Research For Chlorophenols Removal On Supported Pd-M Catalysts

With the rapid development of industry and agriculture, the pollution of water resources is increasingly serious, among which the chlorophenol organic compounds is a large class of hazards substances in water environment. Human beings were harmed directly or indirectly by chlorophenol organic compounds. The catalytic reduction method has the advantages of economic, efficient and low energy consumption, no pollution, etc. on the removal of chlorophenols compounds. The technologyis veryworthyofstudy.In this paper, we prepared a series of Pd-In/gamma-Al2O3, Pd-Cu/AC bimetallic catalysts and Pd-In-Cu/gamma alumina trimetallic catalysts with different In/Pd or Cu/Pd mole ratio with Pd loading amount to 1% in all the catalysts using the step by step impregnation method and co-impregnation method for hydrodechlorination of chlorophenols. We characterized the crystal structure, surface morphology, particle shape, particle size and dispersion degree as well as surface area of the Pd, In and Cu metal particles of the catalysts by X-ray diffraction(XRD), scanning electron microscopy(SEM)- dispersive X-ray spectroscopy(SEM-EDS), high resolution transmission electron microscope(HR-TEM), X-ray electron energy spectrum(XPS), temperature programmed reduction(TPR), H2 pulse chemisorption determination method of characterization methods. The reaction was carried out in a glass reactor by adding the water solution of chlorophenols and catalyst with the H2 bubbling, and the products were analyzed by gas chromatography. The effects of preparation methods, and the Pd-M molar ratios as well as carrier of catalysts onthecatalytic activityandselectivitywereinvestigated.The experimental results shows that the Pd and In, Pd and Cu metalparticles of Pd-In bimetallic catalysts and Pd-Cu bimetallic catalysts are mainly distributed on the surface of the supports. In the Pd-In/γ- Al2O3 catalyst, the Pd particle size was mainly distributed in 2nm-5nm. With indium/palladium molar ratio increasing, the catalytic performance of the catalysts increased first and then decreased mainly because of adding an appropriate amount of In that can improve the metal palladium dispersion and surface area of the catalysts. The palladium dispersion and surface area of CP-2 catalyst is the largest, reaching 41.6% and 92.7 m2g-1 respectively, while pure palladium catalyst is 23.7%and 52.9 m2g-1.As the indium content gradually increased, the catalyst will generate indium palladium alloys which inhibits the conversion of 4-chlorophenol. The Pd particle size wasmainly distributed in 1nm-6nm in Pd-Cu / AC bimetallic catalysts. The catalytic performance of the catalyst increased first and then decreased with copper palladium molar ratio increasing. The main reason is copper content changes in the copper palladium bimetallic catalyst. When the content lower of copper, the copper particles dispersed in the palladium particles and increased the degree of catalysts’ dispersion and surface area, while with the increasing of copper content more than a certain value the copper particles began covering the palladium particles surface or with palladium particle form alloy so as to reduce the catalyst activity in the catalyst. The dispersion and surface area of palladium in CP-2 catalyst is the largest, reached 47.6% and 106.2 m2g-1 respectively. The activity of CP-2 catalyst is also confirmed the best which be able to transform 4-chlorophenol within 30 minutes completely. Compared with the copper-palladium bimetallic catalyst loaded on the alumina,the copper-palladium bimetallic catalyst loaded on the active carbon has higher catalytic activity mainly because the surface area of the activated carbon was significantly higher than that of the alumina surface area(activated carbon surface area is 704 m2g-1, and the surface area of the alumina is 92.3 m2g-1), therefore using activated carbon as catalyst carrier than with alumina as carrier of catalyst has higher dispersion of palladium. On the other hand, because of no metallic components exist in the activated carbon, the interaction between the active center of palladium with carrier is relatively weak when activated carbon as a carrier. On the contrary, the interaction between alumina with palladium is larger, so the catalysts shows the higher catalytic activity using activated carbon as catalyst carrier. The CP-2 catalyst supported on activated carbon will be able to complete the conversion of chlorophenol in half an hour, while the CP-1-2 catalyst with alumina as the carrier neededanhour.The catalysts IP-2 with molar ratio of In/Pd 0.1/1 and prepared by first In and Pd impregnated exhibit optimal performance for the catalytic removal of chlorophenol. Among the Cu-Pd catalysts supported on activated carbon, the catalyst CP-2 with Cu / Pd molar ratio is 0.3/1 and prepared by first Cu and then Pd impregnation has optimum performance for removal of chlorophenol. The above results showed that the conversion rate of chlorophenol is mainly related to the degree of dispersion and specific surface of Pd, the higher degree dispersion of the catalyst can improve the catalytic activityofthe catalyst.The catalytic activity for hydrogenation of 4-chlorophenol removal of supported copper,palladiumandindiumtrimetallic catalysts wereverylowerthan thecatalytic activityofthebimetalliccatalyst. The catalytic activity of trimetallic catalysts made by mixed impregnated three metal of indium, palladium and copper is higher than the catalysts made by first indium then palladium copper. The catalytic performance of catalysts prepared by first copper then palladium indium impregnation sequence is superior to that of first indium then palladium copper series trimetallic catalyst.