•Confined space synthesis of hierarchical SAPO-34 zeolite with a three-dimensionally ordered mesoporous-imprinted structure.•The primary spherical elements of 3DOm-i SAPO-34 were designed to be 20, 40, and 80 nm.•The ordered mesopore sizes of 3DOm-i SAPO-34 were precisely tuned from 5.5 to 13.0 nm.•3DOm-i SAPO-34 enhanced the catalyst lifetime and favored light olefin productions.Hierarchical SAPO-34 zeolites with three-dimensionally ordered mesoporous-imprinted structure (3DOm-i SAPO-34) were first confined synthesized within three-dimensionally ordered mesoporous carbons by multiple hydrothermal (MHT) treatments. With perfect structure replication, the obtained 3DOm-i SAPO-34 zeolite particles exhibited unique ordered structures consisting of primary spherical elements of sizes determined by mesopore cages of the corresponding carbon templates, and the sizes of mesopores constituted by the adjacent spherical elements can be precisely tuned from 5.5 to 13.0 nm by varying the 3DOm carbon. The as-synthesized hierarchical 3DOm-i SAPO-34 catalysts showed superior catalytic performance in the MTO reaction with prolonged catalytic lifetime and significant improvement of selectivity for light olefins (ethylene and propylene) compared to the conventional microporous SAPO-34.Download high-res image (375KB)Download full-size image

•K2CO3/carbon hybrid was used as a catalyst of methane decomposition.•Co-production of hydrogen and fibrous carbon was obtained by methane decomposition.•K2CO3 plays a positive role on methane activation and conversion.•The oxygen transfer from K2CO3 may help formation and growth of the fibrous carbon.Methane decomposition was conducted by using K2CO3/carbon hybrids as the catalysts, and hydrogen-rich gas (with hydrogen content of about 87%) and fibrous carbons can be simultaneously obtained together with high and stable methane conversion (up to about 90% at 850 °C). Effects of K2CO3 on methane conversion, hydrogen content and fibrous carbons were investigated by changing the reaction temperature and space velocity. The results indicate that K2CO3 can greatly promote methane activation and conversion, taking responsibility for the continuous formation of CO and a trace of CO2. The oxygen transfer from K2CO3 probably provides convenience for the formation and growth of fibrous carbons.

•Ni/SiO2 catalyst was prepared via ammonia-assisted impregnation using amorphous porous SiO2 as support.•Anchored Ni2+ on the surface of SiO2 and Ni-containing phyllosilicates (PS) formed in the process of impregnation.•The catalyst possessed high nickel dispersion and strong metal-support interaction.•The catalyst showed improved activity and stability in syngas methanation.Ni/SiO2 catalyst was prepared via ammonia-assisted impregnation using amorphous porous SiO2 as support. The process of the ammonia-assisted impregnation was analyzed and the catalyst was attempted for syngas methanation. X-ray diffraction, infrared radiation and UV–vis analysis demonstrated two kinds of Ni species with less water formed after dried: the formation of Ni-containing phyllosilicates (PS) and the anchored Ni2+ on the surface of SiO2 derived from adsorption of [Ni(NH3)6]2+. X-ray diffraction and temperature programmed reduction together with X-ray photoelectron spectroscopy verified the above two Ni species induced the formation of Ni-containing PS and highly dispersed NiO strongly interacting with SiO2 after calcination. NiO aggregation in the process of calcination and metal Ni sintering during further reduction were effectively suppressed. The as-prepared Ni/SiO2 catalyst with high nickel dispersion and strong metal-support interaction showed improved activity and better stability in syngas methanation.

•Carbons were used as catalysts or catalyst supports in methane decomposition.•Effects of the operating parameter and the catalyst characteristics were discussed.•Potential origin of the activity, deactivation and regeneration were outlined.•Perspectives and challenges in use of carbon catalysts for CMD were summarized.Hydrogen and carbon materials are two promising research topics in the field of environmentally benign energy and material science, respectively. Hydrogen production by methane decomposition can avoid the formation of COx during the fossil fuel life cycle, paving the route for the development of a low-carbon hydrogen economy. The development of state-of-the-art catalysts plays a crucial role in efficient methane conversion for co-production hydrogen and nanocarbons by catalytic methane decomposition (CMD), and considerable effort has been made to develop various carbon-based catalysts in this field. This work provided a critical review on the theoretical and technological background of CMD over carbon-based catalysts, and summarized the recent research progress on the diverse commercial (i.e., activated carbon, carbon black, graphite, carbon nanotubes, carbon nanofibers, etc.) or non-commercial carbon materials (including mesoporous carbon, hierarchical porous carbons, heteroatom doped carbon, carbon supported catalysts, and so on.) as catalysts or catalyst supports and their applications in CMD. The process descriptions along with operating parameters of CMD (such as reaction temperature, pressure, space velocity, feedstock purity, reactor type and material) and the catalyst characteristics (such as preparation method and conditions, catalyst type and particle size, textural properties and surface chemistry) were discussed. Additionally, potential origin of the catalytic activity, microscopic understanding on the catalyst deactivation and regeneration, perspectives and challenges were also outlined.

In the present work, the effect of pre-calcination on carbonation conversion and cyclic stability of modified CaO-based sorbent was investigated by thermogravimetric analyzer (TGA). The modified CaO-based sorbents with CaAc2 as precursor were respectively doped with different elements (Mg, Al, Ce, Zr and La). The specific surface area, pore volume and pore size distribution were tested by N2 isothermal adsorption measurements. The phase compositions of sorbents were characterized by X-ray diffraction (XRD). The results showed that the cyclic stabilities of the sorbents were improved by pre-calcination. The pre-calcination was conducted at 900 °C for 5 h in air by the muffle furnace. With pre-calcination, the cyclic stabilities of sorbents could be as high as 96% after 22 cycles, such as CaO-Al, CaO-Ce and CaO-La. After contact with air, the carbonation conversions of spent sorbents with pre-calcination suddenly increased by about one-sixth due to the change of channel structure by hydration. Both the cyclic stability of sorbent and the durability of reactivation were related to the structural stability of sample, especially the stability of mesopores between 2 nm and 5.5 nm. The present work also provided an easy and low-cost method for reactivating the spent CaO-based sorbents.Download high-res image (175KB)Download full-size image

•The aromatization of CH4-CO2 mixtures were tested in a flow fluidized-bed reactor.•Mg-Mo/ZSM-5 improved both the catalytic activity and the selectivity to benzene.•Mg-Mo/HZSM-5 inhibits carbon deposition during the aromatization.•The introduction of Mg likely favored the generation of Mo2C species.A series of metal-modified (i.e., Fe or Mg) Mo/ZSM-5 were prepared by the impregnation method and subsequently tested in the aromatization of CH4-CO2 mixtures in a continuous flow fluidized-bed quartz reactor. Mg modification improved both the catalytic activity (9.7 vs. 12.3% conversion) and the selectivity to benzene (65.7 vs. 68.4%) while inhibiting carbon deposition (13.9 vs 10.1% carbon deposited, as determined by thermogravimetry, TG) during the dehydroaromatization of methane in the presence of CO2. SEM confirmed that the carbon species deposited over Mo/HZSM-5 and Fe-Mo/HZSM-5 catalysts were mainly carbon nanotubes. In contrast, carbon nanotubes were not detected over Mg-Mo/HZSM-5. The TG profiles and the XPS spectra revealed that the introduction of Mg likely favored the generation of Mo2C species which are considered active sites for methane dehydroaromatization. The present work provides a strategy for greatly improving the catalytic performance in the methane dehydroaromatization in the presence of CO2.Download full-size image

CaO-based sorbent is considered to be a promising candidate for capturing CO2 at high temperature. However, the adsorption capacity of CaO decreases sharply with the increase of the carbonation/calcination cycles. In this study, CaO was derived from calcium acetate (CaAc2), which was doped with different elements (Mg, Al, Ce, Zr and La) to improve the cyclic stability. The carbonation conversion and cyclic stability of sorbents were tested by thermogravimetric analyzer (TGA). The sorbents were characterized by N2 isothermal adsorption measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the cyclic stabilities of all modified sorbents were improved by doping elements, while the carbonation conversions of sorbents in the 1st cycle were not increased by doping different elements. After 22 cycles, the cyclic stabilities of CaO–Al, CaO–Ce and CaO–La were above 96.2%. After 110 cycles, the cyclic stability of CaO–Al was still as high as 87.1%. Furthermore, the carbonation conversion was closely related to the critical time and specific surface area.Download high-res image (282KB)Download full-size image

A facile approach was developed for the preparation of nano-sized HZSM-5 with a hierarchical mesoporous structure by adding imidazole into conventional zeolite synthesis precursor solution. The physicochemical properties of modified HZSM-5 were characterized by X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), NH3-temperature-programmed desorption (NH3-TPD) and pyridine adsorption infrared spectroscopy (Py-IR). The coke in spent catalysts was characterized by thermogravimetry (TG). The results showed that hierarchical HZSM-5 zeolites with excellent textural properties, such as abundant porous structure, uniform particle size and suitable acidity, could be synthesized by the recipe of one-pot synthesis routes. Moreover, the obtained HZSM-5 exhibited higher selectivity of total aromatics as well as longer lifetime in the catalytic conversion of methanol to aromatics, comparing with conventional HZSM-5. It is expected that the synthesis approach demonstrated here will be applicable to other zeolites with particular textural properties and controllable particle sizes, facilitating the emergence of new-type porous materials and their related applications in catalysis and separation.The modification of imidazole was a promising way for the synthesis of MFI zeolites which showed excellent catalytic performance in MTA reactions. Download high-res image (165KB)Download full-size image

•The 2:1 urea-succinic acid cocrystals were generated by a simple sublimation apparatus.•The development of supersaturations in vapor crystallization was also discussed.•This work showed sublimation is a promising method for cocrystallization.The aim of this study is to introduce a sublimation method for preparing cocrystals. The 2:1 urea-succinic acid cocrystals were generated by a simple sublimation apparatus, analyzed by Powder X-ray Diffraction (PXRD), Transmission Fourier Transform Infrared (FTIR) and Differential Scanning Calorimetry (DCS). The role of supersaturations in vapor crystallization was also discussed in detail. This work showed sublimation was a promising method for cocrystallization.

•Separation of low temperature coal tar with silica-gel column chromatography was carried out.•Coal tar was separated into eight fractions with a binary eluent of n-hexane and ethyl acetate.•Pyrenol is the largest molecular weight phenols in low temperature coal tar.•The solvent extraction–column chromatography (SECC) device has been designed.•SECC could realize the separation of neutral oil, pitch and crude phenol from coal tar.The heavy tar (H-tar) of low temperature coal tar was collected from a low temperature carbonization plant in Shanbei. H-tar was separated into eight fractions by silica-gel column chromatography (SGCC) with a binary eluent of n-hexane and ethyl acetate (EA). A series of alkanes (C14–C28), phenolic compounds and aromatic nitrogen species were fractionated from H-tar by SGCC and analyzed by gas chromatography–mass spectrometry (GC–MS). Most of the GC–MS detectable phenolic compounds are phenol, cresol, xylenol, C3–C4 alkyl phenols, indanols, naphthalenols, methyl naphthalenols, benzenediols, fluorenols, phenanthrols and pyrenol, among which cresol is the most abundant one and pyrenol is the largest molecular weight one. According to the change rule of phenolic compounds with the polarity of eluting solvents, the solvent extraction–column chromatography (SECC) device and crude phenol recovery processing have been designed and developed, which could realize the separation of neutral oil, pitch and crude phenol from low temperature coal tar.

•Negative ions of CO2 and H2O have been used for CO2 reduction to produce ethanol.•The CO2 conversion could be about 16% at 1 atm and 105 °C.•The molar yield of both ethanol and methanol could achieve 11.9% at 4 atm.•The production of ethanol by negative-ion method could lead to energy storage.Direct production of useful fuel from the emitted carbon dioxide has been one of major challenges in industries. We here report a novel approach in which ethanol could simply be synthesized under negative DC corona discharge at 1 atm and 105 °C. The experimental results have shown that CO2 and H2O could be reduced mainly into ethanol with yield of 4.7% without applying any metal catalyst. And with increase of total feeding pressure of gases, the yield appears to rise. The mechanism of electron attachment on those gaseous molecules creating accelerated anions might be the key of CO2 and H2O reduction reaction. This finding also implies that it might be feasible to use of negative corona discharge and CO2 as only carbon source with steam as only source of hydrogen to produce energy-dense ethanol fuel, also possibly leading to electric energy storage.

Catalyst surface modification with supported metals is an efficient way of controlling coal pyrolysis and enhancing the production of high value-added chemicals. In this work, zeolite NaX and CoOx-, MoOx-, and CoOx–MoOx-supported NaX catalysts were prepared and characterized by transmission electron microscopy, scanning electron microscopy-energy dispersive spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller analysis. Huang Tu Miao (HTM) coal, a typical long flame coal in Western China, was selected as the testing material. The pyrolysis of HTM coal was conducted in 5% H2/N2 atmosphere, and the volatiles were examined by thermogravimetric (TG) Fourier-transform infrared (FTIR) spectroscopy. The addition of zeolite NaX significantly enhanced the production of CO, CH4, and aromatic and aliphatic hydrocarbons, and dramatically reduced the generation of CO2. These results are in contrast to the transition metal oxide-supported HZSM-5 in our previous report. In addition, the pyrolysis product profiles, expressed by FTIR absorbance, were similar for the HTM-NaX and HTM-HZSM-5 mixtures but different for the HTM-transition-metal-incorporated zeolite NaX and HZSM-5 mixtures. This result may imply differences in pyrolysis mechanism. Catalyst composition, pore size, and acidity may play key roles in pyrolysis. The pyrolysis kinetics of HTM coal was determined by the single reaction, first-order model. The lowest activation energy of the secondary degasification stage was observed in CoOx–MoOx/NaX.Highlights► Catalytic pyrolysis of HTM coal was conducted over NaX and MOx/NaX catalysts. ► Catalyst composition, pore size and acidity may play key roles in the pyrolysis. ► The lowest activation energy of 2nd degasication was observed on CoOx–MoOx/NaX. ► The pyrolysis mechanism may be different for the HTM-NaX and HTM-HZSM-5 mixtures.

The solubilities of l-glutamine in mixed solvents (ethanol + water, acetone + water) were determined at temperatures between 278 K and 313 K. The solubilities of l-glutamine in mixed solvents (water + ethanol, water + acetone) are a function of temperature, increasing with an increase in temperature. Pure water has a high dissolving power. The experimental data were correlated with the Apelblat model. The calculated values of Apelblat model were found to show a fine representation of the experimental data. Then the dissolution enthalpy and entropy of l-glutamine were predicted from the solubility data using van’t Hoff equation. The dissolution enthalpy and entropy of l-glutamine in water predicted from the solubility data is less than that in mixed solvents.Highlights► The solubilities of l-glutamine in mixed solvents (ethanol + water, acetone + water) were measured. ► It increases with an increase in temperature. ► Pure water has a high dissolving power. ► The calculated solubility sets a good coherence with the experimental values. ► The dissolution enthalpy and entropy were predicted using van’t Hoff equation.

Five Chinese coals were subjected to pyrolysis by thermogravimetry (TG). The investigated pyrolysis conditions included pyrolysis atmospheres (N2 and 10% H2/N2) and catalysts (MoS2 and ZnCl2) with different amounts (0.5, 1.0, 2.0, 5.0, and 10%). The existence of hydrogen improved the final conversion and reduced the reaction temperature by different degrees. With the addition of catalysts, the maximal reaction rate in the hydropyrolysis process was increased for all coals, except Shaotong coal. The optimal catalytic amount for each coal was determined by the final conversion. MoS2 was more effective on the increase of the total conversion than ZnCl2, while ZnCl2 was more effective on reducing the peak temperature of secondary devolatilization. Finally, the kinetics results showed that the activation energy would be lower in the catalytic hydropyrolysis process than that in the non-catalytic run. Tongchuan coal was subjected to pyrolysis in a fixed bed. The results showed that ZnCl2 and MoS2 improved the conversion in different ways. ZnCl2 increased the yield of liquid but has little effects on the yield of benzene, toluene, and xylene (BTX), while MoS2 increased the yield of BTX obviously in hydropyrolysis.

>300 °C fraction obtained by distillation of heavy tar of low temperature coal tar was reacted with paraformaldehyde. After reaction, toluene soluble (TS-tar) and toluene insoluble (TIS-tar) fractions were collected. Their structures were confirmed by gas chromatography–mass spectroscopy (GC–MS), gel permeation chromatography (GPC) and Fourier transformed infrared (FTIR). The degradations under nitrogen atmosphere of >300 °C fraction and TIS-tar were investigated by thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR). Based on the above analyses, polymers were generated and the carbonization yields were increased by polymerization reaction. The degradation process of TIS-tar was divided into two stages, 118–248 °C and 248–700 °C. In the pyrolysis process of >300 °C fraction, CO has no significant absorbency for infrared at 2060–2240 cm−1, but there are obvious absorption peaks in TIS-tar. Polymerization reaction of paraformaldehyde and compounds with carboxyl, short-chain fatty and ester group in >300 °C fraction generates polymers and fixes these compounds.Highlights► Reaction of >300 °C fraction of low temperature coal tar with paraformaldehyde was carried out. ► Reaction products were separated into toluene-soluble (TS-tar) and toluene-insoluble (TIS-tar). ► TS-tar and TIS-tar were analyzed by GC–MS and TG-FTIR. ► Polymerization of coal tar fractions and aldehydes fixes complex phenols and PAH. ► Coal tar fractions preliminary were separated and composition was obtained.

We here report that by using electronegative gas of iodine and CO2 under negative corona discharge, tetraiodomethane could be synthesized at 70 °C and 1 atm without any catalyst, despite thermodynamically infeasible at ambience without electron discharge. The conversion of carbon dioxide reached 88.71 % at a gas flow rate of 0.06 L/min and a discharge frequency of 9.608 kHz. The anion-involved CO2 reduction process could be implemented efficiently under mild conditions, avoiding high temperature and high pressure.

Urea synthesis, currently the largest use of carbon dioxide in organic synthesis, is conventionally operated at high pressure and high temperature. Here, we report for the first time that urea forms at atmosphere and ambient temperatures by negative corona discharge in gas phase. The conversion of CO2 and yields of a solid mixture of urea and ammonium carbamate, which was identified by the 13C NMR spectrum, rise with reducing temperatures and increasing molar ratios of NH3/CO2 and discharge frequencies. The conversion of carbon dioxide was found to be 82.16 % at 20 °C and 1 atm with a molar flow ratio of n(NH3)/n(CO2) of 2.5. High pressure and high temperature as energy inputs are not necessary.

The photosensitized semiconductor catalysts – TiO2 nanotubes – were modified by functionalized supramolecular sensitizers: zinc(II)/copper(II)/cobalt(II) porphyrin-ruthenium(II) polypyridly complexes and photocatalytic activity of the modified TiO2 nanotubes were investigated through the reduction of CO2 aqueous solution as a probe reaction under UV–vis light. The diverse photoreduction properties of the catalysts resulted from the different polypyridly derivatives: 2,2′-bipyridyl, 1,10-phenanthroline, and 2,2′-bipyridyl-4,4′-dicarboxylate. The different central coordinated metal ions in the porphyrin ring influenced the photocatalytic efficiency of the sensitized-TiO2 system at the same time. A possible mechanism for the photocatalytic reduction was also proposed in this paper.Graphical abstractThe photosensitized semiconductor catalysts – TiO2 nanotubes – were modified by functionalized supramolecular sensitizers: zinc(II)/copper(II)/cobalt(II) porphyrin-ruthenium(II) polypyridly complexes and photocatalytic activity of the modified TiO2 nanotubes were investigated through the reduction of CO2 aqueous solution as a probe reaction under UV–vis light. The diverse photoreduction properties of the catalysts were resulted from the different polypyridly derivatives: 2,2′-bipyridyl, 1,10-phenanthroline, and 2,2′-bipyridyl-4,4′-dicarboxylate. The different central coordinated metal ions in porphyrin ring influence the photocatalytic efficiency of the sensitized-TiO2 system at the same time. A possible mechanism of the photocatalytic reduction was also proposed in this paper.Highlights► Novel supramolecular photosensitizers TiO2 nanotube catalysts were synthesized. ► The TiO2 nanotube photocatalytic in CO2 reduction have not been report at present. ► All the photosensitizers enhanced the catalytic efficiency of bare TiO2 nanotube. ► The modified TiO2 catalysts displayed good methanol selectivity. ► A possible mechanism of the photocatalytic reduction was proposed in this paper.

The heavy tar (H-tar) of low temperature coal tar was collected from a low temperature carbonization plant in Shanbei. H-tar was extracted with petroleum ether (PE) under ultrasonic irradiation and separated into PE soluble and insoluble fractions. Then, the PE insoluble fraction was extracted in a Soxhlet extractor with PE and methanol (MeOH), respectively. PE extract, PE residue, MeOH extract, and MeOH residue were obtained. PESE (PE soluble fraction and PE extract) and MeOH extract were examined by gas chromatography−mass spectrometry (GC-MS). GC-MS analysis of PESE shows considerable alkanes and extensive series of phenols, naphthalenes, fluorenes, benz[a]anthracene, chrysene, etc. Particularly, the content of methyl phenol is about 9.0%. No GC-MS detectable species are found in MeOH extract. So, additional research will focus on PE residue. The pyrolysis behavior of PE residue was investigated by using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR). The results indicate that the release of volatiles takes place mainly between 110 and 425 °C and the maximum mass loss rate occurs at 315 °C. The main products in the whole process are CO2, phenols, H2O, saturated hydrocarbons, aromatic compounds, anhydride compounds, oxygen heterocycles, pyridines, etc. But there is no significant peak of CO. The compounds of alkanes, phenols, heterocyclic compounds, and oxygen-containing heterocyclic compounds in PE residue can be also detected. PE residue semicoke (the products of PE residue after TG) and PE residue were estimated by FTIR. PE residue is mainly composed of phenols, aliphatics, and aromatics. The analyses indicate the high degree and polycyclic aromatic structure of PE residue semicoke.

The Intalox metal tower packing was used to simulate an industrial relevant extractive distillation column for purifying azeotropic multicomponent mixture. In order to explain the inconsistencies in the modeling of transfer process in nonideal multicomponent distillation column, a method was developed with equilibrium stage models (EQ) and non-equilibrium model (NEQ) incorporated with Maxwell-Stefan diffusion equations in the framework of AspenONE(r) simulator. Dortmund Modified UNIFAC (UNIFAC-DMD) thermodynamic model was employed to estimate activity coefficients. In addition, to understand the reason for the diffusion against driving force and the different results by EQ and NEQ models, explicit investigations were made on diffusion coefficients, component Murphree efficiency and mass transfer coefficients. The results provide valuable information for basic design and applications associated with extractive distillation.