Hydrodeoxygenation of bio-oil over mo based catalysts : assessment via model compounds and their mixtures

In recent decades, biomass attracted a great deal of attention as an alternative source for fuels and chemicals produced from fossil sources. When aiming for liquid bio-fuels, fast pyrolysis emerges as one of the prominent technologies. Major challenges in direct fast pyrolysis utilization are associated with high content of oxygenated organics in the produced bio-oil with high degree of functionalization. Present thesis applies catalytic hydrodeoxygenation as a promising route to reduce oxygen content in bio-oil by making use of model compounds. This thesis investigates alternative Mo based catalysts with varying catalyst properties to assess their performance during anisole hydrodeoxygenation through kinetic experimentation and material characterization. Through which, different factors affecting catalysts’ activity, stability and deoxygenation selectivity have been studied in detail and valuable insights are gathered. Subsequently, the potential to extrapolate the information obtained on bio-oil model compounds’ hydrodeoxygenation to more complex feedstock is explored using aromatics, aliphatic (C6, C7) carboxylic acids, aldehydes, alcohols and their mixtures. Present thesis lays a good foundation for the extension of knowledge on catalyst and operating conditions requirements for bio-oil catalytic upgrading

Effect of composition and preparation of supported MoO3 catalysts for anisole hydrodeoxygenation

A series of zirconia supported molybdenum oxide materials with Mo loadings of 7, 12, and 19 wt% were synthesized using incipient wetness impregnation. The as synthesized oxide materials were further modified under H-2/CH4 (80/20%, v/v) at 550 and 700 degrees C. The obtained catalysts were characterized by ICP-OES, XRD, Raman spectroscopy, H-2-TPR, NH3-TPD, XPS, (S) TEM-EDX, BET, CHNS and CO chemisorption. While the Mo species, i.e., MoO3 and Zr(MoO4)(2), in the 7 wt% Mo loaded material were found to be of rather amorphous nature, their crystallinity increased significantly with Mo loading. The anisole hydrodeoxygenation performance of the catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. A predominant selectivity towards hydrodeoxygenation and methyl transfer reactions rather than to hydrogenation was observed, irrespective of the Mo loading and further treatment, yet interesting differences in activity were observed. The highest anisole conversion was obtained on the catalyst(s) with 12% Mo loading, while the 7% Mo loaded one(s) exhibited the highest turnover frequency (TOFanisole) of 0.15 s(-1). CO chemisorption, XPS analysis and kinetic measurements indicate that treatment under H-2/CH4 slightly reduced the initial anisole conversion, yet enhanced catalyst stability as well as TOF, probably due to the increased amounts of Mo5+ species. The importance of appropriate tuning of the reduction and/or preparation procedures has been addressed to improve the catalysts' performance during anisole HDO

Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO

A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole <40%) at identical operating conditions. Titania supported catalysts exhibited rather higher stability compared to zirconia and alumina catalysts over 50 h time on stream (TOS), while zirconia catalysts displayed the highest HDO selectivity (up to 86%). Characterization studies of pre and post-reaction catalysts indicate Mo5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.publishedVersio

Oxygen functionality and chain length effects in HDO : impact of competitive adsorption on reactivity

The unavoidable and significant impact of compounds with different oxygen functionalities and carbon number on each other in hydrodeoxygenation (HDO) has been experimentally assessed over NiMo and CoMo catalysts in a wide temperature range from 100 degrees C to 350 degrees C, at a total pressure of 6 MPa, a feed to catalyst ratio of 1.22 g(oxygenate) g(cat)(-1)h(-1) and a concentration of 1.5 wt% of each oxygenated compound in n-decane. Overall, the model component conversion over the NiMo catalyst was higher than that over the CoMo catalyst. Compounds with an aldehyde functionality exhibited higher reactivity compared to compounds of the same chain length with a carboxylic acid or an alcohol functionality. The presence of carboxylic acids in feed mixtures along with aldehydes and aromatic oxygenates, shifted the conversion of the latter two to higher temperatures. This behavior could be attributed to competitive adsorption effects between the components with different functionalities and chain lengths