Carbon monoxide, dinitrogen and carbon dioxide adsorption on zeolite H-Beta: IR spectroscopic and thermodynamic studies

Variable temperature IR spectroscopy (VTIR) was used to investigate the adsorption thermodynamics of carbon monoxide, dinitrogen and carbon dioxide on the protonic zeolite H-Beta. Interaction of the adsorbed gases with the zeolite Brønsted acid sites was found to involve an enthalpy change of −27, −19 and −33 kJ mol⁻¹ for CO, N₂ and CO₂, respectively; the corresponding entropy change was −150, −140 and −146 J mol⁻¹ K⁻¹. The adsorbed gases showed also a weak interaction with silanols, which involves a ΔH⁰ value in the approximate range of −7 to −10 kJ mol⁻¹. These results were discussed in the context of gas separation and carbon capture and sequestration (CCS) using zeolites.     

Effect of mesoporous silica modification on the structure of hybrid carbon membrane for hydrogen separation

An SBA-15/carbon molecular sieve (CMS) composite membrane, using polyetherimide as a precursor and mesoporous silica as filler, was fabricated for hydrogen separation. The effect of mesoporous SBA-15 on the gas transport properties of the composite membrane was evaluated. The permeability and selectivity coefficients of H₂, CO₂, O₂, N₂, and CH₄ were estimated for the pure CMS and SBA-15/CMS composite membranes at a feed pressure of 2-7 atm for 30 °C. The SBA-15/CMS composite membrane had a gas permeability higher than that of the pure CMS membrane, whereas its selectivity was the same. The permeability was found to be independent of pressure; this indicates that the gases are transported through the membrane by a molecular sieve mechanism. The membranes appeared to have a more microporous structure when the mesoporous silica SBA-15 was incorporated. These results concur with the hypothesis that SBA-15 improves gas diffusivity by increasing pore volume.     

Facile synthesis of nitrogen-enriched mesoporous carbon for carbon dioxide capture

To investigate carbon dioxide adsorption behaviors, we prepared mesoporous carbon (MC) materials that incorporated framework nitrogen functional groups via a facile polymerization-induced colloid aggregation (PICA) procedure, where the nitrogen content varied as a function of carbonization temperature. The prepared MCs had high specific surface areas (e.g., 974 m²/g) with well-developed mesopores. The highest carbon dioxide adsorption capacity of 106 mg/g at 25 °C was achieved with the MCs-800 sample (carbonization temperature of 800 °C). We found that the materials prepared in this study were highly effective for carbon dioxide capture, because the nitrogenous functional groups in the MCs enhanced their affinities for acidic carbon dioxide.     

Carbon dioxide reforming of methane to syngas over ordered mesoporous Ni/KIT-6 catalysts

The ordered mesoporous Ni/KIT-6 (KIT-6, an ordered mesoporous SiO₂) catalysts were prepared by impregnation method for carbon dioxide reforming of methane. The physicochemical properties of the prepared catalysts were characterized by H₂-TPR, XRD, BET, and TEM. The research results show that the specific surface area, pore diameter, crystal size of Ni species, and catalytic performance of the Ni/KIT-6 catalysts are obviously affected by the Ni content. Increasing Ni content results in the increment of the crystal size of Ni species, while the dispersion of Ni species shows the opposite trend. The specific surface area and pore size of the Ni/KIT-6 catalyst with the Ni loading of 3 wt% were 493.3 m² g^?1 and 6.22 nm, respectively. Besides, the Ni species are highly dispersed on the surface of KIT-6 support. Thereby, it exhibits the superior catalytic performance of carbon dioxide reforming of methane to syngas (CO and H₂). At atmospheric pressure, the CO₂ and CH₄ conversions for each catalyst following the order: NK3 ≈ NK4 > NK5 > NK2 > NK1 > bulk Ni. When the reaction temperature is 600 °C, the conversions of CH₄ and CO₂ of the NK3 catalyst are 65.1% and 37.0%, respectively. Meanwhile, it also shows excellent stability.     

Carbon dioxide vent for direct methanol fuel cells

Passive, stand-alone, direct methanol fuel cells require a pressure management system that releases CO₂ produced in the anode chamber. However, this must be done without allowing the methanol fuel to escape. In this paper, two siloxane membranes are investigated and shown to selectively vent CO₂ from the anode chamber. The addition of hydrophobic additives, 1,6-divinylperfluorohexane and 1,9-decadiene, improved the selectivity of the siloxane membranes. The best performing CO₂ vent was obtained with 50:50 wt% poly(1-trimethyl silyl propyne) and 1,6-divinylperfluorohexane.     

Composite sorbent of methanol “LiCl in mesoporous silica gel” for adsorption cooling: Dynamic optimization

A novel composite sorbent of methanol “LiCl in mesoporous silica gel” has recently been proposed for AC (adsorption cooling). Its testing in a lab-scale adsorption chiller resulted in the specific cooling power of 210-290 W/kg and the cooling COP of 0.32-0.4. Although these values are rather encouraging, a room for their enhancement still exists. The aim of this paper was a dynamic optimization of the composite performance in AC cycles. Dynamics of methanol sorption on loose grains of the LiCl/silica composites was studied by a Large Temperature Jump method under typical conditions of AC cycle. Effects of number of the sorbent layers, salt content, grain size and cycle boundary temperatures were studied. Physico-chemical processes in the three-phase system (salt, solution, vapor) were shown to be quite complex and can strongly affect the dynamics of methanol ad-/desorption. Several obstacles which can retard the sorption were analyzed. Appropriate recommendations on improving the cycle dynamics, which concern optimal conversion degree, salt content and relative durations of ad- and desorption phases, were made.     

Ordered mesoporous alumina supported nickel based catalysts for carbon dioxide reforming of methane

Ordered mesoporous alumina facilely synthesized via improved evaporation-induced self-assembly (EISA) strategy was provided with large specific surface area, big pore volume, uniform pore size and excellent thermal stability. The obtained mesoporous material was used as the carrier of the Ni based catalysts for carbon dioxide reforming of methane. These mesoporous catalysts performed high catalytic activity and long stability. Typically, the catalytic conversions of the CH₄ and CO₂ were greatly close to the equilibrium conversion and no deactivation was observed during the 100 h long lifetime test. The advantageous structural properties of ordered mesoporous alumina contributed to high dispersion of the Ni particles among the mesoporous framework, which further accounted for the good catalytic activity due to more “accessible” Ni active sites for the reactants. The “confinement effect” of the mesopores could effectively prevent the thermal sintering of the Ni nanoparticles to some extent, committed to its long-term catalytic stability. Besides, the mesoporous catalysts possessed enhanced ability to withstand coke, although not any modifiers had been added. Properties of the coke over the mesoporous catalyst were also carefully investigated. Therefore, the ordered mesoporous alumina was a promising catalyst support for the carbon dioxide reforming with methane.     

Methanation of carbon dioxide over Ni/CeO2 catalysts: Effects of support CeO2 structure

The CeO₂, which were prepared by hard-template method, soft-template method, and precipitation method, were used as support to prepare Ni/CeO₂ catalysts (named as NCT, NCS, and NCP catalysts, respectively). The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET). Hydrogen temperature-programmed reduction (H₂-TPR) was also used to study the reducibility of the support nickel precursors. Moreover, CO₂ catalytic hydrogenation methanation was used to investigate the catalytic properties of the prepared NCT, NCS, and NCP catalysts. H₂-TPR and XRD results showed that the NiO can be reduced by H₂ to produce metal Ni species, and the surface oxygen species existing on the surface of the support CeO₂ can also be reduced by H₂ to form surface oxygen vacancies. Low-angle XRD, TEM, and BET results indicated that the NCT and NCS catalysts had developed mesoporous structure and high specific surface area of 104.7 m² g^?1 and 53.6 m² g^?1, respectively. The NCT catalyst had the highest CO₂ methanation activity among the studied NCT, NCS, and NCP catalysts. The CO₂ conversion and CH₄ selectivity of the NCT catalyst can reach 91.1% and 100% at 360 °C and atmospheric pressure. The NCP catalyst, which had low specific surface area and low porosity, performed less CO₂ conversion and higher CH₄ selectivity than the NCT and NCS catalysts till 400 °C.     

Computational analysis of atomic C and S adsorption on Ni,Cu, and Ni-Cu SOFC anode surfaces

Carbon deposition and sulfur poisoning are issues that limit the state-of-the-art Ni-YSZ anode material of solid oxide fuel cell to be used in direct hydro-carbon fuels. In the present study, density functional theory calculations are performed to investigate the adsorption of C and S on Ni(111), Cu(111) and alloyed Ni-Cu(111) surfaces. It is confirmed that C and S energetically favor the hollow sites of Ni(111) and Cu(111) surfaces; forming Ni-Cu alloy by addition of Cu into Ni weakens the adsorption of C and S with lowered adsorption energies due to less overlapping between the C 2p or S 3p and the metallic 3d orbits.     

In-situ decoration of Pd nanocrystals on crystalline mesoporous NiO nanosheets for effective hydrogen gas sensors

The synthesis of cost-effective, high-performance hydrogen gas sensors is eliciting increasing interest because of their advantages in early detection of hydrogen leakages. Herein, we report the in-situ synthesis and decoration of Pd nanocrystals (NCs) on the surface of mesoporous NiO nanosheets for effective hydrogen gas sensor application. The use of large specific surface area of the mesoporous NiO nanosheets and the catalytic activity of the Pd NCs are the key points to improve the hydrogen gas-sensing performances through the enhancement of the interaction between the hydrogen molecule and the sensing surface. The mesoporous NiO nanosheets were fabricated by a surfactant-less hydrothermal method in sequence to thermal oxidation, whereas the Pd NCs were decorated by in-situ reduction of palladium complex. The crystal structure and growth mechanism of the materials were investigated by several advanced techniques. The gas-sensing measurements revealed that the Pd-NiO nanosheets based sensor exhibited effectively detection of hydrogen at low concentration with fast response, high sensitivity and stability.     

Static and dynamic studies of hydrogen adsorption on nanoporous carbon gels

Although hydrogen is considered to be one of the most promising green fuels, its efficient and safe storage and use still raise several technological challenges. Physisorption in porous materials may offer an attractive means of $H_2$ storage, but the state-of-the-art capacity of these kinds of systems is still limited. To overcome the present drawbacks a deeper understanding of the adsorption and surface diffusion mechanism is required along with new types of adsorbents developed and/or optimised for this purpose. In the present study we compare the hydrogen adsorption behaviour of three carbon gels exhibiting different porosity and/or surface chemistry. In addition to standard adsorption characterisation techniques, neutron spin-echo spectroscopy (NSE) has been also applied to explore the surface mobility of the adsorbed hydrogen. Our results reveal that both the porosity and surface chemistry of the adsorbent play a significant role in the adsorption of $H_2$ in these systems.     

Ni and Ni3C catalysts supported on mesoporous silica for dry reforming of methane

Ni and Ni₃C catalysts supported on nano-sized and mesoporous silica were used to study the dry reforming reaction of biogas. Ni catalysts were deposited over either nano-sized silica or a novel mesoporous silica (450 m²/g), which were the main supports used in this study. Subsequently, a secondary active phase (Pt) and support (MgO) were added. In addition, mesoporous-supported Ni was also subjected to a carburization process with CH₄. Size effects, preparation techniques and chemical nature of co-supports were studied. Catalytical, microstructural, chemical and molecular characterization of fresh and spent materials were carried out using BET, H₂-TPR, XRD, HRTEM, WDXRF, and Raman spectroscopy. The reaction was undertaken at 700 °C and 1 atm. Results evidence that catalyst supported on both mesoporous silica and also nickel carbide catalyst presented high stability and slow deactivation overall in spite the high content of carbon. The addition of Pt did not increase stability of the catalysts.     

A review on adsorption cooling systems with adsorbent carbon

This study introduces a review for the potential cooling systems which uses carbon materials as an adsorbent. Also, the adsorption carbon pairs (pairs where the carbon is the adsorbent) which is still under researches were reviewed. The maximum COP (coefficient of performance) of the cooling systems was 0.8 for activated carbon/ethanol pair. The study concluded that the performances of the potential adsorption cooling systems using carbon are still not satisfied. It was concluded that there is an opportunity for the adsorption carbon pairs to introduce a new cooling system with a promising performances.     

征收碳税对我国二氧化碳减排的影响

我国的大气污染问题亟需大力整治,调整以煤为主的能源结构是根本途径,体现环境成本与征收碳税是重要方法之一,且在国外已有成功经验.本文利用联立方程模型,通过假设不同碳税征收的情景,分析碳税对我国原油、天然气及煤炭消费的影响,继而测算对二氧化碳减排的影响.结果表明,征收碳税可对碳减排起到显著的作用,可促使能源结构向清洁化发展,化石能源消费受到抑制,但受影响程度不同,煤炭消费受影响最大,天然气消费受影响最小.在碳税征收上应采取循序渐进的征收方式,避免对经济和行业发展产生较大冲击.     

CO2 separation from the mixture of CO2/H2 using gas hydrates: Experimental and modeling

Hydrate formation is a new technique to separate hydrogen from carbon dioxide. In this way, modeling and prediction of gas hydrate kinetics is very important. Several experiments have been conducted to study the hydrate formation from pure carbon dioxide and mixture of hydrogen and carbon dioxide in a stirred reactor in different temperatures, pressures and compositions. The mass transfer approach model was used to predict the mass transfer coefficient for each experiment, and the dependency of temperature and pressure has been studied. It was observed that the mass transfer coefficient of CO₂ in the mixture is close to the pure system. The result of this work shows that the pure data on the kinetics for CO₂ hydrate formation is applicable for the case of CO₂ separation from the mixture of carbon dioxide and hydrogen.     

Carbon dioxide reforming of methane over nickel catalysts supported on TiO2(001) nanosheets

As we all know, the critical problem of nickel catalysts for carbon dioxide reforming of methane is the deactivation of catalysts due to the carbon deposition and sintering of the active components under high temperature. It was reported that anatase TiO₂ nanosheets with high-energy (001) facets had strong interaction with nickel, which was probably beneficial to resist sintering of nickel nanoparticles and to eliminate deposited carbon via oxygen migration. In this study, Ni nanoparticles were supported on TiO2 nanosheets with exposed high-energy (001) facets. The Ni/TiO₂(001) catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, physisorption of N₂, X-ray photoelectron spectroscopy and H₂ temperature-programmed reduction, and the spent catalysts were characterized by Roman and thermogravimetry analysis. The catalytic performance of Ni/TiO₂(001) catalysts were measured for carbon dioxide reforming of methane reaction. It was found that the prepared Ni/TiO₂(001) catalysts showed reasonably higher catalytic activity and stability compared with the nickel catalyst supported on commercial titanium oxide (P25). The high dispersion of nickel nanoparticles of Ni/TiO₂(001) catalysts was helpful to the resistance towards carbon deposition and the strong metal-support interaction was helpful to the resistance towards nickel sintering on account of the unusual surface properties of TiO₂(001).     

Analysis of adsorption equilibrium of hydrogen on graphene sheets

The adsorption equilibrium of hydrogen on graphene sheets (GS) was studied based on a sample of GS with S_BET = 300 m²/g at the temperatures of 77.15 K–293.15 K and the pressures of 0 MPa–6 MPa. In the meantime, the adsorptions (Excess adsorption measurements) of hydrogen on granular coconut shell SAC-02 activated carbon (S_BET = 2074 m²/g) and carbon nanofiber (CNFs, S_BET = 205 m²/g) were investigated at the pressures of 0–8 MPa and the temperature of 77.15 K. The outcomes from experiments were used to determine the parameters in Toth equation by way of Non-linear fit. The absolute adsorption amounts of hydrogen on the GS, which were calculated from the equation, were used to calculate the isosteric heat of hydrogen adsorption by use of adsorption isosteres.     

Hydrogen purification using compact pressure swing adsorption system for fuel cell

Adsorption of CO and CO₂ in mixtures of H₂/CO/CO₂ was achieved using compact pressure swing adsorption (CPSA) system to produce purified hydrogen for use in fuel cell. A CPSA system was designed by combining four adsorption beds that simultaneously operate at different processes in the pressure swing adsorption (PSA) process cycle. The overall diameter of the cylindrical shell of the CPSA is 35 cm and its height is 40 cm. Several suitable adsorbent materials for CO and CO₂ adsorption in a hydrogen stream were identified and their adsorption properties were tested. Activated carbon from Sigma–Aldrich was the adsorbent chosen. It has a surface area of 695.07 m²/g. CO adsorption capacity (STP) of 0.55 mmol/g and CO₂ at 2.05 mmol/g were obtained. The CPSA system has a rapid process cycle that can supply hydrogen continuously without disruption by the regeneration process of the adsorbent. The process cycle in each column of the CPSA consists of pressurization, adsorption, blowdown and purging processes. CPSA is capable of reducing the CO concentration in a H₂/CO/CO₂ mixture from 4000 ppm to 1.4 ppm and the CO₂ concentration from 5% to 7.0 ppm CO₂ in 60 cycles and 3600 s. Based on the mixture used in the experimental work, the H₂ purity obtained was 99.999%, product throughput of 0.04 kg H₂/kg adsorbent with purge/feed ratio was 0.001 and vent loss/feed ratio was 0.02. It is therefore concluded that the CPSA system met the required specifications of hydrogen purity for fuel cell applications.     

Human population and carbon dioxide

A recently proposed model of human population and carbon utilization is reviewed. Depending on parameter values, one of three possible long-term outcomes is obtained. (1) Atmospheric carbon, (CO₂)_atm, and human populations equilibrate at positive values. (2) The human population stabilizes, while (CO₂)_atm increases without bound. (3) The human population goes extinct and atmospheric carbon declines to 0. The final possibility is qualitatively compatible with both “consensus” views of climate change and the opinions of those who are more impressed with the manifestly adverse consequences of carbon-mitigation to human reproduction and survival.