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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NewCat4Bio (Innovative sol-gel strategies for the production of homogeneous, hydrothermally stable, andporous mixed metal oxide catalysts for biomass conversion applications)

Teaser

Summary

Mixed metal oxides play an important role in many industrial applications, as adsorbents, sensors, electrolytes in batteries, heterogeneous catalysts, etc. Among them, metallosilicates are particularly useful in heterogeneous catalysis, since their acido-basic properties can be tuned by the amount, nature and dispersion of the metals incorporated in the silica matrix, by synthesis conditions, by post-treatments, etc. Metallosilicates are used as catalysts in epoxidation of alkenes, cracking, isomerization reactions, etc. Nowadays they are applied in the biomass and biofuel sector, where they catalyze the dehydration of bioalcohols, (trans)esterification and hydrolysis in oleochemistry, biopolymer hydrolysis, condensation reactions, etc. However for this modern purpose the performance of metallosilicates is not fully satisfactory, mainly due to their low stability in the presence of water. In this project, we proposed to explore and evaluate non-hydrolytic sol-gel processing of novel metallosilicate catalysts to tackle these challenges, thereby supporting the efficiency and competitiveness of biomass valorization. The main objective of our research project was to take advantage of the non-hydrolytic sol-gel chemistry to prepare, characterize and apply new homogeneous, hydrothermally stable, and porous mixed metal oxide catalysts with high performance in biomass conversion applications. In terms of catalyst synthesis, we (i) studied the dispersion of the metal in silica matrices, (ii) tried to improve the hydrothermal stability by using appropriate hybrid precursors and surface modifiers with hydrophobic moieties and (iii) controlled porosity by the use of various solvents, templates, and precursors. These catalysts were characterized by an array of advanced physico-chemical tools to evaluate the effects of preparation parameters on the desired properties â€“ homogeneity, hydrothermal stability and texture. The materials were evaluated as heterogeneous catalysts in a topical reaction of biomass valorization: ethanol dehydration to ethylene. We followed the influence of the materials properties on catalyst activity, selectivity and lifetime. The main conclusions are as follows: (i) non-hydrolytic sol-gel chemistry allows to prepare metallosilicates with a high homogeneity of metal dispersion within silica matrices, this in turn leads to improved acido-basic properties and markedly better catalytic activity and selectivity to ethylene in comparison to commercial benchmarking catalysts, (ii) a broad variety of organic groups were introduced into the metallosilicate materials, direct bond between Si and aromatic groups is not stable under the reaction conditions, alkyl groups are stable and lead in some cases to an improvement of catalytic activity, and (iii) catalyst lifetime depends on the textural properties and strength of acid sites, some samples proved to be highly stable during our stability tests.

Work performed

This research project consisted of 4 Work Packages (WP): Synthesis, Characterization, Catalytic testing, and Management & Dissemination. Work Package 1: Synthesis aimed at the preparation of homogeneous, (hydro)thermally stable and porous mixed metal oxides. The research work, which fulfiled the WP1, relied on the NHSG chemistry enriched with precursors with hydrophobic organic groups and texture control (mainly by templating strategies).
Work Package 2: Characterization included some routine analysis of mixed metal oxides as well as advanced and original characterization experiments (especially surface characterization). It also encompassed the training on analytical techniques, which were new for the Researcher: XPS, ToF-SIMS and TPD of ammonia. A manuscript comparing various NHSG synthetic routes in terms of their impact onto the material\'s properties â€“ homogeneity, (hydro)thermal stability and texture - was prepared on the basis of results obtained mainly in these two work packages (submitted). These results were also communicated at an international conference (6th International Conference on Multifunctional, Hybrid, and Nanomaterials).
The Work Package 3: Catalytic testing was completed first by mounting (revamping) of the catalytic reactor and learning how to set the correct parameters for catalytic reactions. Then we performed some preliminary catalytic tests on our materials. Since our materials exhibited markedly improved activity and selectivity to ethylene in comparison to commercial silica-alumina, we continued with catalytic testing on our samples in ethanol dehydration, ran the analytical tools, analysed the data and defined, which characteristics were crucial for obtaining of active catalysts. Based on these data two manuscripts are in preparation summarizing the results of the research project with the focus on the catalytic part of research. These data were also presented at an international conference (Europacat 2019).
Finally the Work Package 4: Management & Dissemination took place during the whole project duration. The researcher and the supervisor worked hand in hand at the dissemination tasks. In addition to already described preparation of manuscripts and conference presentations, we engaged in public dissemination (blog and Twitter, Printemps des Sciences).

Final results

1/ Novel metallosilicate catalysts for ethanol dehydration were synthesized and fully characterized.
2/ Hydrothermal stability of hybrid metallosilicate catalysts under the conditions relevant for ethanol dehydration was described for the first time. Striking difference in stability was observed between the samples containing Si-C(sp2) and Si-C(sp3) bond.
3/ Catalytic activity, selectivity, and stability was studied. NHSG catalysts displayed activity and selectivity to ethylene better than commercial benchmark. Stability was improved by proper tuning of acid site strength, but a robust porous network was needed as well.
4/ The hydrophobicity/hydrophilicity and the impact of organic groups incorporation was studied as well. Interestingly, the presence of hydrophobic organic groups played only a minor role in comparison to the number of highly hydrophilic acid sites. Consequently, the activity in ethanol dehydration was fully governed by the number of acid sites.
All these results are very important for the emerging bio-based industry, since ethanol used for dehydration and ethylene production may come from bio-sources (sugar based and transformed by fermentation).