Development of catalysts for ammonia synthesis based on metal phthalocyanine materials

Abstract

Highly efficient and very stable iron and/or cobalt-based catalysts for the ammonia synthesis reaction were synthesized by one-step pyrolysis of metal phthalocyanine precursors.

Active and stable Fe-based catalyst, mechanism, and key role of alkali promoters in ammonia synthesis

“…Moreover, in the present work, we performed the activation energy for the FePc catalysts at 6 MPa, which is giving comparably lower activation energy as compared to our previous catalysts performed at 1 MPa. [30] The Lower the value of activation energy itself suggests that there is a facile activation of N 2 on the catalysts surface and preferentially hydrogenated without undergoing direct dissociation on the active site of the Fe catalyst, as demonstrated by DFT calculation. The difference in the catalytic performance between 10-Cs-FePc 700 and 3-K-FePc 700 catalysts (Figure 4 C) could be correlated with the observed apparent activation energies.…”

“…[28,29] Very efficient and stable catalysts for ammonia synthesis have been recently developed in our laboratory based on the pyrolysis of FePc. [30] The same material was also claimed to be precursors for the reverse reaction of ammonia decomposition to H 2 and N 2 . [31] In general, the solid-state pyrolysis of metal-organic compounds (e.g., MOFs or phthalocyanines) generates metal NPs confined into carbon porous nanostructures.…”

“…[32][33][34] The material resulting from pyrolysis of FePc, which are iron NPs supported on nitrogen-doped carbon composites, exhibit catalytic activities for ammonia synthesis and compare favourably with benchmark industrial iron catalysts (iron doubly promoted catalyst, KM1 from Haldor Topsoe) when combined with alkali metals. [30,35] The important role of the alkali metal in these systems was illustrated by the fact that in the absence of the alkali metal, the reaction rate was dramatically decreased. [36,37] Thus, we found it exciting to elucidate the real effect of the alkali metal in the recently developed phthalocyanine-based catalysts for ammonia synthesis for Fe-based catalysts.…”

“…[36,37] Thus, we found it exciting to elucidate the real effect of the alkali metal in the recently developed phthalocyanine-based catalysts for ammonia synthesis for Fe-based catalysts. [30] , [38] Scheme 1. Schematic illustration for the preparation of promoted FePc catalysts towards ammonia synthesis.…”

Facilitating green ammonia manufacture under milder conditions: what do heterogeneous catalyst formulations have to offer?

“…17,49 However, the same does not hold for ammonia synthesis at lower temperatures and pressures, wherein a highly active catalyst is paramount to achieve satisfactory performance. At a pressure of 10 bar and a weight hourly space velocity (WHSV) of 12 000 mL g cat −1 h −1 (H 2 /N 2 = 3 : 1), an iron-based commercial HB catalyst yields an ammonia productivity of approximately 1900 μmol g −1 h −1 at 700 K, which falls to 600 μmol g −1 h −1 at 600 K. 50 However, the corresponding equilibrium ammonia composition increases from around 2 mol% at 700 K to 10 mol% at 600 K for an operating pressure of 10 bar. Therefore, the decreased productivity of the HB catalyst at lower temperatures, despite the increase in the thermodynamically permissible ammonia concentration, establishes the necessity to explore novel catalysts for use under milder reaction conditions.…”