Characterization: The samples of, G-Pt, G-Pd, G-PdPt (No PVP) and G-PdPt (with PVP) were characterized with X-ray diffraction (XRD, Brukers D8 focus X-ray diffractometer), transmission electron microscope (TEM, FEI Tecnai G2 U-twin instrument with accelerating voltage of 200 kV, FEI TITAN with accelerating voltage of 300 kV), Raman (WITec GmbH alpha 300R Raman spectrometer) and UV-Visible (Jasco V-670 UV-vis spectrophotometer) spectrophotometers. The chemical and electronic states of Pt and Pd present in G-PdPt (No PVP) and G-PdPt (with PVP) hybrids were determined using X-ray photoelectron spectroscopy (XPS). The XPS measurement were performed on a PHI 5000 Versaprobe II , Focused X-ray photoelectron spectrophotometer, FEI, with monochromatized Al k? X-ray source (1486.6 eV photons) at a pressure of 3 x 10-10 Torr. The XPS measurements were typically recorded within a range of 0-1100 eV. The peak position or the binding energies were referenced or calibrated to the C1s peak at 284.6 eV to nullify any effect of surface charging. The formation of PdPt alloy on graphene was also probed by obtaining the in-situ UV-Vis spectra of G-Pd, G-Pt and G-PdPt reaction solutions as a function of time, following the addition of respected reducing agents (sodium citrate; reducing agent for Pd2+ ions and ascorbic acid; reducing agent for Pt2+ ions). It is to be noted that there is no report available about the SPR activity of Pt nanoparticles. However, Pd has been reported to exhibit SPR peak at 368 nm 23. Therefore, any change or variation in the peak position of Pd in the UV-Visible spectra will provide the information about formation of PdPt alloy nanoparticles.
The activity of the hybrids for CO oxidation reaction was measured in a fixed-bed reactor of 5 mm length under atmospheric pressure using 50 mg of catalyst. The gas flow rates were controlled by mass flow controllers (Alicat MC series). The flow rates tested were 30 sccm, 40 sccm and 50 sccm with a temperature range of 30–300° C. The quartz reactor was placed in a tubular furnace and the temperature of the furnace was controlled by a temperature controller (TF 1200 Tempsen) The catalyst bed temperature was measured by a K-type thermocouple. The effluent gases were analyzed online by a gas chromatograph (Mayura Analytical Pvt Ltd Model 1100) equipped with an auto gas sampler with TCD and a FID detector. The activity was examined by looking at the CO conversion using the formula;
% CO conversion= (COinitial-COfinal/ COinitial) X 100
The molecular dynamics simulations were performed with the LAMMPS 36 software package. To describe accurately the Pd and Pt atoms, the EAM force field EAM was utilized 39. The systems considered were two juxtaposed cubes (one Palladium, other Platinum) with 60 ? edges and two spheres with 60 ? of radius. The box was filled with 1000molecules of CO. The interactions of CO molecules, as well as the Lennard-Jones between gas and metal were obtained from reference 40. First an energy minimization was applied on both systems and then a long 15 ns run was made on NVT ensemble at 300 K, using Nose-Hoover thermostat 41, 42. The time step utilized was 1 fs and the acquiring of data was done each 10 ps.