Towards a molecular understanding of deactivation issues in methane reforming catalysts
Lead Research Organisation:
University of Glasgow
Department Name: School of Chemistry
Abstract
This research proposal brings together a grouping of specialists in surface chemistry, heterogeneous catalysis, solid state chemistry, infrared spectroscopy, Raman spectroscopy and inelastic neutron scattering spectroscopy to identify the critical factors responsible for maintaining hydrogen yields in methane reforming catalysts. Ormerod has already prepared, and partially characterised, a number of methane reforming catalysts that display a wide range of performance, in terms of hydrogen selectivity and operational lifetime. Whereas the standard formulations display the expected catalyst deactivation characteristics, some of the modified catalysts exhibit excellent hydrogen selectivity that can be maintained over extended periods of time, i.e. minimal deactivation is observed. A workplan is presented whereby the research team will develop a mechanistic understanding of why the 'good' catalysts favour high hydrogen selectivity and avoid the carbon laydown processes, that lead to the formation of surface oligermic species and, ultimately, catalyst deactivation. This multi-disciplinary and multi-institutional research proposal has direct connections to energy requirements of the UK chemical industry and, moreover, targets key areas of the science base as highlighted in the recent Whiteside's report and the EPSRC's Research Priorities and Opportunities document.
Publications
Hamilton N
(2014)
The application of inelastic neutron scattering to investigate CO hydrogenation over an iron Fischer-Tropsch synthesis catalyst
in Journal of Catalysis
Hamilton NG
(2013)
Vibrational analysis of an industrial Fe-based Fischer-Tropsch catalyst employing inelastic neutron scattering.
in Angewandte Chemie (International ed. in English)
Lennon D
(2014)
Inelastic neutron scattering studies of methyl chloride synthesis over alumina.
in Accounts of chemical research
Lennon D
(2013)
Characterisation of hydrocarbonaceous overlayers important in metal-catalysed selective hydrogenation reactions
in Chemical Physics
Lopez-Sanchez J
(2015)
The Preparation of a Residue-free, Alumina-supported Gold Catalyst by Decomposition of an Azido-Gold(III) Complex and an Evaluation of the Effectiveness of the Catalyst for the Hydrogenation of Propyne
in Zeitschrift für anorganische und allgemeine Chemie
Mark Ormerod (Author)
(2010)
Carbon deposition, sulphur poisoning and characterisation of hydrocarbonaceous overlayers formed during reforming
McFarlane A
(2013)
The application of inelastic neutron scattering to investigate the steam reforming of methane over an alumina-supported nickel catalyst
in Chemical Physics
McFarlane A
(2010)
The observation of equilibria present in stepwise gas phase hydrogenation reactions
in Catalysis Today
| Description | An important primary process for the chemical manufacturing industry involves the reforming of methane to produce 'synthesis gas' (carbon monoxide and hydrogen). This is normally achieved using alumina-supported nickel catalysts, however these catalysts are prone to deactivation over time, typically as a consequence of carbon laydown. Previously, physical analysis of these materials has tended to concentrate on measurements that focus on the carbon, not least because the presence of water in the reaction system complicates hydrogen quantification. This work is novel in that it has used the technique of inelastic neutron scattering (INS) to determine how hydrogen is being partitioned within the reaction system. The two principle variants of methane reforming have been analysed. The majority of our effort has concentrated on using CO2 as an oxidant, the so-called 'dry' reforming process. Once the techniques and methodologies had been developed to investigate that reaction, we then moved on to study the industrially favoured methane steam reforming reaction. In order to make optimum use of the new INS data, it was essential for us to characterise the reaction systems using the more conventional tools of heterogeneous catalysis. Consequently, the INS studies were backed up by the following arsenal of experimental techniques: micro-reactor testing, temperature-programmed oxidation, temperature-programmed hydrogenation, infrared spectroscopy, X-ray diffraction, transmission electron microscopy, UV-visible absorption spectrophotometry and Raman scattering. Isotopic substitution experiments provided additional insight in to the surface processes active within this intricate reaction system. For the 'dry' reforming reaction, two experimental regimes were investigated: (i) where amorphous carbon is formed as a by-product and (ii) where filamentous carbon is formed as a by-product. In both cases the nickel catalysts were seen to be very efficient at cycling hydrogen but less so at forming carbon monoxide. The quantity and form of the hydrogen retained at the catalyst was determined in both cases and when combined with the conventional analysis, primarily addressing carbon-related matters (for example temperature-programmed oxidation measurements), surface C:H ratios were determined. This heightened awareness of how hydrogen was being partitioned within the reaction system then enabled refinements of existing reaction schemes to be proposed. Further, the isotopic substitution measurements highlighted the interconnectivity extant in this reaction system, where the oxidant contributes to carbon laydown, with carbon being cycled via (i) the reverse water gas shift reaction and (ii) the Boudouard reaction. The steam-reforming reactions were operated at industrially relevant conditions (steam lean and high temperature) where carbon retention manifested itself in the well-established formation of 'whiskers'. Hydrogen retention within the catalyst matrix was considerably lower than that observed in the 'dry' reforming studies, despite hydrogen being associated with the oxidant. The reaction scheme proposed for the 'dry' reforming reactions was readily adapted to the steam reforming variant. In neither case was it necessary to invoke a role for surface hydroxyl groups. Seven papers have resulted from these studies. Four are already published. One paper is currently under review and drafts have been prepared for a further two papers, one of the latter being an invited submission connected with an invited presentation at the 2012 American Chemical Society Spring meeting. Finally, two additional outcomes connected in part with this project: (i) it has spurned a new project with a major chemical manufacturing company and (ii) the ISIS Facility has up-graded its laboratory facilities to better accommodate catalyst based INS experiments. |
| Exploitation Route | The work was generic in nature and can be applied to a wide range of heterogeneously catalysed reaction systems. Details of the methodology employed for the inelastic neutron scattering measurements were published in a separate paper. We are now working with a UK based chemical technology company to use the techniques developed from this study to apply then to some of their catalytic systems. |
| Sectors | Chemicals |
| Description | An important primary process for the chemical manufacturing industry involves the reforming of methane to produce 'synthesis gas' (carbon monoxide and hydrogen). This is normally achieved using alumina-supported nickel catalysts, however these catalysts are prone to deactivation over time, typically as a consequence of carbon laydown. Previously, physical analysis of these materials has tended to concentrate on measurements that focus on the carbon, not least because the presence of water in the reaction system complicates hydrogen quantification. This work is novel in that it has used the technique of inelastic neutron scattering (INS) to determine how hydrogen is being partitioned within the reaction system. The two principle variants of methane reforming have been analysed. The majority of our effort has concentrated on using CO2 as an oxidant, the so-called 'dry' reforming process. Once the techniques and methodologies had been developed to investigate that reaction, we then moved on to study the industrially favoured methane steam reforming reaction. Seven papers have resulted from these studies. Four are already published. One paper is currently under review and drafts have been prepared for a further two papers, one of the latter being an invited submission connected with an invited presentation at the 2012 American Chemical Society Spring meeting. Finally, two additional outcomes connected in part with this project: (i) it has spurned a new project with a major chemical manufacturing company and (ii) the ISIS Facility has up-graded its laboratory facilities to better accommodate catalyst based INS experiments. . The project met all of its original objectives withthe EXAFS measurements which could not be performed due to the demise of the Daresbury synchrotron. Analysis of catalysts active for reforming of methane with steam and carbon dioxide were studied. The partitioning of hydrogen throughout both reactions systems was dertermined. The work has spurned two new projects sponsored by a major chemical manufactoring organisation. Beneficiaries: Wide dessemination of scientific outcomes to academic and industrial communities. Contribution Method: Approach from major chemical manufacter to initiate follow-on project to use generic techniques applied in this project to investigate aspects of some of their catalytic systems. |
| Sector | Chemicals |
| Impact Types | Cultural |
| Description | ISIS |
| Amount | £50,000 (GBP) |
| Funding ID | Molecular Spectroscopy - Catalysis |
| Organisation | University of Oxford |
| Department | Oxford University Innovation |
| Sector | Private |
| Country | United Kingdom |
| Start | 10/2011 |
| End | 06/2012 |
| Description | ISIS |
| Amount | £50,000 (GBP) |
| Funding ID | Molecular Spectroscopy - Catalysis |
| Organisation | University of Oxford |
| Department | Oxford University Innovation |
| Sector | Private |
| Country | United Kingdom |
| Start | 10/2011 |
| End | 06/2012 |