Search Results (22)

The catalytic conversion of carbon dioxide to methanol is significantly important both practically and scientifically for the reduction in CO₂ emissions. Furthermore, it can partially address the issue of human reliance on non-renewable resources. The main motivation of this study is to use a melamine polymer network to support a copper-based catalyst for CO₂ hydrogenation to methanol. Based on Schiff base chemistry, a facile catalyst-free process, a novel porous polyaminal polymer (MGPN) was prepared with nitrogen contents as high as 38%. MGPN was used as a support for Cu-based catalyst and applied in CO₂ hydrogenation to CH₃OH under mild conditions. A deep characterization of the MGPN@CuO/ZnO/Al₂O₃ catalyst was made through FTIR, N₂ adsorption–desorption, SEM-EDS, TEM, TGA, XRD, CO₂-TPD, and H₂-TPR techniques. The CO₂ hydrogenation study was performed in a fixed bed reactor with a residence time of 1.104 s on varying parameters such as the metal loading, catalyst amount, flow rate, pressure, calcination temperatures, reduction temperatures, and catalytic reaction temperature profile. The space-time yield (STY) of 145.43 mg_methanol·g_catalyst⁻¹·h⁻¹, a selectivity of 98.36%, and CO₂ conversion of 11.76% were obtained under an economically and energetically sustainable low-pressure (1 MPa) and 260 °C hydrogenation process. Full article

Activated biocarbons were synthesized from avocado seeds using potassium carbonate as an activating agent. The study aimed to evaluate K₂CO₃ as a greener and less corrosive alternative to KOH, traditionally used for producing porous carbons. Twelve samples were obtained under varying activation conditions using both dry K₂CO₃ and its saturated solution. The material activated at 800 °C with a 1:1 precursor-to-activator ratio (C_K₂CO₃_800) showed the highest CO₂ adsorption capacity of 6.26 mmol/g at 0 °C and 1 bar. Nitrogen adsorption–desorption analysis confirmed a predominantly microporous structure, with ultramicropores (0.3–0.7 nm) primarily responsible for the high CO₂ uptake. The Sips model provided the best fit to the adsorption equilibrium data, indicating a heterogeneous surface. The isosteric heat of adsorption (22–26 kJ/mol) confirmed a physical adsorption mechanism. Furthermore, the CO₂/N₂ selectivity, evaluated using the Ideal Adsorbed Solution Theory (IAST), reached values up to 18 at low pressures, highlighting the excellent separation performance. These findings demonstrate that avocado seed-derived activated carbons prepared with K₂CO₃ are efficient, renewable, and environmentally friendly sorbents for CO₂ capture, combining high adsorption capacity with sustainability and ease of synthesis. Full article

This study systematically investigates the pore–fracture architecture of deep coal seams in the JiaTan (JT) block of the Ordos Basin using an integrated suite of advanced techniques, including nuclear magnetic resonance (NMR), high-pressure mercury intrusion, low-temperature nitrogen adsorption, low-pressure carbon dioxide adsorption, and micro-computed tomography (micro-CT). These complementary methods enable a quantitative assessment of pore structures spanning nano- to microscale dimensions. The results reveal a pore system overwhelmingly dominated by micropores—accounting for more than 98% of the total pore volume—which play a central role in coalbed methane (CBM) storage. Microfractures, although limited in volumetric proportion, markedly enhance permeability by forming critical flow pathways. Together, these features establish a dual-porosity system that governs methane transport and recovery in deep coal reservoirs. The multiscale characterization employed here proves essential for resolving reservoir heterogeneity and designing effective stimulation strategies. Notably, enhancing methane desorption in micropore-rich matrices and improving fracture connectivity are identified as key levers for optimizing deep CBM extraction. These insights offer a valuable foundation for the development of deep coalbed methane (DCBM) resources in the Ordos Basin and similar geological settings. Full article

In this work, zeolitic imidazolate frameworks (ZIF-8, ZIF-67, and ZC-ZIF) and their hybrid composites with carboxylate-functionalized carbon nanotubes (fCNTs) are synthesized through low-cost synthesis methods for enhanced physisorption-based hydrogen storage at room temperature. While both base and hybrid structures are designed to improve hydrogen uptake, the base materials exhibit the most notable performance compared to their carbon hybrid counterparts. The structural analysis confirms that all samples maintain high crystallinity and exhibit well-defined rhombic dodecahedral morphologies. The hybrid composites, due to the intercalation of fCNTs, show slightly larger particle sizes than their base materials. X-ray photoelectron spectroscopy reveals strong nitrogen–metal coordination in the ZIF structures, contributing to a larger specific surface area (SSA) and optimal microporous properties. A linear fit of SSA and hydrogen uptake indicates improved hydrogen transport at low pressures due to fCNT addition. ZIF-8 achieves the highest SSA of 2023.6 m²/g and hydrogen uptake of 1.01 wt. % at 298 K and 100 bar, with 100% reversible adsorption. Additionally, ZIF-8 exhibits excellent cyclic repeatability, with only 10% capacity reduction after five adsorption/desorption cycles. Kinetic analysis reveals that hydrogen adsorption in the ZIF materials is governed by a combination of surface adsorption, intraparticle diffusion, and complex pore filling. These findings underscore the potential of ZIFs as superior materials for room-temperature hydrogen storage. Full article

Carbon dioxide (CO₂) storage in sandstones is vital for enhancing oil/gas recovery and reducing CO₂ emissions. The introduction of CO₂ into sandstone reservoirs leads to chemical reactions between CO₂ and minerals present in sandstone, which changes the pore structure of the sandstone reservoir. Herein, tight sandstone samples from the Coal-Measure Strata of the Shanxi Formation in the Huxiang area, Henan Province, were selected for simulation in this experimental study under supercritical CO₂ (ScCO₂)–H₂O treatment in reservoir conditions. Further, mercury intrusion porosimetry and low-pressure nitrogen adsorption/desorption methods were used to analyze the evolution of the pore structures of tight sandstones, and the mechanism of pore structure evolution was discussed. The results show that pore volumes and specific surface areas in the micropores and transitional pores decreased after the ScCO₂–H₂O treatment, while those in the mesopores and macropores increased. In the micropores and transitional pores, some of the pores changed from open pores and ink-bottle-shaped pores to semi-closed pores after the ScCO₂–H₂O treatment, and the pore morphology became narrower, which might have deteriorated the pore connectivity. A pore structure evolution model of ScCO₂–H₂O-treated tight sandstones was proposed. The evolution of pore structure is a result of the synergistic effect of pore enlargement caused by mineral dissolution and secondary mineral precipitation, which together play a controlling role in pore structure evolution. This study is conducive to understanding the pore structure evolution under ScCO₂–H₂O treatment and implementing CO₂ storage and enhancing oil/gas recovery in sandstone reservoirs. Full article

The massive emission of low-concentration coal mine methane (CMM) has resulted in the ineffective utilization of a large amount of energy methane and caused environmental pollution. The gas mixture used in the study consisted of methane (CH₄) 12% and nitrogen (N₂) 88%. The adsorbent was coconut activated carbon. This paper uses the adsorption method to conduct enrichment research on 12% low-concentration CMM. Firstly, the variation in methane gas concentration under different desorption methods was studied by numerical simulation, and the desorption methods suitable for increasing methane concentration were analyzed. A three-bed VPSA CMM separation experimental device was built, and three enrichment processes of feed gas pressurization, exhaust gas pressurization, and vacuum exhaust (VE) were studied. The results show that using the three-bed vacuum pressure swing adsorption (VPSA) process can effectively enrich low-concentration CMM. Under the adsorption pressure of 110 kPa and the desorption pressure of 10 kPa, 12% of CMM can be enriched to more than 25%, with a recovery rate higher than 80%. The exhaust process can significantly increase the product gas concentration. The product gas concentration increased by 18.2%, with the product rising from 22.5% to 26.6% when the extraction step increased from 0 s to 8 s. This research may provide reliable fundamental data for industrial-scale low-concentration CMM enrichment. Full article

Vibrations caused by downhole operations often induce coal and gas outburst accidents in tectonic zone coal seams. To clarify how vibration affects the pore structure, gas desorption, and diffusion capacity of tectonic coal, isothermal adsorption-desorption experiments under different vibration frequencies were carried out. In this study, high-pressure mercury intrusion experiments and low-pressure liquid nitrogen adsorption experiments were conducted to determine the pore structures of tectonic coal before and after vibration. The pore distribution of vibration-affected tectonic coal, including local concentration, heterogeneity, and connectivity, was analyzed using multifractal theory. Further, a correlation analysis was performed between the desorption diffusion characteristic parameters and the pore fractal characteristic parameters to derive the intrinsic relationship between the pore fractal evolution characteristics and the desorption diffusion characteristics. The results showed that the vibration increased the pore volume of the tectonic coal, and the pore volume increased as the vibration frequency increased in the 50 Hz range. The pore structure of the vibration-affected tectonic coal showed multifractal characteristics, and the multifractal parameters affected the gas desorption and diffusion capacity by reflecting the density, uniformity, and connectivity of the pore distribution in the coal. The increases in the desorption amount (Q), initial desorption velocity (V₀), initial diffusion coefficient (D₀), and initial effective diffusion coefficient (D_e) of the tectonic coal due to vibration indicated that the gas desorption and diffusion capacity of the tectonic coal were improved at the initial desorption stage. Q, V₀, D₀, and D_e had significant positive correlations with pore volume and the Hurst index, and V0, D0, and De had negative correlations with the Hausdorff dimension. To a certain extent, vibration reduced the local density regarding the pore distribution in the coal. As a result, the pore size distribution was more uniform, and the pore connectivity was improved, thereby enhancing the gas desorption and diffusion capacity of the coal. Full article

Zeolitic imidazolate frameworks (ZIFs) are traditionally synthesized using N, N-dimethylformamide (DMF). However, DMF is toxic and hazardous to human health and the environment, hence other alternative solvents need to be considered. Herein, three different solvents like methanol, water and acetone were used to replace DMF and to explore the syntheses of ZIF-90 using a conventional and a microwave-assisted solvothermal method to obtain hydrothermally stable products, which also exhibit an increased water uptake. Pure ZIF-90 was synthesized under ambient pressure at 60 °C for 90 min using the conventional solvothermal method in an acetone–water solution, while under microwave irradiation it was formed in only 5 min at 80 °C. Altering methanol, water and acetone in the reaction mixture significantly affected the structural and water adsorption properties of ZIF-90s, which were monitored via PXRD, TGA, nitrogen and water sorption, and SEM. The highly efficient, less toxic, low-cost and activation-free microwave synthesis resulted in the formation of ZIF-90 nanoparticles that exhibited the highest maximum water adsorption capacity (0.37 g/g) and the best hydrothermal stability between water adsorption at 30 °C and desorption at 100 °C at 12.5 mbar among all the products obtained. Full article

An efficient catalyst is key to achieving the synthesis of electrochemical ammonia and improving safety. In this work, using biomass walnut shell as a carbon source and sodium thiosulfate as a sulfur source, sulfur-modified walnut shell-derived carbon material was synthesized via a simple low-temperature impregnation method at room temperature and atmospheric pressure as an effective electrochemical ammonia synthesis catalyst with high thermal stability. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption apparatus, thermogravimetry (TG), and other characterization methods were applied to analyze the micro-morphology and physicochemical structure of the electrocatalyst. The synthesized ammonia performance of the catalyst was measured using an ultraviolet (UV) spectrophotometer and electrochemical workstation. The catalyst design used the doping of sulfur atoms to create rich catalytic active sites, while the presence of elemental sulfur on the catalyst surface provided hydrophobicity, which was conducive to inhibiting competitive hydrogen evolution reaction (HER) and enhancing the electrocatalytic ammonia synthesis performance of the catalyst. Under normal temperature and pressure conditions, when a voltage of −0.45 V was applied, the ammonia yield in 0.05 M H₂SO₄ electrolyte was 10.39 μg_NH3 mg_cat.⁻¹ h⁻¹. The results showed that the introduction of sulfur effectively improved the electrocatalytic and thermal safety performance of bio-derived carbon materials, and the test presented that the performance of the catalyst was stable and reusable. Full article

Shale in the Jurassic Lianggaoshan Formation in central Sichuan exhibits strong heterogeneity. The study of the pore structure characteristics of different lithologies is crucial to the selection of the target interval. Shale samples of the Lianggaoshan Formation from well YS5 in the central part of the Sichuan Basin were analyzed using scanning electron microscopy, low-temperature nitrogen adsorption, high-pressure mercury injection (HPMI), and large -field splicing method -based scanning electron microscopy (LFS-SEM) to elucidate the pore structure characteristics of shale and their influencing factors. The mineral composition of the reservoir in the study area was diverse, primarily consisting of clay minerals, followed by quartz and calcite. The reservoir space comprised intergranular, granular, and organic matter pores, and oil was observed to fill the reservoir space. Reservoir characteristics varied with the lithological properties. In clayey shale, intergranular pores located in clay mineral particles and pores between pyrite and natural fractures were mainly observed, with a bimodal distribution of pore size and peak distribution of 10–50 nm and >100 nm. The storage space of ash-bearing shale mainly consisted of intragranular pores and intergranular (crystalline) micropores, with pore sizes primarily concentrated in the 10–50 nm range. The storage space in silty shale mainly developed in clastic mineral particles such as quartz, followed by clay mineral intergranular pores with a relatively wide distribution of sizes. Pores were mainly inkbottle-shaped and slit-type/plate-type pores, with an average specific surface area of approximately 6.9046 m²·g⁻¹ and an average pore volume of approximately 0.0150 cm³·g⁻¹. The full-pore capillary pressure curve was established using a combination of gas adsorption–desorption tests and HPMI. The fractal dimension of the sample pore structure was calculated, and a significant linear correlation was found between clay mineral content and the fractal dimension. Thus, the pore structure characteristics were mainly controlled by the content and distribution of clay minerals. Full article

Exploring the compressibility of the deeply buried marine shale matrix and its controlling factors can help achieve efficient petroleum production. Taking ten sets of deeply buried marine shale core samples from Ning228 wells in the Yanjin area as an example, the matrix compressibility and pore characteristics of deeply buried marine shale reservoirs were investigated by applying mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption isotherms at a low temperature of 77 K. Mathematical models (based on MIP and nitrogen adsorption/desorption isotherms) were established to analyze the effects of TOC, mineral components, and pore structure on matrix compressibility. The relationship between the compressibility coefficient and the brittleness index was also established. The results show that the compressibility of the shale matrix is significant when the mercury injection pressure ranges from 8.66 to 37 MPa. For deeply buried marine shale, the matrix compressibility is in the range of 0.23 × 10⁻⁴–22.03 × 10⁻⁴ MPa⁻¹. The influence of TOC and minerals on matrix compressibility is mainly reflected in the control effect of pore structure. High TOC content decreases the overall shale elastic modulus, and high clay mineral content enhances shale stress sensitivity, resulting in a significant matrix compressibility effect. For the effect of pore structure on compressibility, the pore content in shale has a positive effect on matrix compressibility. In addition, the pore-specific surface area is critical to the effective variation of shale matrix compressibility, indicating that the complexity of the shale pore structure is a key factor affecting matrix compressibility. Full article

Gas prevention and control have always been the focus of coal mine safety. The pore structure characteristics and gas adsorption characteristics of coal seams are the key factors affecting gas adsorption and diffusion in coal seams. Lvjiatuo Mine has the characteristics of a high gas content when it enters deep mining. In order to clarify the influence of the pore-fracture structure characteristics of main coal seams in the research area on coal seam gas adsorption and diffusion, and to study the differences in gas adsorption and diffusion ability in different coal seams, low-temperature nitrogen adsorption (LT-N₂GA), high-pressure mercury intrusion (MIP) and computerized tomography (μ-CT) were used as characterization methods, and methane isothermal adsorption experiments were carried out to systematically study the pore structure characteristics of five groups of coal samples, and the pore-fracture structure characteristics and gas adsorption characteristics of each main coal seam were obtained. The results show that: (1) in the LT-N₂GA experiment, the adsorption–desorption curves of all coal samples are of type III, and mainly develop cone-shaped pores or wedge-shaped semi-closed pores, with an average pore size of 1.84~4.84 nm, a total pore volume of 0.0010~0.0023 mL/g, a total specific surface area of 0.16~0.24 m²/g, and a fractal dimension D₁ of 1.39~1.87 and D₂ of 2.44~2.60. The micropores of L12 are more developed, and the mesopores and macropores of L9 are more developed. (2) In the MIP experiment, the porosity of coal samples is 3.79~6.94%. The porosity of L9 is the highest, the macropore ratio is the highest, and the gas diffusion ability is also the strongest. (3) In the μ-CT experiment, the porosity of L8-2 and L12 is 12.12% and 10.41%, the connectivity is 51.22% and 61.59%, and the D_f is 2.39 and 2.30, respectively. The fracture of L12 is more developed, the connectivity is better, and the heterogeneity of the pore of L8-2 is higher. (4) In the isothermal adsorption experiment of methane, the gas adsorption capacity basically increases with the increase in the buried depth of the coal seam, and the gas adsorption capacity of the No.12 coal seam is the highest. Based on the pore-fracture structure characteristics and gas adsorption characteristics of the main coal seams in the research area, the gas outburst risk of each coal seam is ranked as follows: No.12 coal seam > No.8 coal seam > No.7 coal seam > No.9 coal seam. The experimental results provide important help for researching the structural characteristics of coal seam pore fractures and preventing gas outbursts during deep coal seam mining. Full article

The oxidative dehydrogenation of alkanes is a prospective method for olefins production. CO₂-assisted propane dehydrogenation over metal oxide catalysts provides an opportunity to increase propylene production with collateral CO₂ utilization. We prepared the chromia catalysts on various mesoporous aluminosilicate supports, such as halloysite nanotubes, nanostructured core/shell composites of MCM-41/halloysite (halloysite nanotubes for the core; silica of MCM-41-type for the shell), and MCM-41@halloysite (silica of MCM-41-type for the core; halloysite nanotubes for the shell). The catalysts have been characterized by X-ray fluorescence analysis, low-temperature nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption of ammonia, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. The catalysts’ performance in carbon-dioxide-assisted propane dehydrogenation has been estimated in a fixed-bed reactor at atmospheric pressure. The most stable catalyst is Cr/halloysite, having the lowest activity and the largest pore diameter. The catalyst, Cr/MCM-41/HNT, shows the best catalytic performance: having the highest conversion (19–88%), selectivity (83–30%), and space–time yield (4.3–7.1 mol C₃H₆/kg catalyst/h) at the temperature range of 550–700 °C. The highest space–time yield could be related to the uniform distribution of the chromia particles over the large surface area and narrow pore size distribution of 2–4 nm provided by the MCM-41-type silica and transport channels of 12–15 nm from the halloysite nanotubes. Full article

A new phosphorous-free rhodium supported on a nitrogen-doped silica was successfully used as a catalyst for the hydroformylation of alkenes. The obtained material and the catalyst were characterized by XRD, XPS, FTIR, SEM, TEM, ICP AES, and low-temperature nitrogen adsorption–desorption measurements. The catalytic performance was studied by the example of the hydroformylation of octene-1 at temperatures of 80–140 °C and a pressure of 5.0 MPa. The catalyst provided a 99% conversion of 1-octene with a 98% yield of aldehydes and showed a good conversion of styrene and cyclohexene. The catalyst can be repeatedly used in ten consecutive cycles, with its activity remaining constant. Full article

Hydrogen adsorption measurements were taken by the weighting method using the Sartorius low-pressure microbalance. Experiments were conducted at two temperatures: 77.5 and 300 K; the adsorbent used was active carbon obtained from wood and modified with potassium hydroxide. The porous structure of the carbon prior to and after modification was evaluated based on the nitrogen adsorption and desorption data. Thus, the densimetric characteristic of active carbon was modified; porous structures were developed in the range of micro-, meso- and macropores and the volume of hydrogen adsorbed at 77.5 K showed an almost four-fold increase. Modified active carbons are found to be suitable for applications in hydrogen storage systems. Full article