Yuan Chun

One‐Pot Synthesis of Potassium‐Functionalized Mesoporous γ‐Alumina: A Solid Superbase

The synthesis of mesoporous superbases is a challenge for chemists owing to their wide range of potential applications in green chemistry and the difficulties inherent in their preparation. Mesoporous superbasic materials are extremely desirable for use in environmentally benign and economical chemical processes as they can catalyze diverse reactions under mild conditions, therefore many attempts have been made to prepare mesoporous solid bases, for example, by incorporating nitrogen-containing species into mesoporous silica and by grafting organic bases onto mesoporous silica. Owing to the reaction of these strongly basic species with silica, however, most of the solid bases reported to date are relatively weak, which suggests that it is difficult to generate superbasicity on mesoporous silica. In contrast to silica, alumina, especially that of the g-type, is a well-known support for a variety of solid strong bases, which means that the occurrence of mesoporous aluminas affords a good opportunity to prepare mesoporous superbasic materials. Unfortunately, the stability of mesoporous aluminas is relatively poor and structural damage occurs to a greater or lesser extent even if postsynthesis modification is performed carefully. This drawback hinders the application of mesoporous aluminas in preparing solid superbases and other functional materials. Herein we report a new strategy for the one-pot synthesis of potassium-functionalized mesoporous g-alumina that involves the use of K2CO3 to adjust the pH value of the reaction system such that the base precursor KNO3 is produced in situ by hydrolysis of Al(NO3)3. KNO3 is decomposed to the strongly basic species K2O on the g-Al2O3 that is also formed in situ during the same calcination process. This strategy allows the synthesis and modification of mesoporous alumina in a one-pot process, avoids post-treatment framework damage, and saves time and energy. The basic materials obtained exhibit a well-defined mesoporous structure and superbasicity and are active in 1-hexene isomerization, which means that they are valuable candidates for selective adsorption and catalysis involving strong solid bases. The synthetic process is shown schematically in Figure S1 in the Supporting Information. KNO3-coated mesoporous boehmite (AlOOH) with a K/Al atomic ratio (n) of between 0 and 0.27 (Table 1) is obtained initially (denoted as MA-B (n=

New Attempt at Directly Generating Superbasicity on Mesoporous Silica SBA-15

Direct generation of superbasicity on mesoporous silica SBA-15 was realized by tailoring the host-guest interaction, and calcium species were selected as the guest in modifying SBA-15. The results show that calcium species could be homogeneously distributed on the surface of SBA-15. Because of the host-guest interaction, the decomposition of the supported calcium nitrate was apparently easier than the bulk one. Surprisingly, the calcium nitrates modified SBA-15 (CaNS) samples exhibited superbasicity with good preservation of the mesostructure after activation, differing from the potassium nitrate loaded SBA-15 samples that displayed weak basicity with collapsed mesostructure. The present superbasic CaNS materials also possess good water resistance and high surface areas, up to 429 m(2) g(-1), which is promising for their potential applications in adsorption and catalysis. Further investigation concerning the roles played by the guest in basicity formation on SBA-15 was conducted. The samples modified by Group 2 metal nitrates showed strong basicity with base strength (H-) of 22.5-27.0 and good preservation of mesostructure. In contrast, loading Group 1 metal nitrates on SBA-15 produced samples with weak basicity ( H-=9.3-15.0) and collapsed mesostructure after activation. Such differences can be related to the interaction between the resulting metal oxide and the silica support, as well as the mobility of the cations in the metal oxide.

Dispersion of potassium nitrate and the resulting basicity on alumina and zeolite NaY

Dispersion and decomposition of KNO3 on γ-alumina and NaY zeolite as well as Al2O3-NaY porous material were examined, and the basicity of these resulting solid bases were characterized. KNO3 was highly dispersed on zeolite NaY and AlPO4-5 but difficult to decompose, due to the lack of octahedral vacant sites in the zeolite provided for the insertion of K+ cations. If the amount of KNO3 loaded was below the monolayer dispersion threshold, it could be well dispersed and provoked a basic strength (H-) of 18.4 on the alumina. When the amount of KNO3 was above the threshold on the alumina, it only dispersed and decomposed during evacuation at 873 K but generated some unusually strong basic sites with strength (H-) of 27.0 on γ-alumina.

Directly transforming as-synthesized MCM-41 to mesoporous MFI zeolite

Mesoporous MFI zeolite is fabricated through impregnating a structure-directing agent into as-synthesized MCM-41 followed by dry-gel conversion to transform amorphous silica to zeolite crystal. The original surfactant in the as-synthesized MCM-41 is used as the necessary mesoporogen to direct the mesopore genesis of zeolites, using the process of streaming to spur the transformation and tailoring the texture of mesoporous ZSM-5 by adjusting the Si : Al ratio in the MCM-41 source. The resulting sample is characterized by X-ray diffraction, IR spectroscopy, TEM and N2 adsorption to evaluate the textural properties of the mesoporous zeolite. Two kinds of nitrosamines with different structures are used as probe molecules to survey the adsorption function of the resulting mesoporous zeolite. Mesoporous zeolites exhibit good adsorption capacities and exceed either microporous zeolite or mesoporous silica. This synthesis strategy omits the fabrication and removal of the carbon template and simplifies the synthesis process of mesoporous zeolites, saving energy and time.

Solvent-free surface functionalized SBA-15 as a versatile trap of nitrosamines

Dispersion of copper oxide via a solvent-free method enables mesoporous silica SBA-15 to become a versatile trap of nitrosamines, exhibiting a high capability to capture volatile nitrosamines and tobacco special nitrosamines (TSNA). 3%CuO/SBA-15 can remove 85% of N-nitrosopyrrolidine (NPYR) in gaseous flow, one fifth more than that by the analogous via one-pot method, while 5%CuO/SBA-15 traps all N-nitrosonornicotine (NNN) in solution with a concentration of 0.6 mmol l−1, superior to NaY zeolite. The dispersion of the copper guest in SBA-15 is assessed by XRD, H2-TPR, NO2-TPD and UV-Vis methods.

Basic catalytic behavior of MgO directly dispersed on zeolites by microwave irradiation

Abstract MgO could be directly dispersed onto zeolites-L, ZSM-5, β and AlPO 4 -11 and hexagonal mesoporous silica (HMS) molecular sieve by microwave irradiation. New solid bases were formed being active in the dehydrogenation of isopropanol or the isomerization of cis -2-butene.

Superbase derived from zirconia-supported potassium nitrate

Superbasic sites can be generated on ZrO2 by loading with KNO3. The spontaneous dispersion capacity of KNO3 on ZrO2 was 8.1 K+ nm−2 and the KNO3 starts to decompose near 350°C, much lower than that for the decomposition of unsupported KNO3. KNO3/ZrO2 samples exhibited a high activity in both dehydrogenation of isopropanol at 400°C and isomerization of cis-but-2-ene at 0°C. Moreover, they possessed the base strength of H−=26.5, which is the characteristic of solid superbase.

An investigation of KF modification to generate strong basic sites on NaY zeolite

Abstract Through an interaction with zeolite NaY to liberate KOH, KF modification provoked a basicity similar to that of KOH/NaY, and the resulting catalyst exhibited the same basic catalytic properties as KOH/NaY in the decomposition of isopropanol (IPA). Owing to the competitive reaction of the silicon component in NaY with the KOH liberated to form species with a low base strength, however, KF modification did not generate strong basic sites on NaY. Coating alumina onto NaY by hydrolysis of aluminum isopropoxide produced a new porous material without any significant change in the pore size of the NaY zeolite, and after modification with KF this new solid base exhibited a higher base strength (H−=17.2) than the parent NaY zeolite (H−=9.3).

New unusually strong solid basic material derived from KL zeolite impregnated with KNO3

Abstract Dispersion and decomposition of KNO 3 on KL zeolite can create strong basic sites upon calcination at 600 °C, and their basic strength can reach H − = 27.0 which is the characteristic of a solid superbase. The resulting catalyst showed a high catalytic activity for the isomerization of cis -but-2-ene at 0 °C.

MgO/KL : strong basic zeolite prepared by microwave radiation

MgO can be directly dispersed on KL zeolite by microwave radiation and forms strong basic sites with strength of H−=18.4. The resulting strong basic zeolite exhibits a high activity in cis-2-butene isomerization at 0°C.