Synthesis And Reaction Study Of MoS₂ Catalyst Induced By Methane/propane In H₂S Atmospher

With the increasing demand for energy worldwide and the depletion of traditional fossil fuels,people are turning their attention to the development and utilization of acid natural gas with abundant reserves.Sour natural gas contains low-carbon alkanes（CH4,C3H8）and non-hydrocarbon compounds（CO2,H₂S）.Among them,CH4 and CO2 are the greenhouse gases that cause global warming and are generally converted into more valuable syngas through dry reforming of methane.However,a small amount of toxic H₂S acid gas is also present in sour natural gas,which can lead to the poisoning and deactivation of most metal and metal oxide catalysts,slowing down the development and utilization of sour natural gas to some extent.In recent years,MoS₂ catalysts have been widely used in sulfur-containing catalysis because of their superior sulfur resistance properties.It is a sulfide formed by covalent bonding of Mo and S atoms,usually showing a hexagonal layered structure,which can be specifically divided into substrate and side.Usually unsaturated Mo atoms are not uniformly distributed on the surface of MoS₂ plates,and most of them are enriched at the edges of MoS₂ sides.It has been shown that fewer layers of MoS₂ plate sides will expose more unsaturated Mo sites to achieve the expected catalytic performance.Therefore,how to obtain MoS₂ catalysts with fewer layers becomes a difficult research problem at present.Based on this,the following research work was carried out in this thesis using MoS₂ catalysts.1.Three morphologies of Al₂O₃ supported Mo source catalysts were prepared,and their catalytic performance in the CH₄-CO₂-H₂S reaction system was investigated after high-temperature vulcanization treatment.It was found that the activity of the catalysts was as follows:MoS₂/Al₂O₃-F>MoS₂/Al₂O₃-C>MoS₂/Al₂O₃-OM.Through characterization analysis,it was found that there were differences in the reduction degree of the active components（Mo,S）,the sulfuration degree of the catalysts,and the phase structure of the catalysts on these three catalysts,resulting in differences in the activity of the catalysts.In addition,the promotion mechanism of H₂S was preliminarily explored.It was found that the in-situ introduction of H₂S during the CH₄-CO₂ reforming process continuously sulfides the catalyst,and to some extent,induces a reduction in the number of layers of MoS₂,exposing more edge unsaturated Mo sites,thereby improving the efficiency of the catalytic reaction（CH4:9.7%-23.2%,CO2:22.4%-54.3%）.Subsequently,by changing the concentration of H₂S in the reaction system,combined with characterization,the exact catalytic effect of H₂S was further confirmed.2.The above experimental investigations indicate that the in situ introduction of H₂S in the CH₄-CO₂ reforming reaction induces a change in the number of layers in the MoS₂ catalyst.Several MoS₂ catalysts were prepared and evaluated for their activity and H₂S sensitivity,and the best catalyst was selected to investigate the effect of their specific atmosphere on the catalyst structure.The catalysts were subjected to different temperatures（400,600,800℃）and atmospheres（H₂S/H₂,CO2/H₂S/H₂,CH4/H₂S/H₂,CH4/CO2/H₂S/H₂）to sulfide the catalysts.It was confirmed by characterization that the presence of CH4 in H₂S atmosphere may produce competing adsorption and the interaction forces formed will weaken the stacking of MoS₂ layers,resulting in MoS₂ catalysts with few or even single layers.Meanwhile,replacing CH4 gas with C3H8 gas was found to produce the same effect.It shows that the presence of light alkanes in H₂S atmosphere affects the stacking tendency of MoS₂ layers.Therefore,the application of MoS₂ catalyst to the CH₄-CO₂-H₂S reaction system well promotes the activation of CH4 and CO2 under H₂S atmosphere,further accelerating the development and comprehensive utilization of sour natural gas.Meanwhile,CH4 and C3H8 in sour natural gas will affect the stacking tendency of MoS₂ layers in the sulfidation process,which provides a new opportunity to prepare MoS₂ catalysts with fewer or even single layers.