Controllable Frabrication Of Active-sites Of Ni-based Catalysts For Steam Reforming Of Heavy Hydrocarbon

Hydrogen,as a potentially attractive energy in the future,has become a hot energy because of its clean energy and high energy.Steam reforming of heavy hydrocarbons for hydrogen production has attracted much attentions since the process could be obtained on-site hydrogen with highly productivity.Ni-based catalysts have been widely applied in steam reforming process due to its highly activity in C-C and C-H band scission and its low price.However,since steam reforming of heavy hydrocarbon with complex structure and the presence of sulfide take places at high temperature,involves types of reactions and present several carbon formation pathways,it makes lowsteam reforming activity and deactivation of Ni-based catalysts due to coking,sintering and sulfur poisoning.Consequently,that how to fabricate and tune the active sites of Ni-based to improve the steam reforming activity,carbon resistance,sintering resistance and sulfur resistance has become an emphasis in steam reforming of heavy hydrocarbon for hydrogen production.This dissertation focuses on tuning active sites of Ni/Al₂O₃ catalyst,the frabrication and optimization design of active sites of NiPt bimetallic catalysts,as well as the effect of NiPt alloy on the sulfur resistance of NiPt bimetallic catalysts.The main research contents are as follows:Firstly,ALD-Ni/Al₂O₃ catalysts with main Ni⁰（none Ni Al₂O₄ species）species were prepared by atomic layer deposition through tuning metal-support interaction.The result showed that the n-dodecane TOF of ALD-Ni/Al₂O₃catalyst could be reached 478h^-1,but deactivations from coking and sintering were also observed,which was due to the weak metal-support interaction of Ni⁰ species.Ce O₂ modified ALD-Ni/Al₂O₃catalysts enhanced metal-support interaction,resulting in high Ni^x+species percentage and stabilizing particle size.In addition,Ce O₂ promoted the conversion of H₂O and reduced carbon deposition,thus significantly inhibiting the deactivation degree decreasing from 66%to 8%with a S/C ratio of 4 at 700°C.Secondly,NiPt bimetallic catalysts were prepared by impregnation method.Active sites were frabricated and optimized through adding different Pt loading and tuning the surface of NiPt bimetallic catalysts.The results showed that the addition of Pt enhanced the conversion of n-dodecane and H₂ molar yield.Specifically,when Pt loading reached1.0 wt.%,the H₂ molar yield could be reached around 23 mol _H2/mol _C12H26 over Ni-Pt/Al₂O₃（Ni-rich surface）catalyst.It was also found that the presence of NiPt alloy in these NiPt bimetallic catalysts,leading to smaller particle size and more moderate metal-support Ni^x+species from the conversion of Ni Al₂O₄ species.Furthermore,Ni enriched surface is favorable for the formation of CH_x group through C-C band and C-H band scission.In addition,Ni^x+species enhanced the adsorption of H₂O and facilitated H₂O dissociation.Moreover,NiPt alloy promoted the surface reaction of CH_x.Finally,in view of alloy effect,Ni-Pt/Al₂O₃ catalysts were investigated in steam reforming of sulfur containg heavy hydrocarbons.It was found that only 14%deactivation degree and 18 mol _H2/mol _C12H26 H₂ molar yield was observed over Ni-Pt/Al₂O₃ catalyst under 50 ppm thiophene,which was superior to the same parameters of Ni/Al₂O₃ catalysts,indicating the Ni-Pt/Al₂O₃ catalyst showed certain of sulfur resistance,inferring that the presence of NiPt alloy leads to the decline in the adsorption of H₂S,thus enhancing the sulfur resistance.