Hydrodeoxygenation of a bio-oil model compound derived from woody biomass using spray-pyrolysis-derived spherical γ-Al2O3-SiO2 catalysts

Effect of microwave pretreatment on pyrolysis of chili straw: thermodynamics, activation energy, and solid reaction mechanism

In this work, chili straw (CS) was pretreated by microwave at 250 W, 406 W, 567 W, and 700 W. The pyrolysis characteristics, kinetics, thermodynamic parameters, and solid reaction mechanism were investigated. The maximum weight loss rate increases from  - 24.72%/°C at P0 to  - 28.01%/°C at P700 after microwave pretreatment, and the residual mass decreases from 31.81 at P0 to 26.71% at P700. In addition, microwave pretreatment leads to a decrease in activation energy, ∆H, and ∆G at the end of the pyrolysis (α > 0.7). The solid reaction mechanism of CS pyrolysis is revealed by the Z-master plots method, with un-pretreated CS conforming to P2, D4, F3/2, and F3, respectively. Microwave pretreatment changes the solid reaction mechanism mainly in the third stage, when α = 0.8, the mechanism function changes from f(α) = (1 - α)3 at P0 to f(α) = (1 - α) at P700, and the number of reaction order is reduced, which is profitable for CS pyrolysis.

Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

Production of aromatic hydrocarbons from lignin derivatives by catalytic cracking over a SiO2–Al2O3 catalyst†

Catalytic cracking of phenolic compounds to aromatic hydrocarbons is vital to the utilization of lignin. In this work, pristine amorphous SiO₂–Al₂O₃ was used as a catalyst to produce aromatic hydrocarbons from lignin-derived phenolics by catalytic cracking using methanol as the solvent. These catalysts were characterized by various techniques (XRD, NH₃-TPD, Py-IR, etc.) and evaluated on a fixed bed reactor using guaiacol as a model compound. The effects of reaction temperature, the flow of carrier gas, the molar ratio of guaiacol to methanol, and WHSV were investigated. 33-SA (SiO₂–Al₂O₃ with the SiO₂ content of 33%) exhibited the best catalytic activity due to its high content of Lewis acid sites (168.47 μmol g⁻¹). Co-feeding with methanol promoted the removal of oxygen atoms and improved the reaction system H/C_eff. Under the optimal conditions of 400 °C, 25 mL min⁻¹ N₂, a molar ratio of methanol to guaiacol of 25, and WHSV of 8/3 h⁻¹, the yield of aromatic hydrocarbons reached 57.93%. The deactivating species in the transformation of guaiacol into aromatic hydrocarbons on catalysts were also studied.

Catalytic cracking of phenolic compounds to aromatic hydrocarbons is vital to the utilization of lignin.

Mechanistic Insight Into the Application of Alumina-Supported Pd Catalysts for the Hydrogenation of Nitrobenzene to Aniline

Two Pd/γ-Al₂O₃ catalysts are examined for the vapor phase hydrogenation of nitrobenzene over the temperature range of 60–200 °C. A 1 wt % catalyst is selected as a reference material that is diluted with γ-alumina to produce a 0.3 wt % sample, which is representative of a metal loading linked to a candidate industrial specification aniline synthesis catalyst. Cyclohexanone oxime is identified as a by-product that is associated with reagent transformation. Temperature-programed infrared spectroscopy and temperature-programed desorption measurements of chemisorbed CO provide information on the morphology of the crystallites of the higher Pd loading catalyst. The lower Pd loading sample exhibits a higher aniline selectivity by virtue of minimization of product overhydrogenation. Reaction testing measurements that were undertaken employing elevated hydrogen flow rates lead to the proposition of separate reagent and product-derived by-product formation pathways, each of which occurs in a consecutive manner. A global reaction scheme is proposed that defines the by-product distribution accessible by the grades of catalyst examined. This information is helpful in defining product purification procedures that would be required in certain heat recovery scenarios connected with large-scale aniline production.

Spray pyrolysis synthesis and UV-driven photocatalytic activity of mesoporous Al2O3@TiO2 microspheres

Mesoporous microspheres of Al₂O₃@TiO₂ were effe ctively and rapidly prepared by the sol-spray pyrolysis (SP) method. Ultrasonic-induced droplets containing titania sol, boehmite sol, and citric acid (CA) were pyrolyzed to γ-Al₂O₃-incorporated anatase TiO₂ microspheres. The SP-derived Al₂O₃@TiO₂ microspheres exhibited higher porosity and lower bandgap energy than pure TiO₂ and commercial P25. The TiO₂ microspheres incorporated with 5 wt% amorphous γ-Al₂O₃ efficiently removed tetracycline (TC) after 60 min of pre-adsorption and 140 minutes of UV illumination (removal efficiency ~ 91%, surpassing those of pure TiO₂ and commercial P25). Introducing amorphous γ-Al₂O₃ into the anatase TiO₂ matrix created a synergetic effect that enhanced the accumulation of TC onto the catalyst surface; meanwhile, the formation of defective heterojunctions favored the separation and immigration of the photo-generated holes and electrons. In a reaction mechanism analysis, h⁺ and O₂^•‾ radicals were identified as the main instigators of TC photooxidation. Furthermore, the SP-derived Al₂O₃@TiO₂ microspheres demonstrated good stability and renewability in durability tests. The study provides a simple and scalable method for manufacturing Al₂O₃-decorated TiO₂ microspheres with improved adsorption and photocatalytic performance.

Microwave-Assisted Pyrolysis of Biomass with and without Use of Catalyst in a Fluidised Bed Reactor: A Review

Lignocellulosic biomass and waste, such as plastics, represent an abundant resource today, and they can be converted thermo-chemically into energy in a refinery. Existing research works on catalytic and non-catalytic pyrolysis performed in thermally-heated reactors have been reviewed in this text, along with those performed in microwave-heated ones. Thermally-heated reactors, albeit being the most commonly used, present various drawbacks such as superficial heating, high thermal inertia and slow response times. That is why microwave-assisted pyrolysis (MAP) appears to be a very promising technology, even if the process does present some technical drawbacks as well such as the formation of hot spots. The different types of catalysts used during the process and their impacts have also been examined in the text. More specifically, studies conducted in fluidised bed reactors (FBR) have been detailed and their advantages and drawbacks discussed. Finally, future prospects of MAP have been briefly presented.

Effect of eggshell- and homo-type Ni/Al2O3 catalysts on the pyrolysis of food waste under CO2 atmosphere

This study highlights the potential of pyrolysis of food waste (FW) with Ni-based catalysts under CO₂ atmosphere as an environmentally benign disposal technique. FW was pyrolyzed with homo-type Ni/Al₂O₃ (Ni-HO) or eggshell-type Ni/Al₂O₃ (Ni-EG) catalysts under flowing CO₂ (50 mL/min) at temperatures from 500 to 700 °C for 1 h. A higher gas yield (42.05 wt%) and a lower condensable yield (36.28 wt%) were achieved for catalytic pyrolysis with Ni-EG than with Ni-HO (34.94 wt% and 40.06 wt%, respectively). In particular, the maximum volumetric content of H₂ (21.48%) and CO (28.43%) and the lowest content of C₂-C₄ (19.22%) were obtained using the Ni-EG. The formation of cyclic species (e.g., benzene derivatives) in bio-oil was also effectively suppressed (24.87%) when the Ni-EG catalyst and CO₂ medium were concurrently utilized for the FW pyrolysis. Accordingly, the simultaneous use of the Ni-EG catalyst and CO₂ contributed to altering the carbon distribution of the pyrolytic products from condensable species to value-added gaseous products by facilitating ring-opening reactions and free radical mechanisms. This study should suggest that CO₂-assisted catalytic pyrolysis over the Ni-EG catalyst would be an eco-friendly and sustainable strategy for disposal of FW which also provides a clean and high-quality source of energy.