The Haber Process Made Efficient by Hydroxylated Graphene

TL;DR

This paper introduces hydroxylated graphene as a catalyst modifier that significantly enhances ammonia production in the Haber-Bosch process by shifting the reaction equilibrium towards ammonia, reducing energy requirements and costs.

Contribution

The study demonstrates a novel use of hydroxylated graphene to improve Haber-Bosch efficiency, supported by electronic structure calculations and reactive simulations.

Findings

Approximately 50 kJ mol-1 enthalpy gain at 298-1300 K

Approximately 60-70 kJ mol-1 free energy gain at 1-1000 bar

Significant increase in ammonia yield with reduced temperature and pressure

Abstract

The Haber-Bosch process is the main industrial method for producing ammonia from diatomic nitrogen and hydrogen. Very demanding energetically, it uses an iron catalyst, and requires high temperature and pressure. Any improvement of the Haber process will have an extreme scientific and economic impact. We report a significant increase of ammonia production using hydroxylated graphene. Exploiting the polarity difference between N2/H2 and NH3, as well as the universal proton acceptor behavior of NH3, we demonstrate a strong shift of the equilibrium of the Haber-Bosch process towards ammonia. Hydroxylated graphene provides the polar environment favoring the forward reaction, and remain stable under the investigated thermodynamic conditions. Ca. 50 kJ mol-1 enthalpy gain and ca. 60-70 kJ mol-1 free energy gain are achieved at 298-1300 K and 1-1000 bar, strongly shifting the reaction equilibrium towards the product. A clear microscopic interpretation of the observed phenomenon is given using electronic structure calculations and real-time reactive simulations. The demonstrated principle can be applied with many polar groups functionalizing a substrate with a high surface area, provided that the system is chemically inert to H2, N2 and NH3. The modified Haber-Bosch process is of significant importance to the chemical industry, since it provides a substantial increase of the reaction yield while decreasing the temperature and pressure, thereby, reducing the cost.