Study On The Preparation And Performance Of Inorganic Hydrophobic Platinum Catalyst

The hydrogen isotope exchange reaction between hydrogen and water using hydrophobic catalysts is an effective method in water detritiation due to its mild operating conditions.An effective hydrophobic catalyst with stability and high activity is very important to hydrogen isotope exchange reaction.A new kind of inorganic Pt hydrophobic catalyst supported on hydrophobic nickel was successfully prepared in this paper.Hydrophobic surfaces were successfully fabricated on pure nickel substrates by a one-step chemical etching process with different acidic solutions.Pt and Pt/C nanoparticles with small size and highly dispersed were synthesized by solvothermal synthesis using ethylene glycol as reducing agent and dispersant,carbon as dispersing carrier.The inorganic Pt hydrophobic catalysts were prepared by directly coating hydrophobic nickel sheets after chemical plating with Pt/C catalysts.The catalytic activity of inorganic Pt hydrophobic catalyst was examined by H2-HDO catalytic exchange reaction.The structured hydrophobic surfaces were fabricated on nickel substrates by chemical etching with acid etchants.After chemical etching,terrace-like,crater-like and spike-like microstructures were observed on the surfaces.The irregular microstructures formed after etching would significantly enhance the surface roughness,and the wettability of Ni surface changed from hydrophilic to hydrophobic.The examination of surface chemical compositions implied that there were almost no polar moieties which can enhance the surface hydrophobicity on the surface after chemical etching,except part of the surface was oxidized.After etching by 10.2 wt%HC1 or 10.1 wt%H2SO4 for 42 h,the values of surface roughness Ra were bigger than 6.0 ?m,and the contact angle on the etched surface could reach more than 140°,showing excellent hydrophobicity.The wettability of nickel surface after etching could be analyzed by Cassie-Baxter equation.This unique surface texture formed after etching contributed to trapping large amounts of air,which can prevent the liquids contacting the nickel substrate.As the proportion of liquid-gas interface in the composite surface increases,the surface contact angle increases,and the surface becomes hydrophobic.Pt nanoparticles were synthesized by solvothermal synthesis using ethylene glycol as reductant and dispersant under uniform high temperature condition.When the content of chloroplatinic acid in the reaction system was 0.01 mmol,the amount of ethylene glycol and water was 12 mL and 0.5 mL,respectively.The Pt nanoparticles were synthesized after reaction at 180? for 30 min,and the average particle size,dispersity and specific surface area of Pt nanoparticles were 1.06 nm,1.02 nm-1 and 2.64×105 m2/g,respectively.The average size of Pt nanoparticles prepared by this method is smaller than those reported in literature.Pt/C catalysts were also synthesized by solvothermal synthesis using carbon as dispersing carrier,ethylene glycol as reductant and dispersant.When the content of chloroplatinic acid was 0.01 mmol,the amount of ethylene glycol was 13 mL,the weight of carbon was 5.85 mg,the 25 wt%Pt/C catalyst was synthesized after reaction at 180? for 30 min.The average particle size,dispersity and specific surface area of Pt/C catalysts were 1.03 nm,1.05 nm-1 and 2.72×105 m2/g,respectively.The Pt/C catalysts were completely deoxidized after heat treatment with H2/N2 mixed gases at 400? for 1.5 h.The Pt/C catalysts have high catalytic activity because of the increase of Pt0 content.Pt in the Pt/C catalyst was almost consisted by Pt0 after reduction,and the average particle size of Pt increased to 1.71 nm.The foam nickel was used as the hydrophilic filler,and the hydrophobic nickel sheets were employed as support carrier.Pt particles were formed on the foam nickel and hydrophobic nickel sheet after chemical plating by chloroplatinic acid.Then the inorganic Pt hydrophobic catalysts were prepared by directly coating hydrophobic nickel sheets with Pt/C catalysts.After heat treatment with H2/N2 mixed gases at 400? for 1.5 h,Pt on the nickel surface entered into the nickel matrix,resulting in the change of lattice constants of each other and increasing the binding force between active component Pt and the matrix.With the removal of residues in Pt/C catalysts,the nanoparticles on the catalyst surface became dense,the sizes and distributions of nanoparticles tended to be uniform.The Pt in the catalysts was almost composed of Pt0.During the H2-HDO isotope exchange reaction,H2 was adsorbed and dissociated into H(ads)and H(ads)on the Pt surface,occupying the adsorption site.Water vapor molecules of HDO was not dissociated on the Pt surface,but interacted with H(ads)to form hydrated ions H(HDO)n+(ads).Then H and D exchanged forming D(H20)(HDO)n-1+(ads),which can convert into water vapor molecules and D(ads).D(ads)and H(ads)on the Pt surface were combined to form HD molecule.At last,H2O and HD molecules were desorbed from Pt surface.The H2-HDO isotope catalytic exchange reaction was carried out at 70? by using foam nickel and inorganic Pt hydrophobic catalysts with the contact angles more than 120°.The reaction rate was rapid at the beginning,a mass of D transferred from the water to the gas.The content of D in the water decreased and the content of D in the gas increased.When the gas-liquid ratio was 1.2,after reaction for 15 min,the column efficiency ? and the mass transfer coefficient Kya was 67.96%and 0.25 m3·s-1·m-3,respectively.Compared with the Pt hydrophobic catalysts prepared by similar methods,the preparation method adopted in this paper is simple,easy to operate,need fewer raw materials and can bring less loss and less waste of Pt.The inorganic Pt hydrophobic catalysts have very high activity with the Pt particles of small size,high content of Pt0 and high utilization.The inorganic Pt hydrophobic catalysts can obtain good catalytic exchange performance at low load of Pt.As mentioned above,this paper provided a new method for preparing inorganic hydrophobic carrier,and developed a new method to synthesize Pt nanoparticles and Pt/C catalyst with small size and highly dispersed.A new kind of inorganic Pt hydrophobic catalyst was successfully prepared.The binding force between active component Pt and the matrix was increased and the catalytic effect of inorganic Pt hydrophobic catalyst was improved by chemical plating Pt on the surface of nickel.