| Nowadays,the global challenges such as climate change,the depletion of fossil energy and raw material resources,etc.,require us to solve the problem from a new angle.The use of natural oils and fatty acid hydrogenation to prepare fatty alcohols is green,sustainable and in line with people’s modern concepts of healthy and safe consumption.The traditional catalysts used in the hydrogenation of natural oils and fatty acids to prepare fatty alcohols mainly include unsupported catalysts such as Cu-Cr,Ni,Pd,and supported metal catalysts such as Al2O3,activated carbon,and various silicon molecular sieves.Unsupported catalysts have the shortcomings of small specific surface area and easy agglomeration,so they cannot fully contact the reaction substrate.However,ordinary supported catalysts can hardly tolerate long-term high temperature and high pressure and strong acid and alkali environments,and are prone to decrease in activity,deactivation,and even collapse and decomposition of the catalyst structure,which may pollute the product.So,it is significant to develop a simple,green,high-efficiency,hightemperature,acid-and alkali-resistant carrier catalyst system for selective hydrogenation of natural oils and fatty acids to prepare fatty alcohols.Graphite carbon nitride（g-C3N4）as a catalyst carrier with good thermal and chemical stability.Therefore,we loaded the commonly used hydrogenation active centers on g-C3N4,and prepared a series of hydrogenation catalysts for the hydrogenation of fatty acid esters.In this paper,methyl stearate was used as a model compound of fatty acid ester to investigate the catalytic effect of the catalyst.（1）We use the impregnation method to load commonly used hydrogenation metals（Pd,Ru,Ni,Co）on graphite phase carbon nitride,and the catalyst was synthesized.The prepared catalyst was characterized by TEM,XPS,XRD,N2 adsorption and desorption and so on.The characterization results showed that the structure of the g-C3N4 catalyst carrier was not destroyed after metal loading,and the metal was dispersed on the surface of the g-C3N4 uniformly.In addition,XRD and XPS characterizations showed that the metal active center was successfully introduced into the g-C3N4 carrier,and it mainly existed in the form of zero valence.The prepared catalyst was used in the hydrogenation reaction of methyl stearate,and the influencing factors on the hydrogenation reaction were investigated.The results show that the optimal conditions are: the metal loading is5%;the reaction temperature is 210 ℃;the hydrogen pressure is 5 MPa;the reaction time is 5 h;and the amount of catalyst is m（methyl stearate）: m（catalyst）= 20:1.Under these conditions,the hydroxyl value of the reaction product is 191 mg KOH/g.The reusability of the catalyst was also investigated under the optimal reaction conditions,and the used catalyst was characterized by TEM.The results show that the catalyst still maintains a good catalytic effect after being used repeatedly for 5 times.The transmission electron microscope image shows that the Pd metal nanoparticles are still relatively uniformly dispersed on the surface of the carrier after repeated use for 5 times.（2）In order to save costs and further improve the catalytic effect,Pd/Ni/g-C3N4,Pd/Co/g-C3N4,Pd/W/g-C3N4 carbon nitride-based bimetallic catalysts were synthesized.The catalyst was characterized by FT-IR,TEM,XPS,XRD,N2 adsorption and desorption etc.The results showed that the metal was successfully loaded on the g-C3N4 carrier,and the metal nanoparticles had good dispersibility and stability on the surface of g-C3N4;the introduction of metal not only did not destroy the graphite phase structure of g-C3N4,but also mostly existed in the form of zero valence.The synthesized catalyst was used in the hydrogenation reaction of methyl stearate.The reaction results showed that the optimal reaction conditions were: Pd metal loading was 3.5%,Ni metal loading was 1.5%,reaction temperature was 210 ℃,hydrogen pressure was 5 MPa,and reaction time was 5 h.The amount of catalyst was m（methyl stearate）:m（catalyst）=50:3.Under optimal conditions,the hydroxyl value of the reaction product was 201 mg KOH/g.The functional groups on the surface of carbon nitride are conducive to the dispersion of metal particles,and the basic sites on the surface are combined with the active metal,which enhances the adhesion of the metal,improves the catalytic activity of the metal,and thus contributes to the increase of the hydroxyl value of the product.The reaction process conditions were optimized by RSM,and the optimal process conditions for methyl stearate hydrogenation reaction were established: reaction pressure 5.37 MPa,catalyst dosage 0.074 g,reaction temperature 209.27 ℃,reaction time 5.42 h.Under these conditions,the predicted hydroxyl value of the product is 201.8 mg KOH/g,and the theoretical value is close to the actual value,so the model is reliable.In summary,in this paper,g-C3N4 was used as the carrier to modify it,and the mesoporous graphite phase carbon nitride loaded with monometal and bimetal was synthesized.Due to the unique advantages of mesoporous graphite phase carbon nitride,the metal is uniformly dispersed on its surface and has good stability,and the basic sites on the surface also enhance the adhesion and catalytic activity of the metal.A bimetallic catalyst was prepared by doping other hydrogenation metals on the basis of supporting Pd metal,and showed a more excellent hydrogenation effect.This article provided new ideas for the hydrogenation of fatty alcohols to prepare fatty alcohols and the catalytic hydrogenation of carbon nitrides,and provided an important basis for the development of environmentally friendly catalysis. |
