How can Pt/C or Ni/C both as a metal and supporting material respectively be impregnated so that they can be used as a catalyst?
[A]The process of formation of modified catalysts involves deposition of Pt and Ni particles on activated carbon, using a poly-acrylate anchor.
[B] Modified catalysts are ,in a way, are nano sized doped substances.Depending upon the extent of doping and conditions of doping, there will be a change in the porocity [size/ shape/ number of pores] in whole of the metal bulk accompanied by presence of more number of free valencies on the surface and change[ generally decrease] in the lattice constants. All these factors would favor adsorption[ physical/ chemical] of the foreign substance all the more and, thereby, enhance the catalytic activity; of course, keeping their selectivity intact.
[C] Although, Ni/C works much better than Ni or finely divided Ni, yet the concept of modified catalyst is better explained and therby better utilized in case of the noble metals[Pt/C] because:
[I] Noble metals are not at all susceptible to oxidation by atmospheric O2 while other reactive metal MAY become susceptible.
[II] Noble metals can be dispersed into nano scale particles much more easily than most of other transition metals which can easily adsorb H2/O2.
[III] Porocity of Pd or Pt is much more amenable toH2 adsorption.
[IV].The electrons present in the filled d-subshell (being more exposed) make dissociative adsorption of H2/O2 some what easier.
[V] It is very easy to prepare a MODIFIED CATALYST out of the noble Pd and Pt by impregnating the metal surface with carbon, silica and alumina which can make the reactions to occur at much softer reaction conditions that those of unmodified Pd and Pt catalysts.
For example, hydrogenation of 2,4-DNT to 2,4 DAT occurs at 5Mpa /150C in MeOH solvent with Ni; with Pd/C modified catalyst( called carbon supported Pd), the reaction proceeds at 0.4Mpa/ 90C but without MeOH solvent while with Pd/Al2O3 modified catalyst(called alumina supported Pd) occurs at 0.5-0.4Mpa/72C without MeOH.
[VI] Lastly, in case of supported catalysts, the oxidation/coupling/hydration/reduction reactions can take place under ambient conditions very efficiently and cost effective because a very small amount of noble metal dispersed on solid support can give a very high re-activity.
Here attached is a paper about Pd deposition onto carbon. For depositing Pt, just use exactly the same protocol with H2PtCl6 instead of H2PdCl4. For Ni, you can impregnate your carbon material with a concentrated solution of nickel nitrate, then dry and pyrolyse it at 900°C. At such temperature, NiO coming from the thermal decomposition of the nickel salt, will be reduced into metal Ni by simple contact with carbon, leaving Ni nanoparticles at the carbon surface.
Alain
Prepare concentrated solution of respective nickel salt as nitrate and Platinum as H2PtCl6. Imperiginatethese with active carbon material and pyrolyse at high temp.
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