Ultrafine PtCo Alloy Nanoclusters Confined in N-Doped Mesoporous Carbon Spheres for Efficient Ammonia Borane Hydrolysis

Abstract

Developing cost-effective and high-efficiency catalysts for efficient ammonia borane (AB) hydrolysis is highly desirable but remains a great challenge. Ultrafine catalysts are attractive candidates in catalysis owing to abundant surface atoms. Herein, a series of ultrafine Pt x Co1–x alloy nanoclusters with an average size of 1.6 nm are homogeneously anchored within the mesoporous channels of N-doped mesoporous carbon spheres (N-MCSs) through an enhanced strong electrostatic adsorption (SEA) strategy. The ultrafine PtCo nanoclusters confined in N-MCSs lead to superior catalytic performance toward the AB hydrolysis reaction. Particularly, the optimal Pt0.33Co0.67/N-MCSs catalyst exhibits excellent performance toward the AB hydrolysis reaction. The results reveal that the highest specific rate achieves 4902 molH2 molPt –1 min–1, which is approximately 18 times higher than that of the monometallic Pt/N-MCSs catalyst. Mechanistic studies adopting kinetic isotope effects demonstrate that the O–H cleavage of H2O molecules is the rate-determine step in the AB hydrolysis reaction. Inspired by the above results, a possible reaction mechanism is proposed, which will give a new viewpoint for the rational design of cost-effective catalysts for AB hydrolysis.

Intrinsic size‐dependent activity of Pt nanoparticles without masking by heterogeneous oxidation states of Pt for hydrolytic dehydrogenation of NH 3 BH 3

“…[10][11][12] In this respect, it has been required to reveal the intrinsic sizedependent activity of catalytic nanoparticles for efficient hydrolytic dehydrogenation of AB, and thus the sizedependent catalytic activity of nanoparticles has been addressed in the nanometric regime and sometimes even in subnanometric one. [13][14][15] Nevertheless, in many cases, the apparent catalytic activity of nanoparticles could be affected not only by the intrinsic particle size effect but also by additional effects such as the nanoparticlesupport interaction and the heterogeneous oxidation states of nanoparticles. 4,[16][17][18] Various catalysts have been suggested for the hydrolytic dehydrogenation of AB, 7,13,14 and Pt catalysts are considered to be superior among the catalysts.…”

“…[13][14][15] Nevertheless, in many cases, the apparent catalytic activity of nanoparticles could be affected not only by the intrinsic particle size effect but also by additional effects such as the nanoparticlesupport interaction and the heterogeneous oxidation states of nanoparticles. 4,[16][17][18] Various catalysts have been suggested for the hydrolytic dehydrogenation of AB, 7,13,14 and Pt catalysts are considered to be superior among the catalysts. 15,19,20 For example, significantly enhanced hydrolysis of AB compared with other catalysts was demonstrated using Pt nanoparticles confined inside the pores of a metalorganic frame work (MOF, specifically MIL-101; Pt@MIL-101), Pt nanoparticles supported on carbon nanotubes (CNTs; Pt/CNTs), Pt nanoparticles decorated on three-dimensional (3D) nanoporous TiO 2 (3D Pt@TiO 2 ), and poly(N-vinyl-2-pyrrolidone; PVP)-protected Pt nanoparticles on modified SiO 2 .…”

“…In particular, the hydrolytic dehydrogenation of ammonia borane (AB, NH 3 BH 3 ) has been of interest as an emerging means of hydrogen production due to intrinsic advantages of AB such as stability, nontoxicity, and high hydrogen density and selectivity for practical applications 10‐12 . In this respect, it has been required to reveal the intrinsic size‐dependent activity of catalytic nanoparticles for efficient hydrolytic dehydrogenation of AB, and thus the size‐dependent catalytic activity of nanoparticles has been addressed in the nanometric regime and sometimes even in subnanometric one 13‐15 . Nevertheless, in many cases, the apparent catalytic activity of nanoparticles could be affected not only by the intrinsic particle size effect but also by additional effects such as the nanoparticle‐support interaction and the heterogeneous oxidation states of nanoparticles 4,16‐18 …”

“…Various catalysts have been suggested for the hydrolytic dehydrogenation of AB, 7,13,14 and Pt catalysts are considered to be superior among the catalysts 15,19,20 . For example, significantly enhanced hydrolysis of AB compared with other catalysts was demonstrated using Pt nanoparticles confined inside the pores of a metal‐organic frame work (MOF, specifically MIL‐101; Pt@MIL‐101), Pt nanoparticles supported on carbon nanotubes (CNTs; Pt/CNTs), Pt nanoparticles decorated on three‐dimensional (3D) nanoporous TiO 2 (3D Pt@TiO 2 ), and poly(N‐vinyl‐2‐pyrrolidone; PVP)‐protected Pt nanoparticles on modified SiO 2 21‐26 .…”

Heteroatom Modified Polymer Immobilized Ionic Liquid Stabilized Ruthenium Nanoparticles: Efficient Catalysts for the Hydrolytic Evolution of Hydrogen from Sodium Borohydride*

“…While the high activity obtained with small nanoparticles is due to their high surface area to volume ratio and the large number of active sites, they are unstable with respect to aggregation to less reactive species which limits their practical applications [44][45], for example, integration into hydrogen-based fuel cells for use in vehicles and portable electronic devices [46][47][48]. One potential solution to overcome aggregation under conditions of catalysis has been to stabilise the nanoparticles by encapsulation into a support such as porous carbon structures [49][50][51][52][53][54][55][56][57][58][59][60], zeolites [61][62][63][64][65], mesoporous silicas [66][67][68], porous organic polymers [69][70], metal organic frameworks [71][72][73][74][75][76][77] and, most recently, dendrimers [78][79][80]. Additional benefits of this strategy include control of the growth and morphology due to the confinement [81][82][83][84][85][86]…”