Catalytic conversion of lignin pyrolysis model compound- guaiacol and its kinetic model including coke formation

Catalytic fast pyrolysis of waste pine sawdust over solid base, acid and base-acid tandem catalysts

Catalytic pyrolysis is an effective means for high-value utilization of biomass. This study investigated the effect of solid base catalysts (CaO, calcium aluminate catalysts CaAl-1, CaAl-2, CaAl-3), acid zeolite catalysts (ZSM-5, Fe/ZSM-5, Co/ZSM-5, Ni/ZSM-5, Cu/ZSM-5, Zn/ZSM-5) and base-acid tandem catalysts on pine sawdust pyrolysis using Py-GC/MS. Acid zeolite catalysts exhibited robust deoxidation and aromatization capabilities, favoring aromatics, while solid base catalysts yielded more phenols and ketones. Among the solid base catalysts, CaAl-3 (CaO-Ca12Al14O33) showed comparable deoxygenation activity to CaO and optimal aromatic selectivity with structural stability. Zn/ZSM-5 excelled in deoxygenation and aromatic selectivity (70.42%) among metal-modified ZSM-5 catalysts. Base-acid tandem catalysis promoted the formation of aliphatics and BTX (benzene, toluene, xylene) while suppressing polycyclic aromatics. The highest BTX content (44.35%) was achieved with CaO-Ca12Al14O33&Zn/ZSM-5 tandem catalysts in a 1:3 ratio. This work demonstrates base-acid tandem catalysis as a promising approach for converting pine sawdust into valuable chemicals.

Catalytic dehydration of glycerol over Cu-Fe-Al-based oxides: understanding changes in active sites throughout the reaction

The glycerol conversion into acetol using Fe, Al and Cu-based oxides was investigated. XRD results indicate the formation of nanosized particles with high phase dispersion, however, Raman, Mössbauer, 27Al NMR and XPS spectroscopies suggest the presence of iron(iii) oxide, Al2O3 and CuO phases. The FTIR with pyridine adsorption revealed high Lewis acidity. The TPR profile showed the reduction temperature range for the Fe3+ and Cu2+ sites, indicating the suitable condition for pretreatment. The N2 adsorption-desorption isotherms indicated the presence of micro-mesopores with interesting textural properties and specific area varying between 71 and 220 m2 g-1, while the porous morphology was observed by SEM and TEM images. The optimized catalytic tests showed glycerol conversion of 60% and acetol selectivity of 92% with 17% of coke according to TG profile. The recycling tests confirmed the efficiency of the solid, reaching 28% conversion and 91% acetol selectivity after four reuses and, after reactivation in an oxidizing atmosphere, the catalytic performance obtained results close to the second reuse. The interaction between the different Lewis acid sites involved in the mechanisms for the acetol and coke formation on the catalyst surface is discussed. The charge distribution represented by colors which indicates the acid-base surface was evaluated by a simple theoretical-computational study based on the DFT approach. The synergy between the active sites indicates that the presence of Cu0/Cu+ drastically increases the acetol selectivity which is a more important characteristic than the high Lewis acidity of Fen+ and Al3+.

Effects of Ni/Al2O3 catalyst treatment condition on thermocatalytic conversion of spent disposable wipes

Municipal solid waste (MSW) management is an essential municipal service. Proper waste treatment is an important part of the waste management. Thermocatalytic waste upcycling has recently gained great interest and attention as a method to extract value from waste, which potentially substitutes traditional waste treatment methods. This study aims at demonstrating the potential for thermocatalytic waste upcycling using spent disposable wipes as an MSW surrogate. Two different Ni/Al2O3 catalysts were prepared, treated under two different atmospheres (N2 and CO2). The catalyst treated in N2 (Ni/Al2O3-N2) exhibited a higher surface metallic Ni site than the catalyst treated in CO2 (Ni/Al2O3-CO2). The use of the Ni/Al2O3-N2 increased the yield of gas pyrolysate and decreased the yield of byproduct (e.g., wax), compared with no catalyst and the Ni/Al2O3-CO2. In particular, the Ni/Al2O3-N2 catalyst affected the generation of gaseous hydrogen (H2) by increasing the H2 yield by up to 102% in comparison with the other thermocatalytic systems. The highest H2 yield obtained with the Ni/Al2O3-N2 was attributed to the most surface metallic Ni sites. However, the Ni/Al2O3-N2 catalyst led to char having a lower higher heating value than the other catalysts due to its lowest carbon content. The results indicated that the reduction treatment environment for Ni/Al2O3 catalyst influences thermocatalytic conversion product yields of spent disposable wipes, including enhanced H2 production.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s11814-023-1461-8.

Evidence of a Phenolic Pool as a Key Intermediate for Zeolite-Catalyzed Lignin Pyrolysis

The phenolic pool is considered to be an important intermediate during the catalytic conversion of biomass. However, no direct evidence has been reported on its full picture on a molecular level due to the huge challenges in probing the reactive and lowly volatile phenolic oligomers with state-of-the-art technologies. Herein, we report the online detection and structural identification of a phenolic pool by utilizing in-situ atmospheric-pressure photoionization mass spectrometry, demonstrating that the phenolic pool is formed through repolymerization of monomers with an equidistant group pattern and acts as a key mechanistic step for both valuable aromatic products and undesired coke. The exploration of the real reactive species is also of great importance for the rational design and synthesis of advanced catalysts with high activity.

Facile Electrochemical Demethylation of 2-Methoxyphenol to Surface-Confined Catechol on the MWCNT and Its Efficient Electrocatalytic Hydrazine Oxidation and Sensing Applications

Owing to its biological significance, preparation of stable surface-confined catechol (CA) is a long-standing interest in electrochemistry and surface chemistry. In this connection, various chemical approaches such as covalent immobilization (using amine- and carboxylate-functionalized CA, diazotization-based coupling, and Michael addition reaction), self-assembled monolayer on gold (thiol-functionalized CA is assembled on the gold surface), CA adsorption on the ad-layer of a defect-free single-crystal Pt surface, π-π bonding, CA pendant metal complexes, and CA-functionalized polymer-modified electrodes have been reported in the literature. In general, these conventional methods are involved with a series of time-consuming synthetic procedures. Indeed, the preparation of a surface-fouling-free surface-confined system is a challenging task. Herein, we introduce a new and facile approach based on electrochemical demethylation of 2-methoxyphenol as a precursor on the graphitic surface (MWCNT) at a bias potential, 0.5 V vs Ag/AgCl in neutral pH solution. Such an electrochemical performance resulted in the development of a stable and well-defined redox peak at E ^o' = 0.15 (A2/C2) V vs Ag/AgCl within 10 min of preparation time in pH 7 phosphate buffer solution. Calculated surface excess (16.65 × 10^-9 mol cm^-2) is about 10-1000 times higher than the values reported with other preparation methods. The product (catechol) formed on the modified electrode was confirmed by collective electrochemical and physicochemical characterizations such as potential segment analysis, TEM, Raman, IR, UV-vis, GC-MS, and NMR spectroscopic techniques, and thin-layer chromatographic studies. The electrocatalytic efficiency of the surface-confined CA system was demonstrated by studying hydrazine oxidation and sensing reactions in a neutral pH solution. This new system is found to be tolerant to various interfering biochemicals such as uric acid, xanthine, hypoxanthine, glucose, nitrate, hydrogen peroxide, ascorbic acid, Cu²⁺, and Fe²⁺. Since the approach is simple, rapid, and reproducible, a variety of surface-confined CA systems can be prepared.

Molecular simulations of palladium catalysed hydrodeoxygenation of 2-hydroxybenzaldehyde using density functional theory

The catalytic conversion of 2-hydroxybenzaldehyde (2-HB) is carried out numerically over a Pd(111) surface using density functional theory. The palladium catalyst surface is designed using a 12 atom monolayer and verified with the adsorption of phenol, benzene, anisole, guaiacol, and vanillin; it is found that the adsorption energies along with the adsorption configurations of phenol and benzene are in excellent agreement with the literature. The conversion of 2-HB over the Pd(111) catalyst surface is performed using four reaction schemes: (i) dehydrogenation of the formyl group followed by elimination of CO and association of hydrogen with 2-hydroxyphenyl to produce phenol, (ii) direct elimination of CHO from 2-HB followed by elimination of hydrogen from adsorbed CHO and association of hydrogen with 2-hydroxyphenyl to produce phenol, (iii) direct dehydroxylation of 2-HB followed by association of a hydrogen atom with 2-formylphenyl to produce benzaldehyde, and (iv) dehydrogenation of the hydroxyl group of 2-HB followed by elimination of an oxygen atom and association of a hydrogen atom with 2-formylphenyl to produce benzaldehyde. Along with the reaction mechanisms and their barrier heights, all reaction steps are considered for kinetic modelling in the temperature range 498-698 K with 50 K intervals. The rate constants, pre-exponential factors, and equilibrium constants of all elementary reaction steps are evaluated for each temperature. Kinetic analyses of the catalytic conversion of 2-HB over the Pd(111) surface suggests the production of phenol as an intermediate, instead of benzaldehyde, via dehydrogenation of the formyl group of 2-HB as a first elementary reaction step because of its low activation barrier and the high rate constant of the rate controlling step. Furthermore, the equilibrium constants of the rate controlling step in the production of phenol from 2-HB over the Pd(111) surface report a major fraction of the product in the product mixture even at a low temperature of 498 K.

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity and yield unsatisfactory conversion. Understanding the pyrolysis reaction mechanism at the molecular level may help to make this sustainable process more economic. Reactive intermediates are responsible for product branching and hold the key to unveiling these mechanisms, but are notoriously difficult to detect isomer-selectively. Here, we investigate the catalytic pyrolysis of guaiacol, a lignin model compound, using photoelectron photoion coincidence spectroscopy with synchrotron radiation, which allows for isomer-selective detection of reactive intermediates. In combination with ambient pressure pyrolysis, we identify fulvenone as the central reactive intermediate, generated by catalytic demethylation to catechol and subsequent dehydration. The fulvenone ketene is responsible for the phenol formation. This technique may open unique opportunities for isomer-resolved probing in catalysis, and holds the potential for achieving a mechanistic understanding of complex, real-life catalytic processes.

The conversion of lignin by catalytic fast pyrolysis into useful fine chemicals is a promising route to fuel production, however selectivity and conversion are still not optimal. Here, the authors investigate the reaction mechanism by detection of reactive intermediates responsible for the formation of key products.