Study On PdCu Catalyst Redispersing/Self-Dispersing In Chlorofluorocarbons

The main reason for deactivation of catalysts is the sintering of noble metal catalysts into large particles.With the deactivation of catalyst,the demand for regeneration/recovery of deactivated catalyst becomes more and more obvious.The general recovery plan is to separate the precious metal from the carrier,and then recover the precious metal to prepare a new precious metal catalyst,but this method is time-consuming and laborious and may cause a lot of environmental pollution in the process.It is urgent to find an economical,convenient and green solution.The redispersion of noble metals and sintering are considered to be two aspects of the same process.The redispersion can restore the activity potential of the deactivated catalyst,and the activity of the catalyst can even exceed that of the fresh catalyst.It will be a very economical scheme to use the redispersing phenomenon of precious metals as the catalyst for regenerating and sintering deactivation.However,the effect of precious metal re-dispersion depends on factors such as re-dispersion atmosphere,temperature and time.Several redispersing schemes commonly used at present require strong oxidizing atmosphere and high temperature conditions,which limit their wide application.If the deactivated catalyst is regenerated in situ through a gentler CFCs atmosphere,the energy consumption will be greatly reduced and great economic benefits will be generated.This paper studies deeply on in CCl₂FCClF₂/H₂ atmosphere,Cu,Pd catalyst and redispersion of PdCu alloy catalyst effect.Finding that single-component Cu,Pd catalyst does not redispersion in the atmosphere but PdCu alloy particle dispersion successful from 3.9 nm and 16.6 nm scattered by DFT theory calculation in combination with TEM,XRD,XPS characterization methods.When Cu and Pd form PdCu alloy,the energy barrier of C-Cl bond dissociation on the surface of CCl₂FCClF₂ can be reduced,so that the PdCu alloy can be oxidized by CCl₂FCClF₂,and PdCuCl_y intermediate can be formed on the carrier surface,which can be redistributed to achieve re-dispersion.PdCu alloy particles with different Pd and Cu ratios were treated with CCl₂FCClF₂/H₂ atmosphere.It was found that by adjusting the ratio of Pd and Cu precursors,only PdCu alloy particles with a ratio ranging from 1:0.5 to 1:5 could be formed.Due to the different degree of oxidation of different proportion alloys in the atmosphere of CCl₂FCClF₂/H₂,the re-dispersion effect is different.When the molar ratio of palladium and copper is 1:0.5 and 1:4,the re-dispersion effect is obvious.PdCu alloy catalyst was treated with CFCs atmosphere with different dissociation energy of C-X bond It was found that under the same conditions,the redispersion of PdCu alloy particles increased with the decrease of the dissociation energy of C-Cl bond in the treatment of CFCS,and the redistribution could not occur when the C-X bond in CFCS was difficult to dissociate.The effects of different carriers on the redistribution of PdCu particles were investigated.It was found that the dispersion effect of PdCu on activated carbon carrier was better than that of PdCu on CB carrier under the same conditions,and the redistribution could not occur if Pd and Cu metals did not have direct contact.