Amino-modified molecular sieves for adsorptive removal of H2S from natural gas

Amine-modified MCM-41 adsorbents (APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41) were prepared and characterized by XRD, N₂ adsorption–desorption, FT-IR, TEM, SEM and TG-DTA. The performance of each adsorbent in a fixed adsorption bed for H₂S removal was measured using a mixture of oxygen, nitrogen and hydrogen sulfide gases. It was found that the specific surface area decreased and the topography changed significantly after the use of each modified adsorbent. Nevertheless, all amine-modified MCM-41 adsorbents retained mesoporous silica of MCM-41. The H₂S removal rate and saturated H₂S capacity of APTMS/MCM-41 improved from 32.3% to 54.2% and 119.5 to 134.4 mg g⁻¹, respectively, compared with that of MCM-41, and it showed the best performance among all adsorbents. APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41 were regenerated by maintaining at 423, 523 and 373 K in nitrogen for 3 h, respectively, and thus possessed high regenerability.

Several amine-modified MCM-41 adsorbents (APTMS/MCM-41, PEI/MCM-41, AAPTS/MCM-41) by the grafting method were prepared, in which APTMS/MCM-41 showed much better adsorptive desulfurization performance and regenerability than the others.     

Ultrasonic-assisted preparation of highly active Co3O4/MCM-41 adsorbent and its desulfurization performance for low H2S concentration gas

Co₃O₄/MCM-41 adsorbents were successfully prepared by ultrasonic assisted impregnation (UAI) and traditional mechanical stirring impregnation (TMI) technologies and characterized by X-ray diffraction (XRD), N₂ adsorption desorption, Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry-differential thermal analysis (TG-DTA). The H₂S removal performances for a simulated low H₂S concentration gas were investigated in a fixed-bed. The effect of preparation and adsorption conditions on the H₂S removal over Co₃O₄/MCM-41 were systematically examined. The results showed that UAI promotes more and well defined highly dispersed active Co₃O₄ phase on MCM-41. As compared to the Co₃O₄/MCM-41-T prepared via TMI, the saturated H₂S capacity of Co₃O₄/MCM-41-U prepared via UAI improved by 33.2%. The desulfurization performance of adsorbents decreased in the order of Co₃O₄/MCM-41-U > Co₃O₄/MCM-41-T > MCM-41. The Co₃O₄/MCM-41-U prepared using Co(NO₃)₂ concentration of 10%, ultrasonic time of 2 h, calcination temperature of 550 °C and calcination time of 3 h exhibited the best H₂S removal efficiency. At adsorption temperature of 25 °C with model gas flowrate of 20 mL min⁻¹, the breakthrough time of Co₃O₄/MCM-41-U was 10 min, and the saturated H₂S capacity and H₂S removal rate was 52.6 mg g⁻¹ and 47.8%, respectively.

Co₃O₄/MCM-41 adsorbent with high surface area and more active sites was successfully prepared by ultrasonic assisted impregnation (UAI) technology and it has been found that the sulfur capacity was improved by 33.2% because of ultrasonication.     

Preparation of recyclable MoO3 nanosheets for visible-light driven photocatalytic reduction of Cr(vi)

The exploitation of stable and earth-abundant photocatalysts with high catalytic activity remains a significant challenge for removing heavy metals from wastewater. Different from complex nanostructuring, this work focuses on a simple and feasible way to design catalysts. Herein, MoO₃ nanosheets were fabricated and grown vertically on the surface of a quartz tablet using a one-step chemical vapor deposition method. The morphology, construction and optical properties of the MoO₃ were characterized by XRD, XPS, SEM, HRTEM and UV-Vis methods, and the possible growth mechanism was also discussed. It can be found that the MoO₃ nanosheets exhibited significantly enhanced visible light photocatalytic reduction capacity with stable recyclability to Cr(vi). The results show that the MoO₃ nanosheets can be used as a cost-effective and recyclable photocatalyst for the removal of Cr(vi) from water. Our findings provide new inspiration for the design of new types of catalysts.

The exploitation of stable and earth-abundant photocatalysts with high catalytic activity remains a significant challenge for removing heavy metals from wastewater.     

Hydroxylation of benzene to phenol over heteropoly acid H5PMo10V2O40 supported on amine-functionalized MCM-41

Supported catalysts with Keggin type heteropoly acids (H₅PMo₁₀V₂O₄₀) loaded onto amine-functionalized MCM-41 for the catalytic hydroxylation of benzene to phenol with H₂O₂ were prepared by a wet impregnation method. The effects of the preparation conditions on the properties and activity of the supported catalysts were fully investigated. The results showed that the catalyst retained the mesoporous structure of MCM-41 and H₅PMo₁₀V₂O₄₀ was dispersed uniformly on the surface of the amine-functionalized MCM-41. Meanwhile, the reusability and catalytic performance of the catalyst were affected by two key factors, i.e., the interaction between the heteropoly acid and the surface of MCM-41, and the hydrophobicity of the catalyst since they decide the leaching of H₅PMo₁₀V₂O₄₀ and the adsorption of benzene. The catalyst with H₅PMo₁₀V₂O₄₀ loaded onto amine-functionalized MCM-41, which was prepared using ethanol as the solvent, exhibited the highest phenol yield (20.4%), a turnover frequency value of 20.3 h⁻¹ and good reusability. We believe this work offers an effective and facile strategy for the preparation of a new catalyst for hydroxylation of benzene to phenol.

Supported catalysts with heteropoly acid loaded onto amine-functionalized MCM-41 for hydroxylation of benzene to phenol are prepared.     

Visible-light-promoted and chlorophyll-catalyzed aerobic desulfurization of thioamides to amides

A novel method for the metal-free synthesis of amides from thioamides based on visible-light photoredox catalysis and in an air atmosphere is reported. Natural pigment chlorophyll is used as a photosensitizer to generate singlet molecular oxygen ¹O₂, which is involved in the aerobic desulfurization of thioamides. The protocol provides amides in good yields at room temperature under mild conditions. On the basis of experimental results, a plausible photoredox mechanism is proposed.

A visible-light-promoted desulfurization of thioamides to amides is reported. Natural pigment chlorophyll is used as a photosensitizer to generate singlet molecular oxygen ¹O₂ as oxidants.     

Bifunctional acid–base mesoporous silica@aqueous miscible organic-layered double hydroxides

A facile method for the synthesis of a series of mesoporous silica nanoporous (MSN) aqueous miscible organic layered double hydroxide core@shell nanocomposites using MCM-41, Al-MCM-41, SBA-15, and MCM-48 as the core is reported. These materials exhibit hierarchical morphologies with high surface areas and good porosity. Chemically, these materials offer controllable bifunctional basicity and acidity.

Core@shell materials which exhibit hierarchical morphology with ultra high surface area and controllable pore size and structure have been synthesised.     

Deep oxidative desulfurization of model fuels catalysed by immobilized ionic liquid on MIL-100(Fe)

Deep desulfurization of fossil fuels has become urgently required because of the serious pollution by the large-scale use of fossil fuels. In this study, [PrSO₃HMIm]HSO₄@MIL-100(Fe) was synthesized by wet-impregnation of the ionic liquid (IL) of [PrSO₃HMIm]HSO₄ on MIL-100(Fe). The construction of [PrSO₃HMIm]HSO₄@MIL-100(Fe) was then confirmed by X-ray powder diffraction, N₂ adsorption–desorption experiments, infrared spectroscopy and elemental analysis, and then applied in the oxidative desulfurization of model fuels. In comparison with the corresponding IL, [PrSO₃HMIm]HSO₄@MIL-100(Fe) showed an enhanced performance in the desulfurization rate of model fuels due to the increase of the mass transfer rate. Under the optimized conditions (oxidant to sulphur ratio = 25, oil to acetonitrile ratio = 1, and temperature = 60 °C), a sulphur removal rate of 99.3% was observed (initial sulphur concentration = 50 ppm). The sulphur removal of three sulphur compounds by catalytic oxidation and extraction followed the order of dibenzothiophene (DBT) > thiophene (T) > benzothiophene (BT).

ILs@MIL-100 composites were synthesized via the wet impregnation method and applied in deep oxidative desulfurization of gasoline with high efficiency.     

Effect of cobalt addition on the structure and properties of Ni–MCM-41 for the partial oxidation of methane to syngas

A one-step hydrothermal crystallization method was used to synthesize Co–Ni–MCM-41 catalysts for the partial oxidation of methane to syngas reaction. Co was added as an assistant in the synthesis process. The formation of a Ni–Co alloy decreased the damage of Ni ions to the framework of MCM-41. The Ni–Co alloy introduced more Ni into the channel exposing more active sites. The properties of the synthesized catalysts were characterized by XRD, N₂ adsorption–desorption, TEM, ICP, FT-IR, H₂-TPR, XPS and TGA techniques. Co–Ni–MCM-41 catalysts showed superior catalytic performance and sintering resistance than Ni–MCM-41 catalyst without Co. The Ni–Co alloy inhibited the formation of the NiO, thus reducing the sintering of the catalyst. The result was attributed to higher metal dispersion and more regular pore structure of the Co–Ni–MCM-41 catalysts. When the Co content was 1%, a conversion of 88% and selectivity of 87% was achieved.

The Ni–Co alloy confined within MCM-41 improved dispersibility and the stability of Ni.     

Catalytic performance and deactivation of Ni/MCM-41 catalyst in the hydrogenation of pure acetylene to ethylene

Ni/MCM-41 catalysts were prepared by an impregnation method for acetylene hydrogenation to ethylene based on the calcium carbide acetylene route. X-ray diffraction and transmission electron microscopy indicated that Ni was uniformly dispersed on the support. Temperature-programmed reduction and X-ray photoelectron spectroscopy demonstrated a strong interaction between Ni and MCM-41, and Ni(0) and Ni(ii) coexisted in the catalyst. We optimized the catalytic activity by optimizing the Ni loading and reaction conditions including temperature, space velocity, and hydrogen/acetylene ratio. The acetylene conversion reached 100%, the ethylene selectivity reached 47%. Additionally, we tested the catalyst stability; the acetylene conversion was maintained at 100% for 25.73 h and was then rapidly reduced. ICP, TEM, FT-IR, thermogravimetric analysis and BET were used to investigate the reasons for catalyst deactivation; it was found that green oil deposition on the catalyst surface was the main reason for the catalyst deactivation.

Ni/MCM-41 catalysts were prepared by an impregnation method for acetylene hydrogenation to ethylene based on the calcium carbide acetylene route.     

SiO2 thin film growth through a pure atomic layer deposition technique at room temperature

In this study, less contaminated and porous SiO₂ films were grown via ALD at room temperature. In addition to the well-known catalytic effect of ammonia, the self-limitation of the reaction was demonstrated by tuning the exposure of SiCl₄, NH₃ and H₂O. This pure ALD approach generated porous oxide layers with very low chloride contamination in films. This optimized RT-ALD process could be applied to a wide range of substrates that need to be 3D-coated, similar to mesoporous structured membranes.

In this study, less contaminated and porous SiO₂ films were grown via ALD at room temperature.     

Effect of reduction temperature on the structure and hydrodesulfurization performance of Na doped Ni2P/MCM-41 catalysts

The removal of sulfur compounds from petroleum is increasingly important because of the environmental pollution caused by sulfur compounds. In this work, Na doped Ni₂P/MCM-41 catalysts were successfully prepared, and their hydrodesulfurization (HDS) performances were assessed using dibenzothiophene (DBT) as a model molecule. Moreover, the effects of reduction temperature (450–600 °C) on the structure and HDS performance of the Ni₂P/Na-MCM-41 catalysts were studied. Results showed that: (a) the reduction temperature of the catalyst could be as low as 450 °C due to Na doping, which is about 200 °C lower than that of the conventional temperature-programmed reduction method (650–1000 °C); (b) increasing the reduction temperature lead to an increase in the diameter of Ni₂P particles, which was demonstrated by size distribution analysis; (c) the HDS performance of the Ni₂P/Na-M41-T catalysts increases with reduction temperature and 99.2% DBT conversion was observed for Ni₂P/Na-M41-600, whereas the hydrogenation route of the catalysts decreased with increasing the reduction temperature, which indicates the lower reduction temperature favored the direct desulfurization pathway (DDS).

The removal of sulfur compounds from petroleum is increasingly important because of the environmental pollution caused by sulfur compounds.     

Equivalence of difluorodichloromethane (CFC-12) hydrolysis catalyzed by solid acid(base) MoO3(MgO)/ZrO2

In this paper, a solid acid(base) MoO₃(MgO)/ZrO₂ was prepared for the catalytic hydrolysis of difluorodichloromethane (CFC-12). The effects of the catalyst preparation method, calcination temperature, and hydrolysis temperature on the conversion rate of CFC-12 were studied. The catalysts were characterized by XRD, N₂ isotherm adsorption desorption, NH₃-TPD, and CO₂-TPD. Meanwhile, the equivalence of the catalytic activity of MoO₃(MgO)/ZrO₂ for CFC-12 was studied. Research shows that the solid acid MoO₃/ZrO₂ and solid base MgO/ZrO₂ catalyzed hydrolysis of CFC-12 is equivalent; the solid acid MoO₃/ZrO₂ is calcined at 600 °C for 3 h and the solid base MgO/ZrO₂ is calcined at 600 °C for 6 h (co-precipitation) and 700 °C for 6 h (impregnated) at a catalytic hydrolysis temperature of 300–400 °C and CFC-12 concentration of 4%. The catalytic hydrolysis products obtained were CO, HCl, and HF, and the CFC-12 conversion rate almost reached 100%.

In this paper, a solid acid(base) MoO₃(MgO)/ZrO₂ was prepared for the catalytic hydrolysis of difluorodichloromethane (CFC-12).     

Performance enhancement of a polydimethylsiloxane membrane for effective n-butanol pervaporation by bonding multi-silyl-functional MCM-41

In the current work, MCM-41/polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) was prepared for effective n-butanol pervaporation from a model aqueous solution. In order to improve the compatibility between MCM-41 and PDMS, different types of silane coupling agents including n-propyltrimethoxysilane (PTMS), n-octyltrimethoxysilane (OTMS), n-dodecyltrimethoxysilane (DTMS) and n-hexadecyltrimethoxysilane (HDTMS) were used to modify the MCM-41. The results showed that the highest n-butanol separation performance was achieved by bonding 20 wt% of PTMS-modified MCM-41 with PDMS. Under these conditions, total flux of 1476 g m⁻² h⁻¹ was obtained when separating a 1.5 wt% n-butanol aqueous solution at 55 °C. The total flux increased by nearly 40% compared to the pure PDMS membrane with no obvious changes of the n-butanol separation factor at the same time. The curing process of the casting solution was also significantly improved after MCM-41 modification.

The compatibility and total flux of a polydimethylsiloxane membrane were significantly improved by bonding multi-silyl-functional MCM-41.     

A template free protocol for fabrication of a Ni(ii)-loaded magnetically separable nanoreactor scaffold for confined synthesis of unsymmetrical diaryl sulfides in water

In the present report, an environmentally benign magnetically recoverable nickel(ii)-based nanoreactor as a heterogeneous catalyst has been developed via a template free approach. The catalytic performance of the synthesized catalyst is assessed in the confined oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides under aerobic conditions. The salient features of our protocol include oxidant- and ligand-free conditions, use of water as a green solvent, room temperature and formation of nitrogen and water as the only by-products. Moreover, a broad range of functional groups are tolerated well and provide the corresponding diaryl sulfides in moderate to good yields. Moreover, the heterogeneous nature of the catalyst permits facile magnetic recovery and reusability for up to seven runs, making the present protocol highly desirable from industrial and environmental standpoints.

An environmentally benign nickel(ii)-based magnetic nanoreactor has been developed for oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides in water at room temperature.     

Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as “O” source and for the regeneration of the photocatalyst.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature.     

Effect of lattice mismatch on film morphology of the quasi-one dimensional conductor K0.3MoO3

High quality epitaxial thin films of the quasi-one dimensional conductor K_0.3MoO₃ have been successfully grown on SrTiO₃(100), SrTiO₃(110), and SrTiO₃(510) substrates via pulsed laser deposition. Scanning electron microscopy revealed quasi-one dimensional rod-shaped structures parallel to the substrate surface, and the crystal structure was verified by using X-ray diffraction. The temperature dependence of the resistivity for the K_0.3MoO₃ thin films demonstrates a metal-to-semiconductor transition at about 180 K. Highly anisotropic resistivity was also observed for films grown on SrTiO₃(510).

High quality epitaxial thin films of the quasi-one dimensional conductor K_0.3MoO₃ have been successfully grown on SrTiO₃(100), SrTiO₃(110), and SrTiO₃(510) substrates via pulsed laser deposition.     

Facile synthesis of MoO2/CaSO4 composites as highly efficient adsorbents for congo red and rhodamine B

A novel rod-shaped MoO₂/CaSO₄ composite was prepared by using hexa-ammonium molybdate and flue gas desulfurization gypsum via a simple mixed-solvothermal route. In this composite, CaSO₄ matrices are decorated with MoO₂ nanoparticles, and non-structural mesopores are formed via particle packing. Moreover, it displays an excellent adsorption capability towards anionic congo red (CR) and cationic rhodamine B (RhB). The adsorption quantities per unit mass and removal efficiencies of the two dyes are significantly influenced by adsorbent dose, solution pH, and temperature. The adsorption isotherm data can be best fitted by the Langmuir model, and the calculated maximum adsorption quantities at 303.5 K are 853.54 mg g⁻¹ for CR and 86.38 mg g⁻¹ for RhB, respectively, which are superior to other common adsorbents. The corresponding kinetic data can be well matched with the pseudo-second-order model. Additionally, the CR adsorption is an exothermic process, while the RhB adsorption is an endothermic process. Both of them are multi-step chemisorption processes influenced by surface adsorption and intra-particle diffusion. This MoO₂/CaSO₄ composite can be applied as an alternative adsorbent for removing organic dyestuffs from printing and dyeing wastewater.

A new kind of rod-shaped MoO₂/CaSO₄ composite, in which MoO₂ nanoparticles are supported on the surface of CaSO₄ matrices, was prepared via a mixed-solvothermal method for efficient removal towards congo red and rhodamine B.     

Dimensionless evaluation and kinetics of rapid and ultradeep desulfurization of diesel fuel in an oscillatory baffled reactor

The oxidative desulfurization (ODS) of dibenzothiophene in diesel fuel cut using a homogeneous liquid catalytic system in a novel reactor is presented. Hydrogen peroxide was the oxidizing agent and acetic acid was the liquid catalyst. The oxidation process was conducted in a meso-oscillatory baffled reactor (“mesoOBR”) under mild operating conditions: atmospheric pressure, and 60 to 80 °C. The reactor was operated over a range of residence times (1–3 min), and frequencies and amplitudes of oscillation, leading to oscillatory Reynolds numbers in the range 64–383, and net flow Reynolds numbers in the range 5 to 16. The results showed that dibenzothiophene (DBT) removal in the OBR was significantly higher than in conventional processes under the same conditions (pressure of 1 atm and temperature near room temperature). The maximum DBT conversion was 94%, which was achieved in 3 min at 4 Hz and 6 mm amplitude. A significant improvement in the removal efficiency of DBT was achieved in OBR within only 3 minutes compared to previous studies, which required at least a half-hour reaction time to achieve the same or less removal efficiency. A reaction kinetic model was developed using the optimum experimental results achieved in the OBR. The apparent reaction order was 1, with significantly low apparent activation energies (24.7–29.0 kJ mol⁻¹).

The oxidative desulfurization (ODS) of dibenzothiophene in diesel fuel cut using a homogeneous liquid catalytic system in a novel reactor is presented.     

Solvent-free hydrogenation of cyclohexene over Rh-TUD-1 at ambient conditions

Rhodium nanoparticles (≈3–5 nm) were incorporated into the 3D mesoporous TUD-1 material by using sol–gel technique. The prepared catalyst shows high activity in the liquid phase conversion of cyclohexene to cyclohexane at room temperature (298 K), 1 atm H₂ pressure, and under solvent-free conditions. Rhodium nanoparticles exhibited high stability, reusability and negligible leaching.

Total conversion of cyclohexene to cyclohexane was achieved in a liquid phase hydrogenation reaction at room temperature, 1 atm H₂ pressure and solvent-free system.     

Preparation of CaMgAl-LDHs and mesoporous silica sorbents derived from blast furnace slag for CO2 capture

High volume blast furnace slag (BFS) resulting from iron-making activities has long been considered a burden for the environment. Despite considerable research efforts, attempts to convert BFS into high value-added products for environmental remediation are still challenging. In this study, calcium–magnesium–aluminium layered double hydroxides (CaMgAl-LDHs) and ordered mesoporous silica material (MCM-41) sorbents were simultaneously synthesized from BFS, and their CO₂ adsorption performance was evaluated. Calcium (Ca), magnesium (Mg) and aluminium (Al) were selectively extracted from BFS using hydrochloric acid. Leaching conditions consisting of 2 mol L⁻¹ acid concentration, 100 °C leaching temperature, 90 min leaching time and a solid-to-liquid ratio of 40 g L⁻¹ achieved a high leaching ratio of Ca, Mg and Al at 88.08%, 88.59% and 82.27%, respectively. The silica-rich residue (SiO₂ > 98.6 wt%) generated from the leaching process could be used as a precursor for MCM-41 preparation. Chemical composition, surface chemical bonds, morphology and textural properties of the as-synthesized CaMgAl-LDHs and MCM-41 sorbents were determined. Both the CaMgAl-LDHs and MCM-41 sorbents were found to be thermally stable and exhibited comparable adsorption uptake and rates over 20 CO₂ adsorption/desorption cycles. This work demonstrated that a total solution for the utilisation of BFS can be achieved and the resulting valuable products, i.e. CaMgAl-LDHs and MCM-41 are promising sorbents for CO₂ capture.

A total solution for the utilisation of BFS can be achieved and the resulting valuable products CaMgAl-LDHs and MCM-41 are promising sorbents for CO₂ capture.