Size-controlled PtNi nanoparticles as highly efficient catalyst for hydrodechlorination reactions

Abstract

The application of size-controlled PtNi nanoparticles (NPs) as catalyst on the aqueous-phase hydrodechlorination (HDC) of 4-chlorophenol (4-CP) under ambient conditions (25°C, 1atm) has been investigated. NPs were synthesized as a co-reduction of both metals following a solvothermal method which allowed a proper control of the PtNi alloyed NP size in the range of 4.4–12.0nm. To make the active sites of the nanoalloy accessible, the stabilizer poly(N-vinyl-2-pyrrolidone) was removed by washing of the NPs with H2O2/H2SO4. Evaluating the NP structure/composition influence on the activity, a clear synergic effect between Pt and Ni was found. In this sense, complete conversion of 4-CP was achieved in 1h reaction time with the bimetallic NPs whereas only 70% was reached with the monometallic Pt counterpart (NP size=12nm, [Pt]=80mgL−1, [4-CP]0=78μmolL−1). That effect could be related to the higher resistance of PtNi nanoalloy against chlorine poisoning compared to the monometallic Pt. In fact, PtNi NPs showed a remarkable stability and negligible deactivation even after storing the catalyst one month in the reaction mixture, whereas for the monometallic Pt fully deactivation resulted. The structure-sensitivity of HDC with PtNi nanocatalysts was finally confirmed as the catalytic performance was clearly dependent on the size. A volcano plot like behaviour was obtained, being 5.5nm the optimum size. PtNi-5.5 led to the complete conversion of 4-CP in 15min at a HDC rate of 3.12Lmin−1gPt−1.