Operando study in temperature and pressure of the conversion of syngas loaded with typical impurities derived from biomass to methane and higher hydrocarbons. – BioSyngOp

All reference and operando tests were carried out under simulated reaction conditions of temperature and pressure up to 300 °C and from atmospheric pressure to 4 bars. The comparison of the reaction rate and product selectivity at the exit of the spectroscopic cells ensured that meaningful data were collected. This work resulted in a better understanding of the effect of the bio-poisons on typical syngas conversion catalysts, which helped rationalising future catalyst and process designs (which was not done here).
Several operando spectroscopic cells (i.e. FTIR cells and a novel cell enabling magnetic measurements) were used to monitor the changes happening to the catalysts and draw structure-activity relationships. The combination of these complementary spectroscopic techniques allowed probing the surface and bulk of the catalysts. The FTIR analysis focussed on the detection of i) carbonyl species, main surface intermediates, which also characterise the nature and quantity of metal surface sites and ii) spectators adspecies, mostly related to the supports. The coupling of SSITKA and FTIR techniques allowed discriminating spectator species from potential surface intermediates.

A direct relationship between the rate of formation of methane and entre the surface concentration of adsorbed CO was observed. This observation demonstrate the relevance of the operando techniques consisting in the monitoring of catalytic surface at work. The effects of the two most potent poisons, sulfur and chlorine, were evidenced and structure-activity relationships were proposed. The project partners will suggest more resistant formulations based on these results.

On the range of pollutants investigated, only a handful were deleterious to the catalytic activity of methanation and Fischer-Tropsch catalysts. The coupling of kinetic and spectroscopic techniques has enabled determining the nature of the most active sites, thereby suggesting improved formulations. Catalysts that are resistant to sulfur and chlorine have yet to be found and therefore more work is needed to identify S and Cl-resistant materials if a process free of purification steps is to be used.

Four publications are already published in international journals and several others are submitted. Two invited keynote lectures were given, two oral presentations and four posters were reported at international conferences. Several others communications are planned.

This project addresses crucial technological problems related to the utilisation of synthesis gas derived from biomass gasification (biosyngas: mixture of CO, CO2, H2 and impurities), thus pertaining to the wider societal agendas dealing with global warming and local production of cheap and sustainable fuels and chemicals. A major barrier in the commercialisation of biomass gasification is the presence of bio-impurities such as NH3, HCl, H2S and tars in the gas products that are detrimental to downstream processes.

Two important downstream processes are the conversion of syngas to (i) methane and light hydrocarbons (Substitute Natural Gas, SNG) and (ii) higher hydrocarbons (Fischer-Tropsch synthesis, FT). The exact role and effects of biomass-derived impurities on the catalysts used for these reactions are poorly known and this project will investigate these fundamental aspects using a set of model poisons: NH3, HCl, H2S, heptane and toluene. The operating conditions will be adapted to the possibilities of the operando techniques used for investigating ageing mechanisms.

Activity data measured using a pure CO/H2 feed over a set of reference catalysts (e.g., Ni and Co-based materials for the production of SNG and higher hydrocarbons, respectively) are already available to the partners. These data will be compared to those measured in the same feed to which the bio-poisons will be added individually or concomitantly. These catalytic tests will be carried out initially in traditional fixed bed reactors to assess the effect of poisons. These data will be complemented by steady-state isotopic transient kinetic analysis (SSITKA) to determine the number of reactant adsorption sites and residence time distribution of intermediates before, during and after contacting the catalysts with the poisons.

Several operando spectroscopic cells (i.e. FTIR and X-ray absorption spectroscopy (XAS) cells and a novel cell enabling magnetic measurements) will be used to monitor the changes happening to the catalysts and draw structure-activity relationships. The combination of these complementary spectroscopic techniques allows probing the surface and bulk of the catalysts. The magnetic and XAS techniques probe the oxidation state and dispersion of the metal used. The FTIR analysis will focus on the detection of i) carbonyl species, main surface intermediates, which also characterise the nature and quantity of metal surface sites and ii) spectators adspecies, mostly related to the supports. The coupling of SSITKA and FTIR techniques will allow discriminating spectator species from potential surface intermediates.

All reference and operando tests will be carried out under realistic reaction conditions of temperature and pressure similar to those used in real processes, up to 300 °C and from atmospheric pressure to 30 bars. The comparison of the reaction rate and product selectivity at the exit of the spectroscopic cells will ensure that meaningful data are being collected. This work should result in a detailed understanding of the effect of the bio-poisons on typical syngas conversion catalysts, which will help rationalising future catalyst and process designs (not to be done here).

The expertise of the partners is complementary. UCCS is expert in the area of syngas conversion, catalyst characterization by synchrotron techniques, kinetics and catalyst testing in fixed bed, slurry and milli-reactors. Ircelyon expertise includes fossil- and bio-fuel processing, on-line analysis of petrochemical fractions, mechanistic and modelling studies using transient techniques and magnetic measurements. LCS is expert in the design and operation of operando FTIR cells. Three post-doctoral assistant researchers will be hired and participate in most of the tasks, also spending time at each laboratory. The results will be disseminated through traditional means and a session dedicated to syngas conversion during a Spectroscopy School organised by the LCS every 3 years.