Modulating Co-Re Pairs in CoRe Alloy for Efficient NH₃ Synthesis under Mild Conditions.

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Efficient ammonia (NH3) synthesis is vital for agriculture and industry.
• Nonprecious-metal (NPM) catalysts are sought as alternatives to traditional precious metals.
• Monometallic catalysts face challenges with N2 activation and NH3 desorption.

Purpose of the Study:

• To develop advanced NPM catalysts for efficient ammonia synthesis under mild conditions.
• To investigate the effect of Cobalt-Rhenium (CoRe) alloy composition on catalytic performance.
• To understand the structure-activity relationship in CoRe catalysts for ammonia synthesis.

Main Methods:

• Systematic fabrication of CoRe_x alloy catalysts with varying Co/Re ratios (x = 0.25, 0.5, 0.75, 1, 1.5, 2).
• Evaluation of catalytic activity for ammonia synthesis under specific temperature and pressure conditions.
• Analysis of the correlation between Co-Re paired sites and catalytic performance.

Main Results:

• The Co/Re ratio critically influences the formation of Co-Re paired sites.
• Optimal NH3 synthesis rates were observed with CoRe1, attributed to abundant Co-Re pairs.
• Excessive Co or Re in the alloy negatively impacted N2 activation or NH3 desorption.
• CoRe1 exhibited a high ammonia synthesis rate of 12.0 mmol gcat-1 h-1 at 400 °C and 1 MPa.

Conclusions:

• CoRe alloy catalysts, particularly CoRe1, demonstrate significant potential for efficient ammonia synthesis.
• The synergistic effect of Co-Re orbital hybridization in CoRe1 facilitates both N2 activation and NH3 desorption.
• Optimized CoRe alloys outperform many previously reported NPM catalysts for ammonia synthesis.