The Preparation Of Nickel-Based Bimetallic Catalysts With Macro/Meso Bimodal-Structure And Study On Catalytic Performances In Dry Reforming Of Methane

Reforming of methane with carbon dioxide to synthesis gas has potential industrial application value because it can convert two greenhouse gases at the same time and obtain synthesis gas,which is an important chemical raw material.Nickel-based catalysts are inexpensive and have highly catalytic activity,which are widely used in reforming of methane with carbon dioxide reaction.However,it is easy to deposit carbon in the reaction process,which limits its industrial application.In this study,the evaporation-induced self-assembly(EISA)method was used to prepare a series of macro/meso bimodal structure by adding mesoporous template triblock copolymer(P123)and macroporous template polystyrene microspheres(PS,100 nm),respectively.The synergistic effect of the bimetallic and bimodal structure over nickel-based catalyst was investigated for its catalytic performance of the reaction,in order to improve the catalytic activity and carbon deposition resistance of the nickel-based catalyst.Research content and research progress of the study mainly include the following three aspects:The first part:A series of nickel-iron bimetallic catalysts with macro/meso bimodal structure were prepared by one-pot method.The catalytic performance for dry reforming of methane reaction(DRM)was investigated.Results showed that bimetal nickel and iron formed a NiFe alloy phase after reduction,and its strong interaction was conducive to improving the stability of active components,thereby increasing the catalytic activity of catalyst;macropores in bimodal structure can increase the diffusion rate of reactant and product molecules,so that the amorphous carbon produced by the reaction can be quickly eliminated by gasification.The bimodal structure catalyst with an iron-nickel ratio of 0.5(NF0.5-M100-MA)had the highest catalytic activity.After 100 h of reaction,the conversion rates of CH4 and CO2 were 76.8%and 85.6%,respectively;the amount of carbon deposition after 100 h reaction was only 1.8%(the amount of carbon deposition over the mesoporous structure catalyst NF0.5-MA after 100 h reaction was 8.3%),and most of the carbon deposition was amorphous carbon,which was highly unstable and easy to eliminate.It showed that the bimodal structure and bimetal had a synergistic effect on the dry reforming of methane reaction.The second part:One-pot method was used to prepare nickel-cobalt bimetallic catalyst with macro/meso bimodal structure,and the effect of different cobalt-nickel ratios on the catalystic performance was investigated.Results showed that the catalyst had the best performance when Co/Ni0.5(NC0.5-M100-MA).After 100 h of reaction,the conversion rates of CH4 and CO2 were 73.1%and 81.6%respectively;at the same time,compared with other catalysts,the carbon deposition was significantly reduced to 3.6%,and most of the carbon deposition was amorphous carbon.Mainly due to the oxygen affinity of Co,it can increase the oxygen concentration on the catalyst surface,promote the gasification of carbon deposition,and then improve the carbon deposition resistance of the catalyst.The third part:Due to the decrease in the activity of the nickel-cobalt catalyst with macro/meso bimodal structure,Mn was doped in it,and the Ni-Co interaction in the catalyst was changed in order to improve the stability of the catalyst.One-pot method was used to prepare macro/meso bimodal nickel-cobalt catalysts with different Mn content.Results showed that the conversion rates of CH4 and CO2 reached 76.8%and 85.1%respectively after 100 h reaction of the 0.5Mn catalyst.Compared with the initial reaction activity,there was almost no decrease,and with the increase of Mn content,the amount of carbon deposition on the catalyst gradually decreased.The addition of Mn reduced the particle size of the active component:X-ray diffraction,transmission electron microscopy and other characterizations showed that the addition of Mn reduced the particle size of the active component NiCo from 9.9 nm to 7.7 nm,which can effectively inhibit the growth of carbon nuclei and suppress the carbon deposition.When the Mn content was 1%,the amount of carbon deposition was only 1.8%.