Highly Efficient Hierarchical Porous Carbon Supported Pd-Based Catalysts for Additive-Free Dehydrogenation of Formic Acid

Xinyi Miao,Xiaohui Ji,Xianzhao Shao,Wei Wang,Fengwu Tian,Yujia Zhang,Miaomiao Bai,Zuoping Zhao

doi:10.3390/catal12020240

Abstract

Formic acid (FA) is one of the most prospective hydrogen carriers for renewable energy transformation. In this context, the addition of extra-amine is always required for promoting the reactivity of FA, which is still a key challenge. Herein, we report a simple but effective strategy to synthesize Pd nanoparticles, supported on NH2-functionalized, phosphorous-doped glucose-based porous carbon (NH2-P-GC). The introduction of NH2- groups on the support acts as an immobilized amine-additive for FA dehydrogenation, while phosphorus not only serves as an electronic promoter to keep Pd in the electronic deficient state for FA dehydrogenation, but also as an enlarger of the aperture size of the carbon. As a result, the Pd/NH2-P-GC has exceptional catalytic activity, 100% H2 selectivity, CO generation that is undetectable, and good reusability for hydrogen production from FA. In the additive-free dehydrogenation of aqueous FA solution, the initial turnover frequency (TOF) can reach 5126 h−1 at room temperature, which is substantially higher than the best heterogeneous catalyst so far recorded. Overall, the system’s high activity, selectivity, stability, and simplicity in producing CO-free H2/CO2 gas from FA, without the need for any additive, makes it attractive for practical deployment.

Highlights

Increased CO2 emissions due to the ever-increasing consumption of fossil fuels have led to global warming, affecting human beings with serious consequences [1,2,3]
The turnover frequency (TOF) value was computed on the basis of the total number of Pd atoms supplemented into the reaction system, and is calculated from the following equation: Xα
Patm Vgas / RT 2nmetal t where Xα is the conversion rate; Vgas is the volume of the gas (H2 + CO2) produced by the reaction; Patm is the atmospheric pressure (101,325 Pa); T is the room temperature (298 K); R is the universal gas constant (8.3145 m3·Pa·mol−1·K−1); nFA is the number of moles of formic acid; TOFinitial represents the initial conversion frequency (h−1) when Xα reaches

Summary

Introduction

Increased CO2 emissions due to the ever-increasing consumption of fossil fuels have led to global warming, affecting human beings with serious consequences [1,2,3]. In view of this, replacing fossil fuels with sustainable energy sources is a prerequisite [4]. Efficient hydrogen storage is a challenge, as a result of low critical temperature and a small value of volumetric energy density [7]. In this regard, chemical hydrogen storage has been widely studied [8,9]. As one of the most prospective hydrogen carriers, formic acid (FA) has a high energy density (53 g L−1, 1.77 kW L−1) [10,11], is non-toxic, and is convenient to use [12,13,14]. It is imperative to find suitable catalysts with high activity under a mild condition, for selective dehydrogenation of FA, to produce ultrapure H2 for subsequent utilization in the fuel cells

Methods

Results

Conclusion