Construction And Performance Of Runi-based Novel Composite Catalyst For CO Selective Methanation In Hydrogen-rich Gas

With the development of proton exchange membrane fuel cells?PEMFCs?,hydrogen fuel cell vehicle?FCEV?has embarked on the test and commercial operation,people even proposed the objectives of"making the negative effect of the car infinite close to zero"and"bringing positive to society"by employing FCEV.However,the hydrogen fuels?especially reforming hydrogen-rich gas?has to be purified to eliminate the poisoning of Pt anode caused by a small amount of CO.CO selective methanation is regarded as an effective method for deep CO removal from hydrogen-rich gases.The key depends on the development of supported metal catalyst with high performance,high stability and good thermal conductivity in order to realize the fast CO methanation especially in low temperatures.The preparation technology of carbon nanotubes?CNTs?grown on Ni foam?NF?via chemical vapor deposition?CVD?technique was studied,the layered double hydroxides?LDHs?based Ru/TiO₂–MMO and RuNi/Al₂O₃–CNTs/NF catalysts,and metal–organic framework?MOF?based Ni/ZrO₂ catalyst were prepared and employed in CO selective methanation.The effect of preparation conditions on the morphology,structure,metal dispersion and catalytic performance of catalysts were characterized by XRD,TG-DSC,Raman?N₂ adsorption-desorption,SEM,TEM,H₂-TPR,CO-TPD,XPS and ICP-OES techniques.The methods for controlled preparation and the relationship of structure-activity of the catalyst was elaborated comprehensively.The main content of the paper was shown as follows.?1?NF supported Ni catalyst was successfully prepared and used to the fabrication of CNTs/NF composite via CVD technique.The effects of Ni/Al molar ratios,calcination temperature and reaction temperature on the diameter distribution of CNTs,and the catalytic performance were studied in detail.Results showed that the CNTs on NF followed base-growth mode,and the catalyst with Ni/Al molar ratio of0.1,calcination temperature of 550°C and reaction temperature of 650°C was preferable for simultaneously producing high hydrogen growth rate and CNTs with uniform size on NF.?2?A series of TiO₂–NiAl LDHs was successfully prepared via one-pot deposition method.After calcination and impregnation,the Ru/TiO₂–mixed metal oxides?MMO?catalysts were obtained and applied to CO selective methanation.The effect of TiO₂ deposition on the morphology,structural,stability and catalytic performance of the catalysts was investigated.It was found that the TiO₂ was mainly present in anatase phase.And the TiO₂ deposition had no great influence on the structure of LDHs,but could contribute to the formation of smaller crystallites size and increased thermal stability of LDHs,which was favourable for the metal dispersion of supported catalysts.As the deposition content of TiO₂ is 15%,the obtained Ru/15TiO₂-MMO catalyst showed larger specific surface area?SSA?and better performance for CO selective metanation,which can remove the CO outlet concentration to below 10 ppm with a selectivity greater than 50%over the wider low–temperature range of 175–260oC.Furthermore,the catalyst also showed high stability with no deactivation during a long–term durability test?120 h?.?3?RuLDHs/CNTs/NF catalyst precursor was fabricated by the deposition of RuLDHs on the CNTs/NF via a facile hydrothermal method.After topotactic transformation,the RuNi/Al₂O₃–CNTs/NF catalyst with high dispersion and stability,and good conductivity was prepared and applied to CO selective methanation.The morphology,composition,structure and stability of RuLDHs/CNTs/NF composites,and the metal dispersion and catalytic performance of RuNi/Al₂O₃–CNTs/NF catalyst were studied systematically.Results showed that the RuLDH nanosheets were uniformly and vertically grown on CNTs.The growth of RuLDH nanosheets not only prevent the aggregation of CNTs,but also create new pores and crevices;the presence of CNTs can help disperse and stabilize the RuLDHs,which contributed to the high dispersion and stability of active metals.The prepared RuNi/Al₂O₃–CNTs/NF catalyst exhibited superior catalytic performance for CO-SMET?i.e.,CO outlet concentration less than 10 ppm and CO-SMET selectivity greater than 50%?over a wide reaction temperature window of 190–250°C.In addition,this catalyst also showed good stability during a long–term durability test?120 h?.?4?Non–noble metal–based Ni/ZrO₂ catalysts were successfully prepared by employing UiO-66 as precursor and template,and NiCl₂·6H₂O as Ni precursor,followed by calcination and reduction.The effect of Ni loading on the size,dispersion,pore structure and catalytic performance of Ni/ZrO₂ was investigated.Results showed that the average size and dispersion of Ni metals were 3.5 nm and 15.3%,respectively,and the ZrO₂ support was mainly present in tetragonal phase.When the Ni loading is 13%,the Ni/ZrO₂ catalyst showed the larger SSA and better catalytic performance for CO selective methanation,which can deep–remove CO outlet concentration to below 10 ppm with selectivity greater than 50%over a wider reaction temperature window of 215–350°C.Furthermore,this catalyst had good stability,showing CO and CH₄outlet concentrations of about 1×10^-6 and 1%during a long–term stability test?120 h?.