Controlled ensemble size and elucidation of structure-sensitivity: a new approach in nitride catalysis

Lead Research Organisation: University of Glasgow
Department Name: School of Chemistry

Abstract

Most industrial chemical processes use catalysts to enhance the rate at which a reaction proceeds or to favour a specific product. Catalysts thus lead to significant savings in the energy used for large scale processes and a reduction in the amount of waste generated. Amongst the catalysts applied, heterogeneous catalysts are the most practical due to the ease of their separation from product streams.
This project will combine synthetic and application based advances to metal nitrides which are an emerging class of heterogeneous catalyst with interesting and distinctive properties. The approach taken is to exert control over both the size and composition of active centres dispersed within a host matrix. Controlled ensemble size has proven to be a powerful approach with other categories of catalysts. We propose to develop novel materials with enhanced activity for ammonia synthesis, a vitally important reaction on a global scale for which some metal nitrides have already shown activity of potential interest for industrial application. We also plan to target high activities in two other important processes - ammonia decomposition, which is a potential clean hydrogen source for renewable energy applications, and ammoxidation, important in chemicals synthesis. The latter is a particularly challenging target which requires catalyst design that combines different functionalities within active centres.
Our programme combines the development of catalyst synthesis routes, which will be used to control the size and elemental composition of the catalytic sites with extensive catalyst testing, involving reactions performed under industrially relevant conditions.

Planned Impact

The work will design new catalysts and develop new catalytic processes. Heterogeneous catalysis is of key economic importance for the chemicals industry, which contributes £50 billion per annum to the UK economy. Furthermore, the identification of more active and/or more selective catalysts leads to significant environmental benefits by reducing energy requirements of processes, utilising starting materials more efficiently and reducing the amount of waste generated. We will concentrate on three reactions of significant economic and environmental impact:
(i) Ammonia synthesis uses the Haber-Bosch Process, directly combining N2 and H2 with iron-based catalysts. This 90 year-old high pressure, high temperature process accounts for 1% of global energy demand including purification of N2 and H2. However, it can be directly credited with sustaining the world's population through access to synthetic fertilisers and provides an important chemical reagent. Liquid ammonia is also a high energy density fuel that can readily be transported at moderate pressure, and hence ammonia synthesis is a potential means to store renewable energy in a versatile form. It is readily apparent that any improvement in the ammonia synthesis process could yield massive returns. Testing will be carried out in conjunction with Johnson Matthey Catalysts, an internationally-leading leading British-based manufacturer of industrial ammonia synthesis catalysts.
(ii) Ammonia decomposition is of current interest in relation to the development of the hydrogen economy. The liberated H2 is free from the presence of COx and can therefore be applied directly in PEM fuel cells, which are susceptible to poisoning by trace CO present in hydrogen generated by reforming. Some power stations employ selective catalytic reduction using NH3 to remove NOx from waste gas generated in fossil fuel combustion - NH3 decomposition catalysts could also be used to guard against NH3 slippage to the atmosphere.
(iii) thane ammoxidation yields acetonitrile, which is a solvent for many large-scale applications. Using an alkane as the hydrocarbon reactant is economically and environmentally desirable as the commoner alkene reactants are produced by an energy-intensive high temperature steam cracking route. In 2008/9, a worldwide shortage of acetonitrile resulted from the global reduction in capacity for acrylonitrile from which it is a by-product. Alternative production routes are needed to maintain stability of supply.
The project will develop generic methodology which will extend beyond the three targets outlined above to further catalytic processes and other applications. The postdoctoral researchers will need to develop new skills in their own fields (materials and catalysis) but will also benefit strongly from the broad combination of expertise required in this interdisciplinary project. The interactions with Johnson-Matthey will provide a strong industrial perspective to all those involved in the project, and will provide an opportunity to gain a high level of familiarity with industrial catalysis through direct involvement in their testing programmes.

Publications

10 25 50
 
Description The role of structure and composition for catalysts applied to the synthesis of ammonia, a product which sustains 40% of the world's population through access to synthetic fertiliser, has been probed. The particular focus of interest has been in the use of metal nitride catalysts and we have investigated the effect of preparation conditions and the inclusion of additional elements on their performance. For nickel molybdenum nitride catalysts it has been found that materials which are very effective can be prepared using a sol-gel based method to generate the oxide precursor which can then be easily transformed to the active catalytic phase under the reactant gas mixture at elevated temperature. This preparation method allows the controlled introduction of additional components and in doing so it has been found that cobalt containing nickel molybdenum phases can be prepared, although they have lower activity. A preparation route to high quality silicon nitride supports was developed and the incorporation of transition metals within this support has been accomplished for which it has been shown that vanadium - silicon nitride is a poor catalyst for making ammonia although it is very effective for making hydrogen and carbon by cracking methane which is of interest for the generation of carbon oxide-free feedstreams for low temperature fuel cell applications.
Exploitation Route The establishment of the sol-gel route for the preparation of ternary and quaternary nitrides is of interest in their application as catalysts and materials for other applications. Investigation of the catalytic performance of the Ni2Mo3N and CoNiMo3N systems for ammonia synthesis is useful in the development of enhanced understanding of such systems for the development of catalysts of improved activity. Silicon nitride has been demonstrated to be a suitable and effective support for the dispersion of transition metal species which is of interest for the development of methane cracking catalysts for the production of COx-free hydrogen.
Sectors Chemicals,Energy

 
Description Andrew Hector 
Organisation University of Southampton
Country United Kingdom 
Sector Academic/University 
PI Contribution The research team at Glasgow provide catalytic testing expertise on samples prepared by Southampton. Glasgow also performs detailed materials characterisation both pre- and post- catalytic testing.
Collaborator Contribution Southampton prepare a large number of candidate inorganic materials that are then tested for their ammonia synthesis ability at Glasgow.
Impact A number of academic publications have arisen from this collaboration in both catalytic and inorganic synthesis fields.
Start Year 2013
 
Description Dr. Nicolas Bion, University of Poitiers 
Organisation University of Poitiers
Country France 
Sector Academic/University 
PI Contribution This collaboration between Poitiers and Glasgow focusses on carrying out nitrogen isotopic exchange experiments in order to probe the mobility of lattice nitrogen within a range of catalytically relevant materials. The team at Glasgow were responsible for material preparation and sending personnel to the University of Poitiers to conduct the relevant experiments.
Collaborator Contribution The University of Poitiers provided experimental personnel and the experimental apparatus for the study.
Impact This collaboration has resulted in one publication and should result in at least one more peer-reviewed paper.
Start Year 2014
 
Description Prof. Wendy Flavell, University of Manchester 
Organisation University of Manchester
Country United Kingdom 
Sector Academic/University 
PI Contribution This collaboration focussed on carrying out depth-sensitive x-ray photoelectron experiments at the Elettra Synchrotron Trieste (Italy) in order to probe the relative quantities and oxidation states of the elements present in Co3Mo3N. The role of Glasgow in the collaboration was materials preparation, providing personnel for the experiment itself and in data analysis.
Collaborator Contribution The team at Manchester were responsible for securing beamtime for the experiment and for providing specialist knowledge on the technique -both from a theoretical and a practical point of view.
Impact This collaboration should result in a peer-reviewed publication (in preparation). It also led to additional experiments being performed on related systems.
Start Year 2014