Lignin-derived Model Compound Research Articles

Improved nickel nanocatalysts for selective cleavage of lignin model compounds and lignin

The selective hydrogenolysis of lignin offers a promising avenue for converting lignin into valuable chemicals and fuels. However, the development of highly active catalysts for this process remains challenging. In this study, a series of Nix/Al2O3 catalysts were synthesized by calcining and reducing layered double hydroxides (LDHs) precursors. These catalysts were evaluated for their effectiveness in catalyzing the conversion of lignin-derived model compounds (2-phenoxy-1-phenylethanol and diphenyl ether). Remarkably, the optimized Ni3/Al2O3 catalyst demonstrated exceptional performance in cleaving C–O bonds, achieving complete conversion with high selectivity for monomers product under reaction conditions of 200 °C, 1 MPa H2, and 1 h. The catalyst's outstanding performance can be attributed to its relatively large specific surface area, Ni loading exceeding 50 wt%, well-dispersed Ni metal particles, abundant surface oxygen vacancies, and a significant number of acid sites. Additionally, the hydrogenolysis of lignin using the Ni3/Al2O3 catalyst resulted in a substantial production of monophenols (15.0 wt%). This study introduces a novel approach for tailoring highly active Ni nanocatalysts and highlights the capability of Nix/Al2O3 catalysts to efficiently cleave C–O bonds in lignin under mild reaction conditions.

Hydrodeoxygenation of lignin bio-oil model compounds and surrogate mixtures over zeolite supported nickel catalysts

Bifunctional catalysts based on nickel supported on ZSM-5 and BETA zeolites were studied in the hydrodeoxygenation of lignin derived model compounds as well as in surrogate mixtures simulating the light fraction of lignin fast pyrolysis bio-oil. A screening of the hydrodeoxygenation reaction conditions (temperature, time, H2 pressure, catalyst amount) was carried out using the simplest phenolic compound, phenol. As in real lignin bio-oils more complex phenolic compounds are present, a series of relevant alkyl- and methoxy-substituted phenol and benzene (o- and m-cresol, catechol, anisole, guaiacol, syringol, creosol and 1,2,3-trimethoxybenzene) were also investigated as feedstocks. Furthermore, the effect of the different porous and acidic properties of the zeolitic supports was investigated in the hydrodeoxygenation of guaiacol. The conversion of the model phenolics and the yield of the respective (alkyl)cyclohexanes at relatively mild conditions (220 °C, 50 bar H2, 1 h) were in the range of 80–100% and 47–83%, respectively, being dependent mainly on the complexity/side-chain group of the phenolic/benzylic ring and on the balanced content of Brønsted acid sites of increased strength. Regarding the hydrodeoxygenation of the surrogate mixture (C7-C10 phenolics), 100% hydrodeoxygenation efficiency was achieved towards >60% yield of (alkyl)cyclohexanes (C6-C9 hydrocarbons). All hydrodeoxygenation tests were conducted in hexadecane as solvent/substrate in order to simulate model co-processing (i.e. bio-based phenolics with petroleum derived feedstocks) conditions. Reusability tests revealed the stability of the catalysts which showed partial (30%) deactivation after the third catalytic cycle.

Hydrodeoxygenation of Oxygenates Derived from Biomass Pyrolysis Using Titanium Dioxide-Supported Cobalt Catalysts.

Bio-oil upgrading to produce biofuels and chemicals has become an attractive topic over the past decade. However, the design of cost- and performance-effective catalysts for commercial-scale production remains a challenge. Herein, commercial titania (TiO2) was used as the support of cobalt (Co)-based catalysts (Co/TiO2) due to its low cost, high availability, and practicability for commercialization in the future. The Co/TiO2 catalysts were made with two different forms of TiO2 (anatase [TiO2-A] and rutile [TiO2-R]) and comparatively evaluated in the hydrodeoxygenation (HDO) of 4-propylguaicol (4PG), a lignin-derived model compound. Both Co/TiO2 catalysts promoted the HDO of 4PG following a similar pathway, but the Co/TiO2-R catalyst exhibited a higher activity in the early stages of the reaction due to the formation of abundant Ti3+ species, as detected by X-ray photoelectron spectroscopy (XPS) and hydrogen-temperature programed reduction (H2-TPR) analyses. On the other hand, the Co/TiO2-A catalyst possessed a higher acidity that enhanced propylcyclohexane production at prolonged reaction times. In terms of reusability, the Co/TiO2-A catalyst showed a higher stability (less Co leaching) and reusability compared to Co/TiO2-R, as confirmed by transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses. The HDO of the real bio-oil derived from pyrolysis of Leucaena leucocephala revealed that the Co/TiO2-A catalyst could convert high oxygenated aromatics (methoxyphenols, dimethoxyphenols, and benzenediols) to phenols and enhanced the phenols content, hinting at its potential to produce green chemicals from bio-feedstock.

Co-processing of fossil feedstock with lignin-derived model compound isoeugenol over Fe-Ni/H-Y-5.1 catalysts

Co-processing of n-hexadecane with lignin derived isoeugenol as a model compound was investigated in this work using low-cost mono- and bimetallic iron and nickel supported on H-Y-5.1 zeolite. Different Fe-Ni metal ratios in the catalyst led to different reaction rates of processes and product distribution. The presence of just 0.26 wt% isoeugenol in the mixture with n-hexadecane made hydroisomerization-hydrocracking of the latter two-fold less active. Catalysts with smaller metal particle sizes, lower than 6 nm were more efficient pointing out on structure sensitivity. Extremely high activity in co-processing was obtained over 2 wt% Fe – 8 wt% Ni/H-Y-5.1 catalysts with the median metal particle size of 4.6 nm and metals-to-acid site ratio of 8.6. Fe catalyst were much less active in isoeugenol hydrodeoxygenation, while high cracking activity of hexadecane was observed in the presence of Ni. Alkylation of n-hexadecane was a feature of 8 wt% Fe – 2 wt% Ni/H-Y-5.1, whereas, over the 5 wt% Fe – 5 wt% Ni/H-Y-5.1 bifunctional catalyst no undesired oxygen-containing cyclic products were detected. This catalyst exhibited the highest hydrogen consumption according to temperature programmed desorption, which can serve as a marker for efficient hydrodeoxygenation. The spent catalysts contained ca 40 wt% of coke with predominantly aliphatic species.

Non-precious metal catalysts supported by activated carbon and TiO2–SiO2: Facile preparation and application for highly effective hydrodeoxygenation of syringol–a lignin-derived model compound

Non-precious metal catalysts (10 wt% loading) over activated carbon (AC) and TiO2–SiO2 supports prepared via incipient wetness impregnation and spray pyrolysis were characterized using various analytical techniques. AC with a higher surface area displayed a better ability than TiO2–SiO2 in syringol conversion and hydrocarbon product selectivity. Compared to Fe and NiFe catalysts, the Ni catalyst showed more effective hydrodeoxygenation performance in terms of syringol conversion, selectivity, and the yield of oxygen-free products (mainly alkylbenzenes via transalkylation reactions). The deoxygenation ability was confirmed via the moisture and COx release. The highest syringol conversion (99.91%) could be obtained using 10 wt% Ni/AC. Generally, syringol hydrodeoxygenation in a fixed-bed reactor followed the main reaction pathway of the hydrogenolysis of CAr–OC(sp3) and CAr–OH rather than the hydrogenation of the benzene ring, producing p-xylene, phenol, and cresols as the major products. Besides metallic catalysts and supports, the reaction temperature and the total flow rate of the H2/Ar mixture on hydrodeoxygenation performance were also investigated. Our study provides a promising potential in the utilization of non-precious metals and biomass-derived AC to remove oxygen from bio-oil model compounds, contributing to the development of sustainable renewable energy.

Solventless hydrodeoxygenation of isoeugenol and dihydroeugenol in batch and continuous modes over a zeolite-supported FeNi catalyst

A low-cost bimetallic bifunctional 5–5 wt% FeNi/H-Beta-300 catalyst was investigated in solventless hydrodeoxygenation of lignin-derived model compounds isoeugenol or dihydroeugenol in batch and continuous modes.

The selective hydrodeoxygenation of guaiacol to cyclohexanol over cobalt-modified TS-1 catalysts

A Co-modified zeolite (Co/TS-1) catalyst is prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of the lignin-derived model compound guaiacol under mild conditions at 1 MPa H2 and 200 °C. According to the systemic experimental investigations including reduction temperatures, metal loading and reaction time, it is found that the guaiacol conversion and cyclohexanol selectivity over guaiacol HDO are significantly improved by regulating the Ti content, Co content and reduction temperature, in which 5.0%Co/TS-1 (Si/Ti = 110) reduced in 600 °C shows the superior HDO performance with 94.3% guaiacol conversion and 88.7% cyclohexanol selectivity. Combined with XRD, TEM, BET, NH3-TPD, Py-IR, H2-TPR, UV–Vis and XPS characterizations, it is confirmed that the introduction of appropriate Ti could modulate the catalyst Lewis acid sites and the interaction between Co and support to affect the metal reduction degree, to realize the improvement of the substrate adsorption and exposing more metallic Co0 active sites, resulting in higher HDO performance. In addition, the reaction pathway of guaiacol HDO to cyclohexanol over Co/TS-1 is proposed via demethoxylation of guaiacol to generate reaction intermediate phenol.

Effect of the Support on Rhenium Carbide in the Hydrodeoxygenation of Guaiacol as Lignin-Derived Model Compound

The effect of support on the formation of rhenium carbide in the hydrodeoxygenation (HDO) of guaiacol as a lignin-derived compound was evaluated. Catalysts were prepared by incipient wetness impregnation, carburized at 650 °C under a mixture 25/75 of ethylene/hydrogen, and characterized by XRD, N2-physisorption, TPR, TPD of NH3 or isopropylamine (IPA), and XPS. The results have demonstrated that the support choice affects the carburization of rhenium. Indeed, over non-acidic support (e.g., SiO2), limited carburization of the metal was observed, while over ZrO2 and Al2O3, carburization of rhenium occurred, and different carbidic species were obtained depending on the surface and chemical identity of the support. The rhenium carbide species obtained over ZrO2 was the most active and selective toward benzene (22% at 98% of conversion).

Facile water-free synthesis of noble metal-containing hydrotalcites-derived materials and their application for hydrotreatment of anisole

A novel, solvent-free, atom-efficient, and environmentally friendly method for preparing nickel-based hydrotalcite (HT) materials containing group VIII metals was established. A series of nickel-based (NiRu, NiRh, NiIr, NiSn, NiFe, NiCo, NiIn, and NiAl) HT-type materials were successfully synthesized using a facile water-free solid-state grinding method. The precursor-gel obtained by solid-state grinding facilitates efficient hydrolysis of metal salts by the use of ammonium hydroxide and results in the formation of layered HT materials. The presence of layered HT structure was evident from the powder X-ray diffraction (XRD) analysis. The method provides the complete conversion of metal precursors into the corresponding HT materials in an atom-efficient manner. The developed nickel-based HT materials were highly efficient and reusable catalysts for the hydrotreatment of the lignin-derived model compound, anisole. Among the several catalysts prepared, the one based on nickel-ruthenium catalysts showed complete conversion of anisole with 86% selectivity toward cyclohexane under optimum reaction conditions. The presence of in-situ generated metallic nickel‒ruthenium species on the surface of the catalyst, as evident from XPS, TEM, and XRD analysis of the spent catalyst, was responsible for the observed superior catalytic activity.

Catalytic Hydrodeoxygenation of Guaiacol to Cyclohexanol over Bimetallic NiMo-MOF-Derived Catalysts

Lignin is an attractive renewable source of aromatics with a low effective hydrogen to carbon ratio (H/Ceff). The catalytic hydrodeoxygenation (HDO) of lignin-derived model compounds is a key strategy for lignin upgrading. In this work, the HDO of guaiacol, a typical lignin-derived compound, was carried out over metal–organic framework (MOF)-derived Ni-based catalysts. A monometallic Ni-MOF catalyst and different ratios of bimetallic NiMo-MOF catalysts were synthesized by a hydrothermal process, followed by a carbonization process. Among these catalysts, Ni3Mo1@C exhibited an excellent catalytic performance, affording a guaiacol conversion of 98.8% and a cyclohexanol selectivity of 66.8% at 240 °C and 2 MPa H2 for 4 h. The addition of Mo decreased the particle size of the spherical structure and improved the dispersion of metal particles. The synergistic effect between Ni and Mo was confirmed by various means, including ICP, XRD, SEM, TEM, and NH3-TPD analyses. In addition, the effect of the reaction temperature, time, and H2 pressure during the HDO process is discussed in detail.

Exploring the reaction chemistry of biomass upgrading over HZSM-5 catalyst through model compounds

The catalytic fast pyrolysis of 17 biomass-derived model compounds over HZSM-5 was conducted in double microfixed-bed reactors (DFBRs) at 500 °C. Our single photoionization mass spectrometer (SPI-MS) allows the real-time monitoring the dynamics of volatiles formation as a function of catalyst deactivation, which provides interesting information on reaction chemistry of biomass catalytic upgrading. The roles of some important intermediates (e.g., benzofurans, benzaldehydes, benzenediols etc.) and their conversion in biomass upgrading are comprehensively discussed. The network of reaction pathways for the conversion of chosen model compounds is also proposed based on the release trend of different products. Strikingly, the favorite formation pathways of large aromatic hydrocarbons in catalytic upgrading are considered to be different between carbohydrate- and lignin-derived model compounds. The level of HZSM-5 deactivation is closely associated with their ability to remove the number of oxygen atoms in feeding model compounds. Besides, the impact fact on the catalyst deactivation in the upgrading of lignin model compounds is discussed. Overall, the performance of commercial HZSM-5 in biomass upgrading is unsatisfactory and has limited relevance to the type of model compounds except for oxygen-free intermediates.

Engineered Pseudomonas putida for biosynthesis of catechol from lignin-derived model compounds and biomass hydrolysate

Catechol is an industrially relevant chemical with myriad applications. Its production via chemical route suffers from several drawbacks the major being a non-green and nonselective route. Currently, bio-based products using biocatalyst are gaining attention due to the growing environmental and health hazards concerns over the use of petroleum-derived feedstock. Lignocellulosic biomass serves as a promising feedstock. Lignin valorization is the demand of the current scenario which is complicated task by its complexity, heterogeneity and diversity of lignin structures posing limitations toward lignin valorization via chemical routes. There are several microorganisms that possess the ability to metabolize lignin monomers via their central metabolic pathways and this paves the way to the synthesis of a number of products. Pseudomonas putida KT2440 is one such organism and was chosen for genetic manipulations for catechol biosynthesis using lignin-derived model compounds and biomass hydrolysate stream comprising of various lignin monomers. Catechol production was engineered by diverting various lignin monomers and addressing the identified metabolic bottlenecks particularly vanillic acid accumulation toward catechol biosynthesis. The engineered strain could convert the model lignin monomers as well as monomers in the biomass hydrolysates to catechol and vanillic acid in more than 60% and 90% molar yields, respectively.

Electrochemical upgrading of depolymerized lignin: a review of model compound studies

This review addresses advancements and challenges in the use of electrochemical methods as a means of upgrading lignin-derived model compounds to value-added products.

Hydrodeoxygenation of 2-methoxy phenol: Effects of catalysts and process parameters on conversion and products selectivity

The hydrodeoxygenation (HDO) of 2-methoxy phenol (MP), a lignin-derived compound, has massive prospective for valuable compounds production. The lignin derived model compounds can be used for production of green chemicals. The model compound MP conversion into cyclohexane was investigated over Ru metal loaded on various supports (ZSM-5, Y-zeolite, β-zeolite, COK-12, mordenite, ZrO2, and TiO2). The catalytic properties such as the acidic sites, pore size, and morphology influenced the HDO activity and selectivity of the cyclohexane. The yield of cyclohexane increases up to optimum acidity further increases the acidity of the catalyst, the product yield decreased. The experiments carried out at temperature range of 200–300 °C, and 1–25 bar hydrogen pressure in a fixed bed reactor. The parameters greatly influenced the HDO as well as the cyclohexane yield, selectivity, and MP conversion. The highest conversion (100%) and yield of cyclohexane (99.0%) observed at 250 °C under pressure of 20 bar with Ru/ZSM-5 catalyst. Further the recyclability and stability have been checked and observed that Ru/ZSM-5 is stable up to 200 h and displayed excellence activity in both HDO and cyclohexane selectivity. Weight hourly space velocity (WHSV) was investigated (0.5–1.5 h−1). The suitable WHSV found for HDO of 2-methoxy phenol and cyclohexane yield was 1 h−1. The reaction mechanism showed that the Ru/ZSM-5 catalyst provoked the HDO compared to the others catalyst.

Catalytic performance of 2D-Mxene nano-sheets for the hydrodeoxygenation (HDO) of lignin-derived model compounds

2D Mxene nano-sheets (Ti3C2Tx) were investigated for the hydrodeoxygenation of guaiacol as a lignin-derived model compound. The catalyst was characterized by TEM, XPS, Raman spectroscopy and TPR. The acid-base properties were measured by TPD-NH3 and TPRe-MeOH. Phenol was the main product obtained, and methylanisole was observed as the second main product. The study of Anisole conversion shows that methylanisole was likely obtained by a bimolecular transalkylation. Such formation, which has only been reported over acid catalysts, was associated to the combined action of acid-base pairs identified.

Electrochemical Oxidation and Bond Cleavage of Lignin-Derived Model Compounds with Nanoparticle Catalysts

Electrochemistry offer an environmentally friendly approach to convert biomass or biomass derived material into valuable organic chemicals, petrochemical substitutes, and energy-intensive chemicals. Monomers could be generated by cleaving ether (C-O-C) linkages in lignin via thermal decomposition process such as reductive catalytic fraction (RCF). However, this process leaves behind a significant portion of soluble lignin oligomers with recalcitrant C-C linkages. Monomer yields from the RCF pathway are approaching theoretical limits based on ether bond cleavage. Therefore, with broader goal of improving lignin utilization within a biorefinery, we probed the electrocatalytic oxidation of model dimer compounds with C-C linkages representative of RCF oligomers. Electrochemical studies offer several advantages including operation at low temperatures and pressures, applied potentials can be used to control reaction rates and selectivities, and renewable electricity can be used, thus lowering overall greenhouse gas emissions. According to previous studies, several metals such as nickel, cobalt, copper, and platinum can be used to build electrocatalysts for biomass conversion. Therefore, we have synthesized a series of low-cost nickel and molybdenum nanoparticle catalysts for the electrocatalytic oxidation of model compounds. Besides the high surface and high stability advantages of supported nanoparticles in general, these candidates exhibit interesting catalytic activities resembling that of noble metal catalysts such as platinum in oxygen reduction reaction (ORR) which could also be beneficial in bond cleavage reactions in biomass or biomass derived material. The focus of this talk will be on the electrochemical studies of the selected nanoparticle catalysts toward C-C bond cleavage in RCF dimer model compounds. The results from the studies also lead to some insights we may be able to use to guide the future development of electro-oxidation of RCF oil/ biomass stream. Besides metallic, phosphide and carbide nanoparticles on carbon support, metal foils were also tested and were used as a comparison. Notably, a MoC catalyst on carbon support showed C-C and C-O bond cleavage activities in aqueous alcoholic solution with sodium hydroxide as the electrolyte.

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs < Pt/5HNbWO6/CNTs < Pt/20HNbMoO6/CNTs < Pt/20HNbWO6/CNTs < Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

Synthetic metabolic pathway for the production of 1-alkenes from lignin-derived molecules

BackgroundIntegration of synthetic metabolic pathways to catabolically diverse chassis provides new opportunities for sustainable production. One attractive scenario is the use of abundant waste material to produce a readily collectable product, which can reduce the production costs. Towards that end, we established a cellular platform for the production of semivolatile medium-chain α-olefins from lignin-derived molecules: we constructed 1-undecene synthesis pathway in Acinetobacter baylyi ADP1 using ferulate, a lignin-derived model compound, as the sole carbon source for both cell growth and product synthesis.ResultsIn order to overcome the toxicity of ferulate, we first applied adaptive laboratory evolution to A. baylyi ADP1, resulting in a highly ferulate-tolerant strain. The adapted strain exhibited robust growth in 100 mM ferulate while the growth of the wild type strain was completely inhibited. Next, we expressed two heterologous enzymes in the wild type strain to confer 1-undecene production from glucose: a fatty acid decarboxylase UndA from Pseudomonas putida, and a thioesterase ‘TesA from Escherichia coli. Finally, we constructed the 1-undecene synthesis pathway in the ferulate-tolerant strain. The engineered cells were able to produce biomass and 1-undecene solely from ferulate, and excreted the product directly to the culture headspace.ConclusionsIn this study, we employed a bacterium Acinetobacter baylyi ADP1 to integrate a natural aromatics degrading pathway to a synthetic production route, allowing the upgradation of lignin derived molecules to value-added products. We developed a highly ferulate-tolerant strain and established the biosynthesis of an industrially relevant chemical, 1-undecene, solely from the lignin-derived model compound. This study reports the production of alkenes from lignin derived molecules for the first time and demonstrates the potential of lignin as a sustainable resource in the bio-based synthesis of valuable products.

Catalytic hydrodeoxygenation of bio-oil using in situ generated hydrogen in plasma reactor: Effects of allumina supported catalysts and plasma parameters

Abstract In this study, hydrodeoxygenation of guaiacol, a lignin derived model compound, has been studied experimentally via a combination of dielectric barrier discharge plasma and catalyst. Cracking of methyl groups in the chemical structure of bio-oil is used to provide the hydrogen which is required for hydrodeoxygenation reaction. In order to maximize the degree of deoxygenation and guaiacol conversion, the effects of operating and plasma parameters including applied voltage, guaiacol and argon flow rate have been examined. Furthermore, performance of plasma alone and catalytic plasma has been compared by filling the active volume of the discharge with different commercial catalysts including Ni, Co–Mo, Ni–Mo, Pt–Re and Pt–Cl supported on Al2O3. The highest guaiacol conversion of 92% and deoxygenation degree of 65% are achieved in the presence of Pt–Cl/Al2O3 and Pt–Re/Al2O3 catalysts, respectively. According to the results, the main products were BTX, phenol, methylphenols and dimethylphenols. Unlike previous studies in which catechol was produced as a major product, in our plasma system phenol can be produced selectively through direct demethoxylation rather than demethylation reaction. It is also evident from the results that the hydrogen challenges of hydrodeoxygenation reaction can be overcome by catalytic DBD plasma reactor.

Catalytic hydrogenation and hydrodeoxygenation of lignin-derived model compound eugenol over Ru/C: Intrinsic microkinetics and transport phenomena

Heterogeneous catalytic hydrotreatment is recognized as a key valorization route of bio-based oxygenates in a bio-refinery concept. Catalytic hydrodeoxygenation (HDO) and hydrogenation of eugenol, a lignin building block model component, was investigated in silico and experimentally in a three-phase slurry reactor over the ruthenium supported on carbon (Ru/C) and by using hexadecane (HD) solvent. The influence of operating process conditions on the activity and selectivity of the transformations was determined; specifically, the temperature (225–325°C), hydrogen gas pressure (4–7MPa), catalyst loading (0–0.35wt%), eugenol loading (0–5wt%), process gas (H2 and N2), stirring speed (100–1000min−1) were varied within the listed values. Based on the detailed chromatographic, spectroscopic, microscopic, temperature-programed desorption, reduction, oxidation or physisorption analysis of solid, liquid and gas phase, a rather complex reaction-pathway network for eugenol hydrotreatment was proposed. Experimental results revealed that allyl group and benzene ring saturation was favored in comparison to competitive deoxygenation reactions, namely dehydroxylation and demethoxylation of oxygen moieties on aromatic ring. The mechanism of ketone group formation has been clarified among various proposed pathways in the literature, as it most likely proceeds via keto-enol isomerization. Precursors responsible for cyclohexane-ring contraction to substituted 5-member ring compounds were also identified and mechanism and kinetics of transformation was proposed. Intrinsic microkinetic modelling was based on the proposed network of parallel and consecutive homogeneous and catalytic reactions, and accounted the gas–liquid and liquid–solid mass transfer, adsorption and desorption kinetics and thermodynamic equilibria. Model results indicate 36- and 42-times higher demethoxylation and dehydroxylation rate constants for aromatics in comparison to corresponding oxygen-containing cycloalkanes.