Mild Ammonia Synthesis over Ba-Promoted Ru/MPC Catalysts: Effects of the Ba/Ru Ratio and the Mesoporous Structure

Masayasu Nishi,Shih-Yuan Chen,Hideyuki Takagi

doi:10.3390/catal9050480

Masayasu Nishi, Shih-Yuan Chen + Show 1 more

Open Access

https://doi.org/10.3390/catal9050480

Copy DOI

Abstract

A series of novel mesoporous carbon-supported, Ba-promoted, Ru catalysts with Ba/Ru ratios of 0.1–1.6 and a Ru loading of 10 wt% (denoted as 0.1–1.6Ba-10Ru/MPC) were prepared via stepwise impregnation of Ru and Ba precursors on the mesoporous carbon materials. The catalysts were applied to mild ammonia synthesis and compared to reference materials, including an analog of the prepared catalyst with a Ba/Ru ratio of 1.6 and a Ru loading of 10 wt% (denoted as 1.6Ba-10Ru/AC). Characterization by X-ray diffraction (XRD), nitrogen physisorption, and electronic microscopy revealed that the 0.1–1.6Ba-10Ru/MPC catalysts contained Ru particles (approximately 2 nm) that were well-dispersed on the mesoporous structure and nanostructured Ba(NO3)2 species. These species decomposed into amorphous BaOx species, acting as a promoter on the metallic Ru particles forming catalytically active sites for ammonia synthesis. All the 0.1–1.6Ba-10Ru/MPC catalysts showed a synergistic effect of the active Ba and Ru species, which were stabilized in the mesoporous carbon framework with fast molecular diffusion and could effectively catalyze mild ammonia synthesis (280–450 °C and 0.99 MPa) even under intermittently variable conditions, particularly for those with Ba/Ru ratios of >0.5. In contrast, the 1.6Ba-10Ru/AC analog showed poor activity and stability for ammonia synthesis due to the sintering of Ba and Ru particles on the outer surface of the microporous carbon framework, resulting in low molecular diffusion and weak synergistic effect of the catalytically active sites.

Highlights

Introduction80% of national CO2 emissions by 2030 and 2050, respectively, based on the data recorded in
The atmospheric CO2 concentration has rapidly increased over the past two decades due to the burning of fossil fuels, causing increases in global temperature, sea level, and extreme climate [1].As part of the adoption of the Paris Agreement, the Japanese government has set a goal to cut 26%and 80% of national CO2 emissions by 2030 and 2050, respectively, based on the data recorded in2013 [2]
We developed a series of novel mesoporous carbon-supported and Ba-promoted Ru catalysts for mild ammonia synthesis compared to several reference catalysts

Summary

Introduction

80% of national CO2 emissions by 2030 and 2050, respectively, based on the data recorded in. To achieve this goal, hydrogen is a promising energy source with clean emissions, for hydrogen produced by water electrolysis using renewable energy [3]. Hydrogen is flammable, expensive, and hard to liquify, rendering its storage, transportation, and utilization quite difficult. The conversion of hydrogen to various chemicals, so-called “hydrogen carriers”, is a potential method to store, transport, and use hydrogen energy more safely [4]. Ammonia (NH3 ) is composed of one nitrogen and three hydrogen atoms, corresponding to 17.6 wt% hydrogen and its industry is experienced including well-developed infrastructure for production, transportation, storage, Catalysts 2019, 9, 480; doi:10.3390/catal9050480 www.mdpi.com/journal/catalysts

Methods

Results

Conclusion