Preparation Of Pd Catalysts By Solution Method And Their Catalytic Behaviour Towards Hexavalent Chromium In Water

The frequent occurrence of chromium pollution incidents caused by the rapid development of industry has attracted more and more public attention and attention.Cr（Ⅵ）has strong migration ability in the aquatic environment,is a highly toxic and carcinogenic substance,and has been identified internationally as one of the highest priority toxic pollutants,and Cr（Ⅲ）is much less toxic than Cr（Ⅵ）,so reducing Cr（Ⅵ）to Cr（Ⅲ）with an effective method has become an effective way to deal with chromium pollution.In the presence and action of the Pd catalyst,the reducing agent formic acid can efficiently reduce Cr（Ⅵ）to Cr（Ⅲ）,and the product is only pollution-free.Although the Pd colloidal catalyst also has a high catalytic reduction activity,due to the difficulty of recovery of Pd colloid after use,the price of precious metal Pd is too high,so the preparation of a supported Pd catalyst can effectively solve this problem.In this paper,Pd nanoparticles assisted by different surfactants were prepared by a simple method,and the payload was successfully carried out to obtain the Pd/Al₂O₃supported nanocatalyst.By changing the loading rate of Pd in the preparation process,the amount of surfactant used,the reaction time,the reaction temperature,and the use of the effective removal of excessively used surfactant method,and as a catalyst for the Cr（Ⅵ）catalytic reduction reaction with formic acid as the reducing agent,the influence of catalyst preparation conditions on the catalyst reduction efficiency was explored,and the research content included the following two points:（1）Pd nanoparticles prepared with polyvinylpyrrolidone（PVP）as a protective agent.The dispersion on the support was good,and no agglomeration phenomenon was generated,which was characterized by ICP,XRD,TEM,XPS and other analytical means,and the effect of Pd/Al₂O₃nanocatalyst preparation conditions on the catalyst reduction efficiency was explored in the experiment of formic acid catalytic reduction degradation of Cr（Ⅵ）.When the activity test conditions were at room temperature,p H=3.6,the amount of catalyst was 8 mg,and the initial concentration was 0.1 mg/m L,the Pd/Al₂O₃nanocatalyst prepared at the theoretical load rate of 2 wt%,n（PVP/Pd）=4.8,180℃reaction for 12 h showed high catalytic activity for catalytic reduction degradation of Cr（Ⅵ）.（2）Pd nanoparticles prepared with cetyltrimethylammonium bromide（CTAB）as a protective agent have a regular concave cube morphological structure,and there are many fissures inside it.The effect of Pd/Al₂O₃nanocatalyst preparation conditions on catalyst reduction efficiency was investigated in the experiment of catalytic reduction degradation of Cr（Ⅵ）by ICP,XRD,TEM,XPS and other analytical methods.When the activity test conditions were at room temperature,p H=3.6,the amount of catalyst was 8 mg,the initial concentration was 0.1 mg/m L,the Pd/Al₂O₃nanocatalyst obtained at the theoretical loading rate of 5 wt%,the amount of CTAB was n(Pd²⁺)/n（CTAB）=1:1,the reaction time was 5 min,and the reaction temperature was 60℃,the Pd/Al₂O₃nanocatalyst showed a high catalytic activity for catalytic reduction degradation of Cr（Ⅵ）.The"deposition-redistribution"method was used to deeply treat the excess CTAB,and the experiment showed that this method can achieve more thorough and effective depth treatment of the overused surfactant,which was fully verified in the catalytic reduction degradation of Cr（Ⅵ）.