe/Al₂O₃,and the yield of stearyl alcohol is only 4.2%,which is much lower than that of Ni-Fe/Al₂O₃,thus indicating The catalytic performance of the catalyst prepared by the co-precipitation method is far better than that prepared by the impregnation method;2.Ni-Fe/Al₂O₃ bimetallic catalysts with different Ni loadings were prepared by co-precipitation method,and the catalyst activity was compared in the oleic acid hydrogenation reaction.The results show that increasing the loading of Ni can increase the activity of the catalyst.When the loading of Ni is 70 wt.%,the catalyst exhibits the maximum activity.When the loading of Ni is increased to 80 wt.%,that is,when there is no Al₂O₃ support,The catalytic performance is greatly reduced,which shows that the Al₂O₃ support promotes the activity of the Ni-Fe catalyst.In addition,the HDO/DC ratio of the Ni-Fe/Al₂O₃ catalyst product is less than 1,indicating that the Ni-based catalyst participates in the oleic acid hydrogenation reaction,the main reaction path is decarboxylation(DCX)and decarbonylation(DCN).3.Ni-Fe/Al₂O₃ bimetallic catalysts with different Ni/Fe ratios were prepared by co-precipitation method,and the catalyst activity was compared in the oleic acid hydrogenation reaction.The results show that increasing the ratio of Ni/Fe can increase the activity of the Ni-Fe bimetallic catalyst.When the ratio of Ni/Fe is 4/1,the activity of Ni-Fe/Al₂O₃ reaches the highest,but when there is no Fe in the catalyst,the catalyst The activity of the catalyst is very low,the conversion rate of raw materials is 76.0%,the yield of total alkanes is only 45.2%,and the yield of stearyl alcohol reaches 30.7%.This shows that when the active component is only Ni,the activity of the catalyst is very low.After that,the conversion rate of the raw materials instantly increased to more than 90%,indicating that the addition of Fe can effectively improve the catalytic performance of the Ni-based catalyst and increase the catalytic activity of the Ni-based catalyst in catalyzing the hydrogenation reaction of oleic acid;4.Catalysts with different supports(Al₂O₃-ZrO₂,Al₂O₃-CeO₂,Al₂O₃,ZrO₂,CeO₂)were prepared by the co-precipitation method.When the carrier of the Ni-Fe bimetallic catalyst is ZrO₂,the catalyst activity is the highest,and the raw material conversion rate is 98.6%,the total alkanes yield is as high as 93%,which is much higher than Al₂O₃(83.5%)and CeO₂(19.6%).For Al₂O₃ and ZrO₂,the bimetallic support does not improve the activity of the catalyst,while for CeO₂,the double The activity of metal supports is much higher than that of single metal supports.5.Oxygen vacancies are produced for Ni-Fe/Al₂O₃ bimetallic catalyst by atmosphere deoxidation method.After analysis,it is found that the Ni-Fe/Al₂O₃ catalyst calcined under 1%O₂/N₂ atmosphere has enriched oxygen vacancies and is rich in oxygen.The vacant Ni-Fe/Al₂O₃ catalyst has more suitable acid strength and acid content.The oxygen-rich vacancies and the ordinary Ni-Fe/Al₂O₃ bimetallic catalyst were applied to the oleic acid hydrogenation reaction,and their activities were co MPared.The results showed that the 70 wt.%Ni-supported catalyst was inferior to the calcination in a vacuum atmosphere.In addition to the activity,the activity in other atmospheres is very high,mainly because in the Ni-Fe/Al₂O₃catalyst supported by 70wt.%Ni,the synergy between the support and the active components has reached the best correlation,which shows that for Ni-Fe/For the Al₂O₃catalyst,when the loading of Ni is 70 wt.%and the ratio of Ni/Fe is 4/1,the activity of the catalyst is the highest.Changing the preparation atmosphere has little effect on the activity of the catalyst.The60 wt.%Ni-supported Ni-Fe/Al₂O₃ catalyst has the highest activity after calcination in1%O₂/N₂atmosphere.In the oleic acid hydrogenation reaction,the conversion rate of raw materials is as high as 98.7%,and the yield of total alkanes is as high as 97.2.%,much higher than the Ni-Fe/Al₂O₃ catalyst calcined under other atmospheres,indicating that the calcination of the catalyst by the atmosphere deoxygenation method can indeed generate oxygen vacancies,and the generated oxygen vacancies can react to the Ni-Fe/Al₂O₃ catalyst in the catalytic hydrogenation of oleic acid Played a role in promoting.6.Ni-Fe/ZrO₂ catalysts with different Ni content and ZrO₂ as the carrier were prepared by co-precipitation method,and the catalyst activity was compared in the oleic acid hydrogenation reaction to study the competition mechanism between oxygen vacancies and active sites.The results show that oxygen vacancies are easily formed in the Ni-Fe/ZrO₂ catalyst.When the loading amount of Ni is 60 wt.%,the Ni-Fe/ZrO₂catalyst exhibits the highest activity in the oleic acid hydrogenation reaction.For other Ni-Fe/ZrO₂ catalysts with Ni content,70 wt.%is the best Ni loading for CeO₂ support.Among the three carriers of ZrO₂,CeO₂,and Al₂O₃,only the ZrO₂ carrier has the best Ni content of 60 wt.%,and the other carriers have the best Ni content of 70 wt.%,indicating that the carrier has a great optimal loading of Ni.In the oleic acid Catalytic hydrotreatment reaction,the oxygen vacancy of the ZrO₂ carrier is related to the active site competition in the Ni-Fe/ZrO₂ catalyst.For the Ni-Fe/ZrO₂ catalyst,the oxygen vacancy is in the oleic acid hydrogenation reaction.Occupy the main position.