Due to their versatility, nontoxicity, and low cost, much attention has been paid to the fabrication of Cu(I) sites on various supports. High-temperature autoreduction is a widely used method for selective conversion of supported Cu(II) to Cu(I). However, aggregation of copper species usually takes place during autoreduction, which seriously decreases the yield of Cu(I) and compromises the activity of resultant materials. In the present study, a strategy was developed for the effective formation and dispersion of Cu(I) sites by constructing a confined space in silica nanopores, for the first time. A layer of porous silica is coated on the precursor (namely CuO-modified SBA-15) before autoreduction, and CuO is thus confined between original pore walls and newly formed silica layers. Owing to the energy barrier offered by the confined space, the dispersion degree of copper species after autoreduction is well improved. Furthermore, the yield of Cu(I) can reach ∼82% for the samples coated with silica, which is obviously higher than that for the sample without a silica layer (∼54%). More importantly, abundant pores with a uniform size of ∼2.5 nm are successfully generated on the silica layer under the direction of cetyltrimethylammonium bromide (CTAB). This endows the resultant materials with active sites highly accessible to guest molecules. The materials were also applied to the adsorption of CO by using π-complexation between CO and Cu(I) sites. The results show that these materials exhibit good performance for selective adsorption of CO from H2, CH4, and N2, which is apparently better than the material without a silica layer with regard to both capacity and selectivity.

Selective reduction of supported CuO to Cu2O was realized using the strategy of vapor-induced reduction, in which HCHO/H2O vapor diffuses into the pores of the support and interacts with predispersed CuO. This new strategy allows the fabrication of supported cuprous sites at much lower temperatures within a short time, avoids the formation of Cu(0) with a Cu(I) yield of nearly 100%, and results in materials with good adsorption performance, which is impossible to achieve by conventional methods.

Great attention has been paid to the development of mesoporous solid superbases due to their versatile catalytic activity under mild conditions. In this paper, a dualcoating strategy was designed to generate superbasicity on mesoporous silica SBA-15 by precoating ZrO2 prior to the loading of base precursor (KNO3). The ZrO2 interlayer performs two functions by enhancing the guest–host interactions to promote the decomposition of KNO3 at low temperatures, and by improving the alkali-resistance of the siliceous host, which simultaneously overcomes two weaknesses of mesoporous silicas. As a result, new dualcoating composites possessing both an ordered mesostructure and superbasicity were successfully fabricated. However, direct modification of SBA-15 with KNO3 results in a sample with only weak basicity and a collapsed mesostructure. Interestingly, both the amount and dispersion degree of ZrO2 play an important role in the generation of strong basicity. An intact layer can be formed on SBA-15 provided that the content of ZrO2 is higher than 30 wt% and the ammonia/water-induced hydrolysis (AIH) method is employed. The mesostructure cannot be preserved if the content of ZrO2 is lower than 30 wt% or if conventional coating methods (i.e. impregnation and grinding) are used. The obtained materials containing ZrO2 are active in heterogeneous synthesis of dimethyl carbonate (DMC) and the yield of DMC can reach 28.4%, which is obviously higher than that over the material without a ZrO2 coating (9.8%). The present strategy may open a new way for the design and synthesis of functional materials with strong basicity.

Mesoporous solid strong bases are highly promising for applications as environmentally benign catalysts in various reactions. Their preparation attracts increasing attention for the demand of sustainable chemistry. In the present study, a new strategy was designed to fabricate strong basicity on mesoporous silica by using multifunction of a carbon interlayer. A typical mesoporous silica, SBA-15, was precoated with a layer of carbon prior to the introduction of base precursor LiNO3. The carbon interlayer performs two functions by promoting the conversion of LiNO3 at low temperatures and by improving the alkali-resistant ability of siliceous host. Only a tiny amount of LiNO3 was decomposed on pristine SBA-15 at 400 °C; for the samples containing >8 wt % of carbon, however, LiNO3 can be entirely converted to strongly basic sites Li2O under the same conditions. The guest–host redox reaction was proven to be the answer for the conversion of LiNO3, which breaks the tradition of thermally induced decomposition. More importantly, the residual carbon layer can prevent the siliceous frameworks from corroding by the newly formed strongly basic species, which is different from the complete destruction of mesostructure in the absence of carbon. Therefore, materials possessing both ordered mesostructure and strong basicity were successfully fabricated, which is extremely desirable for catalysis and impossible to realize by conventional methods. We also demonstrated that the resultant mesoporous basic materials are active in heterogeneous synthesis of dimethyl carbonate (DMC) and the yield of DMC can reach 32.4%, which is apparently higher than that over the catalysts without a carbon interlayer (<12.9%) despite the same lithium content. The strong basicity, in combination with the uniform mesopores, is believed to be responsible for such a high activity.Keywords: alkali-resistance; basicity generation; carbon interlayer; guest−host redox reaction; mesoporous silica; transesterification;

An unprecedented guest–host redox strategy is developed to generate strong basicity on mesoporous silica, which breaks the tradition of thermally induced decomposition of precursors. New materials possessing ordered mesostructure, strong basicity, and excellent catalytic activity are thus successfully fabricated at a low temperature.

Deep desulfurization via π-complexation adsorption is an effective method for the selective capture of thiophenic sulfur compounds. The adsorptive desulfurization capacity of an adsorbent has been demonstrated to strongly depend on the dispersion degree of active species. In the present study, a strategy was developed to promote the dispersion of copper species by directly using as-synthesized mesoporous silica SBA-15 as a support. The results show that the confined space between template and silica walls is highly efficient in dispersing the resultant guest oxide, and unusual CuO dispersion is realized. However, severe CuO aggregation occurs on the material prepared through the conventional method based on template-free SBA-15. Interestingly, copper precursors have a significant effect on the dispersion degree of the oxide, which decreases in the order nitrate > acetate > chloride. After autoreduction, the materials are active in adsorptive desulfurization, and the desulfurization performance relates well to the dispersion degree of the oxide. The present strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in the conventional modification process, and saves time and energy. This strategy may open up an avenue for the design and synthesis of new functional materials by use of some particular micro environments.

An unusual ceria dispersion was achieved by using the confined space between template and silica walls in as-prepared mesoporous silica, for the first time. The new adsorbents exhibit high adsorptive desulfurization activity and, more importantly, excellent stability and reusability, which is impossible to realize with conventional adsorbents.

Isolated lithium sites were anchored on mesoporous silica by a molecular precursor approach at room temperature. The resultant materials exhibit ordered mesostructure, high base strength, and more importantly, a molecular-level dispersion of active sites, which are extremely desirable for catalysis and impossible to be realized by conventional methods.

Mesoporous solid superbases have high potentials for applications as environmentally benign catalysts in diverse reactions, whereas their preparation remains a challenge. In the present study, an in situ functionalization strategy was designed to fabricate mesoporous solid superbases based on the hard-templating synthetic system of mesoporous ceria. Sodium and potassium modified mesoporous ceria (NaMC and KMC) were successfully prepared, and structural and basic properties were characterized by various methods. The obtained materials exhibit well-expressed mesostructure and superbasicity with a high strength of 27.0. The basic solutions (namely NaOH and KOH aqueous solutions) play a double role by removing the silica template SBA-15 and functioning as the guests. Therefore, sodium and potassium can be coated onto mesoporous ceria formed in situ. This strategy allows the fabrication and functionalization of mesoporous ceria in one step, which avoids the destruction of mesoporous ceria in post-modification. The obtained mesoporous solid superbases also exhibit excellent catalytic performance in dimethyl carbonate (DMC) synthesis. The yield of DMC can reach 64.6% in 4 h over NaMC, which is apparently higher than those over the samples derived from post-modification (28.9%), nonmesoporous ceria (10.8%), as well as the conventional solid base magnesia (7.6%).Graphical abstractHighlights► Solid superbasic materials were fabricated based on mesoporous ceria. ► In situ generation of superbasic sites in hard-templating synthetic system. ► Flexible utilization of basic solutions to remove template and function as guests. ► Excellent basic catalytic performance in dimethyl carbonate synthesis.

A novel π-complexation adsorbent is fabricated by grafting Cu(I)-containing molecule precursors onto β-cyclodextrin. The adsorbent provides a molecular-level dispersion of Cu(I), which is particularly beneficial to the adsorptive removal of aromatic sulfur thiophene, and is impossible to be realized through the conventional thermal method.

Deep desulfurization via π-complexation adsorption is a promising method for the purification of transportation fuels. The desulfurization performance of an adsorbent has been proven to strongly depend on the dispersion extent of adsorption active species. In this paper, we report a strategy to promote the dispersion of active species CuCl on mesoporous silica SBA-15 by incorporating alumina. By use of such a strategy, properties of the host SBA-15 were successfully adjusted. The enhancement of host–guest interaction and the improvement of surface hydrophilicity were realized simultaneously. Furthermore, the solid-state ion exchange between CuCl and formed Brönsted acid sites (H+) was observed, which leads to the generation of isolated cuprous species. As a result, the dispersion of guest CuCl on the host was efficiently promoted. We also demonstrated that the obtained material, CuCl supported on SBA-15 incorporated with 10 wt % of alumina, can capture 0.240 mmol·g–1 thiophene, which is obviously higher than that over CuCl/SBA-15 (0.167 mmol·g–1). Our materials may provide a potential candidate for application in adsorptive desulfurization.

A series of Cu-containing mesoporous MCM-48 molecular sieves (Cu-MCM-48) were prepared by the direct synthesis method and used as the adsorbents for desulfurization of model fuel. The samples were characterized by X-ray power diffraction, N2 adsorption–desorption isotherms, Brunauer–Emmett–Teller specific surface area, transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and X-ray photoelectron spectroscopy. The results show that the Cu-MCM-48 adsorbent with a copper content up to 10 wt % can still retain the uniform mesoporous framework of MCM-48. The proposed direct synthesis method gives better Cu dispersion and a higher content of active component Cu+ in the support than the conventional incipient impregnation method. As a result, the desulfurization performance of these adsorbents is enhanced. The adsorption behaviors of thiophene on these molecular sieves were measured at 20 °C, and their adsorption capacities follow the order 10Cu-MCM-48 > 5Cu-MCM-48 > 10Cu/MCM-48 (synthesized by the incipient impregnation method) > 20Cu-MCM-48. The adsorption isotherms for thiophene fit the Langmuir model well.

An in situ functionalization strategy was developed in a hard template process to fabricate mesoporous solid superbases, and sodium-modified mesoporous zirconia (NaMZ) was successfully prepared. The obtained materials were characterized by various methods including XRD, TEM, N2 adsorption, IR spectroscopy, XRF, and CO2 TPD. The results show that the NaMZ materials exhibit well-defined mesostructure, tetragonal crystalline frameworks, and superbasicity with a high strength of 27.0. The NaOH solution plays a double role by removing the silica template SBA-15 and functioning as the guest. The sodium species is thus coated onto the mesoporous zirconia formed in situ. Hence, the fabrication and functionalization of mesoporous zirconia can be realized in one step, which avoids the possible structural damage of nonsiliceous mesoporous oxides in post-treatment. The stability of metastable tetragonal zirconia was found to be due to the confined space provided by the mesoporous silica template and the formation of Si–O–Zr linkages. It was also demonstrated that the NaMZ materials exhibited excellent basic catalytic performance. The turnover frequency (TOF) value on the material NaMZ-2 can reach 95.0 h–1 with 100% selectivity to the target product dimethyl carbonate, which is much higher than the value for the extensively used homogeneous catalyst CH3ONa (45.8 h–1).

A new strategy was utilized to generate strong basicity on mesoporous silica SBA-15 by precoating alumina before modification with the base precursor, potassium nitrate. The nature of the mesoporous silica host was greatly modulated by the alumina interlayer. Such an alumina interlayer plays a double role by enhancing the guest−host interaction to promote the decomposition of potassium nitrate and by improving the alkali-resistance of the mesoporous silica host. The majority of the potassium nitrate is decomposed at 690 °C on unmodified SBA-15, while the temperature decreases to 460 °C after precoating an alumina layer. Moreover, the ordered mesoporous structure of the parent, SBA-15, is well-preserved even if the supported potassium nitrate was decomposed to strongly basic potassium oxide, which is quite different from the complete destruction of the mesostructure in the absence of alumina. As a result, materials possessing both a mesoporous structure and superbasicity with a high strength of 27.0 were successfully fabricated. We also demonstrated that both the amount and the location of aluminum in the samples are of great importance for the generation of strong basicity. The content of alumina should reach as high as 20 wt %, which is necessary for the formation of an intact interlayer; thus, the silica frameworks can be well-protected after introducing strongly basic species. Also, the location of aluminum on the pores rather than in the frameworks is demanded from the point of view of mesostructure protection.

Copper species were incorporated into SBA-15 by solid-state grinding precursor with as-prepared mesoporous silica (SPA). The obtained materials (CuAS) were well-characterized by XRD, TEM, N2 adsorption, H2-TPR, IR, and TG and compared with the material derived from calcined SBA-15 (CuCS). Surprisingly, CuO up to 6.7 mmol·g−1 can be highly dispersed on SBA-15 by use of SPA strategy. Such CuO forms a smooth layer coated on the internal walls of SBA-15, which contributes to the spatial order and results in less-blocked mesopores. However, the aggregation of CuO takes place in CuCS material containing 6.7 mmol·g−1 copper, which generates large CuO particles of 21.4 nm outside the mesopores. We reveal that the high dispersion extent of CuO is ascribed to the abundant silanols, as well as the confined space between template and silica walls provided by as-prepared SBA-15. The SPA strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in conventional modification process, and saves time and energy. We also demonstrate that the CuAS material after autoreduction exhibits much better adsorptive desulfurization capacity than CuCS. Moreover, the adsorption capacity of regenerated adsorbent can be recovered completely.

AlPO4-14 molecular sieve was prepared by hydrothermal crystallization of saturated gels. The synthesized molecular sieve was characterized by X-ray diffraction and scanning electron microscopy. For the first time, the adsorption behavior of CO2 and CH4 was investigated on AlPO4-14, a neutral molecular sieve with no extra-framework cations. Adsorption isotherms of CO2 and CH4 on AlPO4-14 were examined at 273 and 300 K. Henry’s law constants and isosteric heats of adsorption of all adsorbates were determined from adsorption isotherms. It was found that CO2 was strongly adsorbed on the molecular sieve, and the selectivity of CO2/CH4 can reach as high as 21.77 at 273 K. The adsorbate−adsorbent interaction and the steric effect should be responsible for the preferential adsorption of CO2 on AlPO4-14.

Adsorbents based on metal ion-exchanged Y zeolites (with single Cu and Ce or the combined Cu−Ce) were prepared. Then, the adsorptive desulfurization properties of the adsorbents were studied by a batch method at ambient conditions through model fuels, which were the iso-octane solution of sulfur compounds, and, in some cases, with a small quantity of toluene. The results show that CuCeY not only has the high sulfur adsorption capacity similar to CuIY but also has the high selectivity for sulfur compounds similar to CeIVY. Inductively coupled plasma−atomic emission spectrometer (ICP−AES) and X-ray photoelectron spectroscopy (XPS) studies indicate that Ce can not only use the surface of zeolite effectively and disperse at the geometric position, which is unfavorable to Cu, but also accelerate the conversion of Cu2+ to Cu+ and enhance the concentration of Cu+ on the surface of the adsorbent. Therefore, CuCeY exhibits an excellent sulfur adsorption performance. The saturated CuCeY can be regenerated with a solvent consisting of 30 wt % toluene and 70 wt % iso-octane. In addition, about 90% of the sulfur adsorption capacity is recovered after regeneration.

A new type of composite adsorbents was synthesized by incorporating monoethanol amine (MEA) into β-zeolite. The parent and MEA-functionalized β-zeolites were characterized by X-ray diffraction (XRD), N2 adsorption, and thermogravimetric analysis (TGA). The adsorption behavior of carbon dioxide (CO2), methane (CH4), and nitrogen (N2) on these adsorbents was investigated at 303 K. The results show that the structure of zeolite was well preserved after MEA modification. In comparison with CH4 and N2, CO2 was preferentially adsorbed on the adsorbents investigated. The introduction of MEA significantly improved the selectivity of both CO2/CH4 and CO2/N2, the optimal selectivity of CO2/CH4 can reach 7.70 on 40 wt% of MEA-functionalized β-zeolite (MEA(40)-β) at 1 atm. It is worth noticing that a very high selectivity of CO2/N2 of 25.67 was obtained on MEA(40)-β. Steric effect and chemical adsorbate-adsorbent interaction were responsible for such high adsorption selectivity of CO2. The present MEA-functionalized β-zeolite adsorbents may be a good candidate for applications in flue gas separation, as well as natural gas and landfill gas purifications.

Adsorption isotherms of carbon dioxide (CO2), methane (CH4), and nitrogen (N2) on Hβ and sodium exchanged β-zeolite (Naβ) were volumetrically measured at 273 and 303 K. The results show that all isotherms were of Brunauer type I and well correlated with Langmuir-Freundlich model. After sodium ions exchange, the adsorption amounts of three adsorbates increased, while the increase magnitude of CO2 adsorption capacity was much higher than that of CH4 and N2. The selectivities of CO2 over CH4 and CO2 over N2 enhanced after sodium exchange. Also, the initial heat of adsorption data implied a stronger interaction of CO2 molecules with Na+ ions in Naβ. These results can be attributed to the larger electrostatic interaction of CO2 with extraframework cations in zeolites. However, Naβ showed a decrease in the selectivity of CH4 over N2, which can be ascribed to the moderate affinity of N2 with Naβ. The variation of isosteric heats of adsorption as a function of loading indicates that the adsorption of CO2 in Naβ presents an energetically heterogeneous profile. On the contrary, the adsorption of CH4 was found to be essentially homogeneous, which suggests the dispersion interaction between CH4 and lattice oxygen atoms, and such interaction does not depend on the exchangeable cations of zeolite.

An unusual ceria dispersion was achieved by using the confined space between template and silica walls in as-prepared mesoporous silica, for the first time. The new adsorbents exhibit high adsorptive desulfurization activity and, more importantly, excellent stability and reusability, which is impossible to realize with conventional adsorbents.

Due to their versatility, nontoxicity, and low cost, much attention has been paid to the fabrication of Cu(I) sites on various supports. High-temperature autoreduction is a widely used method for selective conversion of supported Cu(II) to Cu(I). However, aggregation of copper species usually takes place during autoreduction, which seriously decreases the yield of Cu(I) and compromises the activity of resultant materials. In the present study, a strategy was developed for the effective formation and dispersion of Cu(I) sites by constructing a confined space in silica nanopores, for the first time. A layer of porous silica is coated on the precursor (namely CuO-modified SBA-15) before autoreduction, and CuO is thus confined between original pore walls and newly formed silica layers. Owing to the energy barrier offered by the confined space, the dispersion degree of copper species after autoreduction is well improved. Furthermore, the yield of Cu(I) can reach ∼82% for the samples coated with silica, which is obviously higher than that for the sample without a silica layer (∼54%). More importantly, abundant pores with a uniform size of ∼2.5 nm are successfully generated on the silica layer under the direction of cetyltrimethylammonium bromide (CTAB). This endows the resultant materials with active sites highly accessible to guest molecules. The materials were also applied to the adsorption of CO by using π-complexation between CO and Cu(I) sites. The results show that these materials exhibit good performance for selective adsorption of CO from H2, CH4, and N2, which is apparently better than the material without a silica layer with regard to both capacity and selectivity.

Great attention has been paid to the development of mesoporous solid superbases due to their versatile catalytic activity under mild conditions. In this paper, a dualcoating strategy was designed to generate superbasicity on mesoporous silica SBA-15 by precoating ZrO2 prior to the loading of base precursor (KNO3). The ZrO2 interlayer performs two functions by enhancing the guest–host interactions to promote the decomposition of KNO3 at low temperatures, and by improving the alkali-resistance of the siliceous host, which simultaneously overcomes two weaknesses of mesoporous silicas. As a result, new dualcoating composites possessing both an ordered mesostructure and superbasicity were successfully fabricated. However, direct modification of SBA-15 with KNO3 results in a sample with only weak basicity and a collapsed mesostructure. Interestingly, both the amount and dispersion degree of ZrO2 play an important role in the generation of strong basicity. An intact layer can be formed on SBA-15 provided that the content of ZrO2 is higher than 30 wt% and the ammonia/water-induced hydrolysis (AIH) method is employed. The mesostructure cannot be preserved if the content of ZrO2 is lower than 30 wt% or if conventional coating methods (i.e. impregnation and grinding) are used. The obtained materials containing ZrO2 are active in heterogeneous synthesis of dimethyl carbonate (DMC) and the yield of DMC can reach 28.4%, which is obviously higher than that over the material without a ZrO2 coating (9.8%). The present strategy may open a new way for the design and synthesis of functional materials with strong basicity.

Deep desulfurization via π-complexation adsorption is an effective method for the selective capture of thiophenic sulfur compounds. The adsorptive desulfurization capacity of an adsorbent has been demonstrated to strongly depend on the dispersion degree of active species. In the present study, a strategy was developed to promote the dispersion of copper species by directly using as-synthesized mesoporous silica SBA-15 as a support. The results show that the confined space between template and silica walls is highly efficient in dispersing the resultant guest oxide, and unusual CuO dispersion is realized. However, severe CuO aggregation occurs on the material prepared through the conventional method based on template-free SBA-15. Interestingly, copper precursors have a significant effect on the dispersion degree of the oxide, which decreases in the order nitrate > acetate > chloride. After autoreduction, the materials are active in adsorptive desulfurization, and the desulfurization performance relates well to the dispersion degree of the oxide. The present strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in the conventional modification process, and saves time and energy. This strategy may open up an avenue for the design and synthesis of new functional materials by use of some particular micro environments.

Isolated lithium sites were anchored on mesoporous silica by a molecular precursor approach at room temperature. The resultant materials exhibit ordered mesostructure, high base strength, and more importantly, a molecular-level dispersion of active sites, which are extremely desirable for catalysis and impossible to be realized by conventional methods.

A novel π-complexation adsorbent is fabricated by grafting Cu(I)-containing molecule precursors onto β-cyclodextrin. The adsorbent provides a molecular-level dispersion of Cu(I), which is particularly beneficial to the adsorptive removal of aromatic sulfur thiophene, and is impossible to be realized through the conventional thermal method.

An unprecedented guest–host redox strategy is developed to generate strong basicity on mesoporous silica, which breaks the tradition of thermally induced decomposition of precursors. New materials possessing ordered mesostructure, strong basicity, and excellent catalytic activity are thus successfully fabricated at a low temperature.