Isopropanol decomposition on carbon based acid and basic catalysts

Activated carbon from almond shells using an eco-compatible method: screening, optimization, characterization, and adsorption performance testing

Activated carbon as a low-cost adsorbent prepared from almond shells using H3PO4 as a chemical activator and room vacuum pyrolysis as a physical activator, which is considered to be an eco-compatible preparation process. Experimental design methodology was used to study and optimize the effects of eight preparation parameters on I2 adsorption expressed by the iodine index (mg g-1). It was found that optimum activated carbon was obtained by chemical activation with H3PO4 at first, followed by physical treatment at 420 °C under a vacuum pressure of -0.8 bar. The obtained activated carbon was characterized by a thermogravimetric analyzer, scanning electron microscopy coupled to EDX, X-ray diffraction, and Fourier transform infrared absorption spectroscopy. The zero-charge pH and the characteristics of surface chemistry by Boehm titration were determined to predict the acid-base properties of the prepared material. An adsorption efficiency study of crystal violet dye on the optimally produced activated carbon was carried out. The obtained results of physicochemical characterization showed interesting properties of our activated carbon in comparison with those produced by other methods. Among these properties, an important porous surface, high thermal stability, and a disorganized graphitic crystalline structure were revealed. In addition to the carbon and oxygen elements, EDX analysis revealed the presence of phosphorus element, and the FTIR analysis indicated the existence of phosphonate groups and an acidic character, which resulted from chemical activation by H3PO4. An iodine index of 824.85 mg g-1 was achieved for optimal preparation. Crystal violet adsorption studies show a pseudo-first-order kinetic process and fit well with the Freundlich isotherm model, and thus, the predicted adsorption capacity was 364.27 mg g-1.

Advanced Material-oriented Biomass Precise Reconstruction: A Review on Porous Carbon with Inherited Natural Structure and Created Artificial Structure by Post-treatment

Manufacturing of porous carbon with biomass resources has been intensively investigated in recent decades. The diversity of biomass species and great variety of processing methods enable the structural richness of porous carbon as well as their wide applications. In this review, we specifically focused on the structure of biomass-derived porous carbon either inherited from natural biomass or created by post-treatment. The intrinsic structure of plant biomass was briefly introduced and the utilization of the unique structures at different length-scales were discussed. In term of post-treatment, the structural features of activated carbon by traditional physical and chemical activation were summarized and compared in a wide spectrum of biomass species, statistical analysis were performed to evaluate the effectiveness of different activation methods in creating specific pore structures. The similar pore structure of biomass-derived carbon and coal-derived carbon suggested a promising replacement with more sustainable biomass resources in producing porous carbon. In summary, using biomass as porous carbon precursor endows the flexibility of using its naturally patterned micro-structure and the tunability of controlled pore-creation by post treatment. This article is protected by copyright. All rights reserved.

Total Oxidation of Isopropanol in the Liquid Phase, under Atmospheric Pressure and Low Temperature, on Transition Metal Oxides Catalysts Cr2O3 and Fe2O3

Isopropanol oxidation in the liquid phase under atmospheric pressure and low temperature has been studied in the presence of transition metal oxides (Cr2O3 and Fe2O3) prepared by the precipitation method. These solids characterized by structural analyses (FTIR and XRD) and textural analysis (BET) have led to results in line with those reported in the literature. Chromium oxide has a much more developed texture, with a specific surface area and pore volume 5 times larger than iron oxide. Both of the solids show a good specific activity and led to acetone and carbon dioxide to be formed as the only oxidation products of isopropanol. However, chromium oxide is more active. The initial catalytic activity for the latter is varying between 4.87 ∗ 10−6 and 5.79 ∗ 10−6 mol·g−1·s−1 with temperature range from 40 to 80°C. Kinetic study shows that the reaction follows a successive scheme: isopropanol ⟶ acetone ⟶ CO2 involving a redox mechanism. The low value of the activation apparent energy (Ea.(Cr2O3) = 2.87 kJ·mol−1 < Ea. (Fe2O3) = 5.37 kJ·mol−1) justifies the relatively higher activity observed for chromium oxide.

Insights into the promotion role of phosphorus doping on carbon as a metal-free catalyst for low-temperature selective catalytic reduction of NO with NH3

The catalytic reduction of NO with NH₃ (NH₃-SCR) on phosphorus-doped carbon aerogels (P-CAs) was studied in the temperature range of 100–200 °C. The P-CAs were prepared by a one-pot sol–gel method by using phosphoric acid as a phosphorus source followed by carbonization at 600–900 °C. A correlation between catalytic activity and surface P content is observed. The P-CA-800_vac sample obtained via carbonization at 800 °C and vacuum treatment at 380 °C shows the highest NO conversion of 45.6–76.8% at 100–200 °C under a gas hourly space velocity of 500 h⁻¹ for the inlet gas mixture of 500 ppm NO, 500 ppm NH₃ and 5.0 vol% O₂. The coexistence of NH₃ and O₂ is essential for the high conversion of NO on the P-CA carbon catalysts, which can decrease the spillover of NO₂ and N₂O. The main Brønsted acid sites derived from P-doping and contributed by the C–OH group at edges of carbon sheets are beneficial for NH₃ adsorption. In addition, the C₃–P Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O configuration seems to have the most active sites for favorable adsorption and dissociation of O₂ and facilitates the formation of NO₂. Therefore, the simultaneous presence of acidic groups for NH₃ adsorption and the C₃–PO active sites for NO₂ generation due to the activation of O₂ molecules is likely responsible for the significant increase in the NH₃-SCR activity over the P–CAs. The transformation of C₃–PO to C–O–P functional groups after the reaction is found, which could be assigned to the oxidation of C₃–PO by the dissociated O*, resulting in an apparent decrease of catalytic activity for P-CAs. The C–O–P based functional groups are also active in the NH₃-SCR reaction.

P species can effectively enhance the catalytic activity of carbon aerogels for NO reduction at low temperature.

Acid Mesoporous Carbon Monoliths from Lignocellulosic Biomass Waste for Methanol Dehydration

Activated carbon monoliths (ACMs), with 25 cells/cm², were prepared from the direct extrusion of Alcell, Kraft lignin and olives stones particles that were impregnated with phosphoric acid, followed by activation at 700 °C. These ACMs were used as catalysts for methanol dehydration reaction under air atmosphere. ACM that was prepared from olive stone and at impregnation ratio of 2, OS2, showed the highest catalytic activity, with a methanol conversion of 75%, a selectivity to dimethyl ether (DME) higher than 90%, and a great stability under the operating conditions studied. The results suggest that the monolithic conformation, with a density channel of 25 cells/cm² avoid the blockage of active sites by coke deposition to a large extent. Methanol conversion for OS2 was reduced to 29% in the presence of 8%v water, at 350 °C, although the selectivity to DME remained higher than 86%. A kinetic model of methanol dehydration in the presence of air was developed, while taking into account the competitive adsorption of water. A Langmuir-Hinshelwood mechanism, whose rate-limiting step was the surface reaction between two adsorbed methanol molecules, represented the experimental data under the conditions studied very well. An activation energy value of 92 kJ/mol for methanol dehydration reaction and adsorption enthalpies for methanol and water of −12 and −35 kJ/mol, respectively, were obtained.

Novel Polymer–Silica Composite-Based Bifunctional Catalysts for Hydrodeoxygenation of 4-(2-Furyl)-3-Buten-2-One as Model Substance for Furfural–Acetone Aldol Condensation Products

Novel bifunctional metal-loaded polymer–silica composite (PSC) catalysts were investigated in the hydrodeoxygenation (HDO) of 4-(2-furyl)-3-buten-2-one (FAc) as a model substance for furfural–acetone aldol condensation products. PSC catalysts were synthesized via a sol–gel method with different polymer contents and subsequently doped with different noble metals. The product composition of the HDO of FAc could be tuned by using catalysts with different polymer (i.e., acidic properties) and metal content (i.e., redox properties), showing the great potential of metal-loaded PSC materials as tunable catalysts in biomass conversions with complex reaction networks. Furthermore, high yields (>90%) of the fully hydrodeoxygenated product (n-octane) could be obtained using noble metal-loaded PSC catalysts in only 8 h of reaction time.

Catalytic efficiency of activated carbon functionalized with phosphorus-containing groups in 2-propanol dehydration

The functionalization of activated carbon (AC) by P-containing groups was conducted, and their thermal desorption was studied. Depending on the used method, the functionalized AC contains 0.5–1.45 mmol/g of acidic groups acting in catalytic 2-propanol dehydration. All catalysts showed 100% conversion of 2-propanol to propylene. The catalytic activity does not change with time under isothermal conditions and during their repeated use in catalysis, for 3 cycles of heating-cooling. In fact, the yield of propylene remains stable; it does not decrease with each cycle. Preliminary oxidation with nitric acid causes a small increase in the catalytic activity.

Functionalised heterogeneous catalysts for sustainable biomass valorisation

Functionalised heterogeneous catalysts show great potentials for efficient valorisation of renewable biomass to value-added chemicals and high-energy density fuels.