4.2. Mechanism of the improved catalytic reactivity of Pt/Ni nanoalloys
According to the classic Langmuir–Hinshelwood model [40], the reduction of PNP by borohydride over a metal catalyst occurs after both reactants are adsorbed onto the metal surface. Although the transformation of PNP to PAP is a multi-step reaction, the rate limiting step is the adsorption of PNP under the alkaline condition with excess borohydride [61]. The potential for an inadequate adsorption of View the MathML source is not of concern because borohydride is always in excess. As shown in Fig. 4d, two exponential functions are found on both sides of the optimal Pt/Ni composition (i.e., θ = 44%), revealing the limiting conditions with overly strong PNP adsorptions by Pt on the left and by Ni on the right [62].