Study On The Effect Of Sulfurization Atmosphere On The Performance Of Sulfur-resistant Pd₄S/SiO₂ Catalyst

Methane as the main component of natural gas is a viable bridge between traditional energy and renewable energy sources and is now playing an increasingly important role on a global scale.At present,the supported palladium catalyst has attracted much attention due to the best performance in the catalytic oxidation of CH₄,but natural gas is a complex gas mixture,which usually contains some traces of sulfur-containing substances,such as H₂S,SO₂,etc.Sulfur species are the natural enemies of most metal catalysts,especially palladium catalysts.In the reaction,PdO catalyst can not resist the poisoning of sulfur-containing substances in natural gas and is easily poisoned and deactivated.Previous studies on the poisoning of supported palladium catalysts against sulfur-containing substances have only temporarily slowed down the rate at which the catalyst is poisoned by sulfur-containing substances,and have not really enabled the catalyst to the ability of sulfur-tolerance.Based on this,this paper designs a catalyst with true sulfur-tolerance from a new perspective.In view of the S and O are located in the adjacent positions of the same main group in the periodic table,they have similar properties.This experiment decided to select Pd_xS_y species instead of PdO as the active species of the catalyst,and the carrier used acidic carrier SiO₂ which does not adsorb sulfur species.Therefore,this paper attempts to design a new Pd_xS_y/SiO₂ catalyst to be applied to the catalytic oxidation of CH₄.Pd_xS_y species are generally produced by gas phase sulfuration in H₂S atmosphere,but gas phase sulfuration is difficult to obtain a single Pd_xS_y species due to temperature,which makes it difficult to study this topic.Therefore,in this work,we would like to present a new procedure for the preparation of Pd_xS_y/SiO₂ catalysts via aqueous bubble sulfuration of Pd/SiO₂ with H₂S mixture.Compared with the gas phase sulfuration method,the method has a milder sulfuration temperature,and it is easier to prepare a single Pd_xS_y species,which is beneficial to explore the relationship between palladium sulfide species and catalyst activity.This paper will study the effects of various concentrations of sulfuration atmosphere,temperature and rate on the catalyst.The sulfur resistance,catalytic activity and stability of Pd_xS_y species in CH₄ catalytic oxidation were investigated.The catalysts were characterized by XRD,XPS,TEM,TPR,TPO,etc.The study found that a single Pd₄S species was obtained by liquid phase sulfuration of the supported palladium catalyst.When liquid phase sulfuration was carried out under H₂S/H₂ atmosphere,the content of Pd₄S in the catalyst increased first and then decreased with the increase of H₂S concentration.The content of Pd₄S was the highest and the catalytic activity was the best when the concentration of H₂S was 7%.When liquid-phase sulfurization of catalyst is carried out in H₂S/H₂?10%?sulfurization atmosphere with different flow rates,the dispersion of catalyst will be affected.When the flow rate is 30 ml/min,the dispersion of the prepared catalyst is the best and its catalytic performance is the best.A single Pd₄S species can also be obtained by liquid-phase sulfurization in H₂S/N₂?10%?atmosphere.With the increase of sulfurization temperature,the sulfurization degree of the catalyst increases.When the sulfurization temperature reaches 100 ⁰C,the catalyst almost completely sulfides into all crystal planes of Pd₄S species.By investigating the catalytic activity of the catalyst in the catalytic oxidation of CH₄ in the presence of sulfur-containing substances,it can be known that the Pd₄S/SiO₂ catalyst has a real sulfur poisoning resistance.The sulfur-tolerance and catalytic activity were completely dependent on Pd₄S,and independent on other palladium species.First,Pd₄S can protect the coexisting PdO from being poisoned by sulfur species,giving the catalyst a true sulfur tolerance.Secondly,Pd₄S has catalytic activity as much as PdO.The content of Pd₄S solely determined the catalytic activity of the catalyst with little impact from the coexisting PdO.Third,Pd₄S had sufficient oxidation stability under reaction conditions.In view of the great stability and the excellent sulphur-tolerant property,the Pd₄S/SiO₂ catalyst will be a very promising high performance sulfur-tolerant catalyst.