Sorption and Textural Properties of Activated Carbon Derived from Charred Beech Wood

The aim of this study was to prepare activated carbon materials with different porous structures. For this purpose, the biomass precursor, beech wood, was carbonized in an inert atmosphere, and the obtained charcoal was physically activated using carbon dioxide at 1273 K. Different porous structures were obtained by controlling the time of the activation process. Prepared materials were characterized in terms of textural (N2 sorption at 77 K), structural (XRD), and sorption properties (CO2, C2H4, C4H10). The shortest activation time resulted in a mostly microporous structure, which provided a high sorption of CO2. Increasing the activation time led to an increasing of the pores’ diameters. Therefore, the highest ethene uptake was obtained for the material with an intermediate activation time, while the highest butane uptake was obtained for the material with the highest activation time.

Dehydration of Fructose to 5-Hydroxymethylfurfural: Effects of Acidity and Porosity of Different Catalysts in the Conversion, Selectivity, and Yield

There is a demand for renewable resources, such as biomass, to produce compounds considered as platform molecules. This study deals with dehydration of fructose for the formation of 5-hydroxymethylfurfural (HMF), a feedstock molecule. Different catalysts (aluminosilicates, niobic acid, 12-tungstophosphoric acid—HPW, and supported HPW/Niobia) were studied for this reaction in an aqueous medium. The catalysts were characterized by XRD, FT-IR, N2 sorption at −196 °C and pyridine adsorption. It was evident that the nature of the sites (Brønsted and Lewis), strength, quantity and accessibility to the acidic sites are critical to the conversion and yield results. A synergic effect of acidity and mesoporous area are key factors affecting the activity and selectivity of the solid acids. Niobic acid (Nb2O5·nH2O) revealed the best efficiency (highest TON, yield, selectivity and conversion). It was determined that the optimum acidity strength of catalysts should be between 80 to 100 kJ mol−1, with about 0.20 to 0.30 mmol g−1 of acid sites, density about 1 site nm−2 and mesoporous area about 100 m2 g−1. These values fit well within the general order of the observed selectivity (i.e., Nb2O5 > HZSM-5 > 20%HPW/Nb2O5 > SiO2-Al2O3 > HY > HBEA).

Vanadia–Zirconia and Vanadia–Hafnia Catalysts for Utilization of Volatile Organic Compound Emissions

Utilization is a sustainable and interesting alternative for the destructive treatment of volatile organic compounds due to avoided CO2 emission. This work concentrates on the development of active and sulfur-tolerant catalysts for the utilization of contaminated methanol. Impregnated and sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were thoroughly characterized by N2 sorption, analytical (S)TEM, elemental analysis, XRD and Raman spectroscopy, and their performances were evaluated in formaldehyde production from methanol and methanethiol mixture. The results showed higher activity of the sol–gel prepared catalysts due to formation of mono- and polymeric vanadia species. Unfortunately, the most active vanadia sites were deactivated more easily than the metal-mixed oxide HfV2O7 and ZrV2O7 phases, as well as crystalline V2O5 observed in the impregnated catalysts. Metal-mixed oxide phases were formed in impregnated catalysts through formation of defects in HfO2 and ZrO2 structure during calcination at 600 °C, which was evidenced by Raman spectroscopy. The sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were able to produce formaldehyde from contaminated methanol with high selectivity at temperature around 400 °C, while impregnated catalysts required 50–100 °C higher temperatures.

Towards Sustainability Pathway with Bio-Derived Platinum and Palladium Catalyst for Furfural Hydrogenation—A Novel Greener Approach in Catalysis

The use of living plants to recover precious metals with potential catalytic activity is still at the infant stage. In this study, selective hydrogenation of furfural to furfuryl alcohol using novel bio-ore catalysts recovered from the end stage of phytomining process is demonstrated. The phytomining process was carried out in the green house by artificially contaminating cassava (Manihot esculenta) plant with 500 mg/L palladium (Pd) and platinum (Pt) solutions for a period of eight weeks. After harvesting, concentrations of metals as high as 78 ± 0.047 and 1276 ± 0.036 µg/g of Pd and Pt, respectively, were detected in the calcinated root of cassava. The produced bio-ore catalysts; @PdCassCat and @PtCassCat were fully characterized with the following techniques: transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), powder X-ray diffraction (pXRD), N2-sorption, and UV-visible spectroscopy techniques and directly applied as catalysts for hydrogenation of furfural to furfuryl alcohol. The reaction was conducted under an optimized condition (furfural (10 mmol), triethylamine (Et3N) (10 mmol), formic acid (20 mmol), temperature (160 °C), catalyst amount (40 mg)) realizing a yield of 76.5% and 100% furfuryl alcohol using @PdCassCat and @PtCassCat, respectively. The catalytic activities of the @PdCassCat and @PtCassCat were excellent as well as recyclable up to four and five times, respectively.

Evaluation of Coal Pore Connectivity Using N2 Sorption Isotherm and Spontaneous Imbibition Tests

Pore structure and connectivity of coal are critical factors in coal gas migration and production, which can be characterized by studying the kinetics of capillary imbibition behaviour within the pore spaces. In order to investigate them, six typical coal samples from different collieries in China (Yangcun, Changcun, Gengcun, Yanbei, Dongxia, and Yuwu coal) are selected to carry out N2 sorption isotherm and spontaneous imbibition tests. Results from N2 sorption isotherm tests show that there is a great difference between the total specific surface area and total pore volume among the six coal samples. Their total specific surface area varies from 0.302 to 3.275 m2/g, and the total pore volume varies from 1.782 to 10.94 mm3/g. The pore volume relationship of coal sample among them is in order from the large to small: Dongxia>Yangcun>Gengcun>Yuwu>Changcun>Yanbei coal, and the specific surface area is in order from the large to small: Yangcun>Dongxia>Changcun>Yuwu>Gengcun>Yanbei coal. The imbibition characters of six coal samples were matched using explicit the short-time limit t ⟶ 0 and long-time limit t ⟶ ∞ models by Zhmud et al., respectively. The results show that the long-time limit t ⟶ ∞ model is better. Combined with pore structure analysis, it can be qualitatively analyzed that the imbibition capacity of six coal samples is positively correlated with the connectivity of coal pores, which is ranked as Changcun>Yanbei>Gengcun>Yangcun>Dongxia>Yuwu coal. This work will help understand the mechanism controlling fluid loss and ultimate gas/oil recovery in unconventional hydrocarbon exploration.

Effects of Reaction Temperature on the Photocatalytic Activity of TiO2 with Pd and Cu Cocatalysts

The aim of this study was to investigate the effects of reaction temperature on the photocatalytic activity of TiO2 with Pd and Cu cocatalysts. N2 sorption, transmission electron microscopy and high-resolution transmission electron microscopy were used to characterize the specific surface area, pore volume, pore size, morphology and metal distribution of the catalysts. The photocatalytic destruction of methylene blue under UV light irradiation was used to test its activity. The concentration of methylene blue in water was determined by UV-vis spectrophotometer. Pd/TiO2 catalyst was more active than Cu/TiO2 and TiO2. At 0–50 °C reaction temperature, the activity of TiO2 and Pd/TiO2 increased with an increase of reaction temperature. When the temperature was as high as 70 °C, the reaction rate of TiO2 drop slightly and Pd/TiO2 became less effective. In contrast, Cu/TiO2 was more active at room temperature than the other temperatures. The results indicate that the photocatalytic activity of the catalyst is influenced by the reaction temperature and the type of cocatalyst. When the reaction temperature is higher than 70 °C, the recombination of charge carriers will increase. The temperature range of 50–80 °C is regarded as the ideal temperature for effective photolysis of organic matter. The effects of reaction temperature mainly influence quantum effect, i.e., electron-hole separation and recombination.

CO2/N2 Separation Properties of Polyimide-Based Mixed-Matrix Membranes Comprising UiO-66 with Various Functionalities

Nanocrystalline UiO-66 and its derivatives (containing -NH2, -Br, -(OH)2) were developed via pre-synthetic functionalization and incorporated into a polyimide membrane to develop a mixed-matrix membrane (MMM) for CO2/N2 separation. Incorporation of the non-functionalized UiO-66 nanocrystals into the polyimide membrane successfully improved CO2 permeability, with a slight decrease in CO2/N2 selectivity, owing to its large accessible surface area. The addition of other functional groups further improved the CO2/N2 selectivity of the polymeric membrane, with UiO-66-NH2, UiO-66-Br, and UiO-66-(OH)2 demonstrating improvements of 12%, 4%, and 17%, respectively. Further evaluation by solubility–diffusivity analysis revealed that the functionalized UiO-66 in MMMs can effectively increase CO2 diffusivity while suppressing N2 sorption, thus, resulting in improved CO2/N2 selectivity. Such results imply that the structural tuning of UiO-66 by the incorporation of various functional groups is an effective strategy to improve the CO2 separation performance of MMMs.

Generalized Methodology for Inserting Metal Heteroatoms into the Layered Zeolite Precursor RUB-36 by Interlayer Expansion

The incorporation of metal heteroatoms into zeolites is an effective modification strategy for enhancing their catalytic performance. Herein, for the first time we report a generalized methodology for inserting metal heteroatoms (such as Sn, Fe, Zn, and Co) into the layered zeolite precursor RUB-36 via interlayer expansion by using the corresponding metal acetylacetate salt. Through this generalized methodology, Sn-JHP-1, Fe-JHP-1, Zn-JHP-1 and Co-JHP-1 zeolites could be successfully prepared by the reaction of RUB-36 and corresponding metal acetylacetate salt at 180 °C for 24 h in the presence of HCl solution. As a typical example, Sn-JHP-1 and calcined Sn-JHP-1 (Sn-JHP-2) zeolite is well characterized by the X-ray diffraction (XRD), diffuse reflectance ultraviolet-visible (UV-Vis), inductively coupled plasma (ICP), N2 sorption, temperature-programmed-desorption of ammonia (NH3-TPD) and X-ray photoelectron spectroscopy (XPS) techniques, which confirm the expansion of adjacent interlayers and thus the incorporation of isolated Sn sites within the zeolite structure. Notably, the obtained Sn-JHP-2 zeolite sample shows enhanced catalytic performance in the conversion of glucose to levulinic acid (LA) reaction.

MCM-22, MCM-36, and ITQ-2 Zeolites with Different Si/Al Molar Ratios as Effective Catalysts of Methanol and Ethanol Dehydration

MCM-22, MCM-36, and ITQ-2 zeolites with the intended Si/Al molar ratios of 15, 25, and 50 were synthetized and tested as catalysts for dehydration of methanol to dimethyl ether and dehydration of ethanol to diethyl ether and ethylene. The surface concentration of acid sites was regulated by the synthesis of zeolite precursors with different aluminum content in the zeolite framework, while the influence of porous structure on the overall efficiency of alcohol conversion was analyzed by application of zeolitic materials with different types of porosity—microporous MCM-22 as well as microporous-mesoporous MCM-36 and ITQ-2. The zeolitic samples were characterized with respect to their: chemical composition (ICP-OES), structure (XRD, FT-IR), texture (N2 sorption), and surface acidity (NH3-TPD). Comparison of the catalytic activity of the studied zeolitic catalysts with other reported catalytic systems, including zeolites with the similar Si/Al ratio as well as γ-Al2O3 (one of the commercial catalysts for methanol dehydration), shows a great potential of MCM-22, MCM-36, and ITQ-2 in the reactions of alcohols dehydration.

Room-Temperature Nitrophenol Reduction over Ag–CeO2 Catalysts: The Role of Catalyst Preparation Method

Ag–CeO2 catalysts (20 mol % Ag) were synthesized using different techniques (co-precipitation, impregnation, and impregnation of pre-reduced ceria), characterized by XRD, N2 sorption, TEM, H2-TPR methods, and probed in room-temperature p-nitrophenol reduction into p-aminophenol in aqueous solution at atmospheric pressure. The catalyst preparation method was found to determine the textural characteristics, the oxidation state and distribution of silver and, hence, the catalytic activity in the p-nitrophenol reduction. The impregnation technique was the most favorable for the formation over the ceria surface of highly dispersed silver species that are active in the p-nitrophenol reduction (the first-order rate constant k = 0.656 min−1).