Search

Nickel-supported CHA-type zeolites with different framework compositions including borosilicate, gallosilicate and aluminosilicate were synthesized. The effect of heteroatoms in the framework on th...

AEI-type aluminosilicate zeolites with sheet-like morphology were successfully synthesized by the crystal growth inhibitor (CGI)-assisted method, where cetyltrimethylammonium bromide (CTAB) worked as a CGI. The obtained sheet-like AEI-type aluminosilicates showed a higher yield of butenes and longer catalytic lifetime in the direct conversion of propene to butenes than the conventional sample. The improvement of catalytic performance originated from tuning the molecular diffusion in the zeolite particles. The sheet-like morphology gave a higher molecular diffusivity, and consecutive reactions were suppressed. Moreover, there was a significant difference in the product distribution of butene isomers; linear butenes and iso-butene were the dominant product over the typical AEI-type aluminosilicate with cubic particles induced by the shape selectivity into zeolitic micropores, while the sheet-like one yielded a higher selectivity for iso-butene. It was revealed that the distribution of Bronsted acid sites between internal and external surfaces could be controlled by increasing the external surface area coming from the sheet-like particles.

The development of simple catalysts with high performance in the selective oxidation of methane to syngas at low temperature has attracted much attention. Here we report a nickel-based solid catalyst for the oxidation of methane, synthesised by a facile impregnation method. Highly dispersed ultra-small NiO particles of 1.6 nm in size are successfully formed on the MOR-type zeolite. The zeolite–supported nickel catalyst gives continuously 97–98% methane conversion, 91–92% of CO yield with a H2/CO ratio of 2.0, and high durability without serious carbon deposition onto the catalyst at 973 K. DFT calculations demonstrate the effect of NiO particle size on the C-H dissociation process of CH4. A decrease in the NiO particle size enhances the production of oxygen originating from the NiO nanoparticles, which contributes to the oxidation of methane under a reductive environment, effectively producing syngas. Catalytic oxidation of methane to syngas is an important process, but efficient and stable catalyts remain in demand. Here dispersion of nickel on zeolites yields nickel oxide nanoparticles as small as 1.6 nm which act as selective and efficient catalysts for conversion of methane to syngas.

Incorporation of B atoms into the AEI-type framework was successfully achieved by addition of boric acid into the starting gel. The gel compositions, the Si/Al and Si/B ratio, and the calcination conditions were extensively investigated to tune acidic properties of the AEI-type zeolite. The incorporation of B into the framework was confirmed by solid state NMR and FT-IR techniques. In-situ FT-IR spectroscopy using CO as a probe molecule was applied to the evaluation of the acidic property. As the result of in-situ FT-IR measurement, thus obtained AEI-type boroaluminosilicate zeolites showed weak acidic properties derived from framework B species compared to the aluminosilicate one. Finally, the catalytic properties of the synthesized AEI-type zeolites in the ethene conversion reaction were investigated. We found that the AEI-type boroaluminosilicate catalyst showed a long catalytic life and a high selectivity to butenes.

A series of MCM-68 zeolites with different Si/Al ratios were prepared by treatment with nitric acid and compared with beta zeolites. Speciation of aluminum and location of acid sites changed depending on the Si/Al ratio. The location of Bronsted acid sites in MCM-68 samples was able to be classified by FT-IR measurements with pyridine and 2,6-di-tert-butylpyridine as probe molecules, and the number of Bronsted acid sites was quantified according to the locations. For high-aluminum MCM-68, Bronsted acid sites were broadly distributed in both the 12-ring channel and 10-ring windows as well as inside the supercage. The Bronsted acid sites in the 12-ring channel were easily removed by the acid treatment, and consequently, high-silica MCM-68 had Bronsted acid sites predominantly in the 10-ring windows and inside the supercage. 27Al MQMAS NMR spectra of high-silica MCM-68 showed two specific peaks assignable to T6 and T7 sites, which did not face the 12-ring channel, forming the Bronsted acid sites highly toler...

Titanated chabazites (Ti–CHAs) with various Si/Al and Si/Ti ratios were prepared from titanated faujasite (Ti–FAU) by optimizing the NaOH/SiO 2 and H 2 O/SiO 2 ratios in the starting reaction mixtures. The peak assigned to isolated tetrahedrally coordinated Ti species was clearly observed at ∼220 nm in the UV–vis spectra and at ∼960 cm −1 in the FT-IR spectra of the Ti–CHA, confirming that Ti was incorporated in the zeolite framework. The thermal stability of the Ti–CHAs was higher than that of non-modified CHAs synthesized from FAU or amorphous aluminosilicate hydrogels. The framework structure of Ti–CHAs with Si/Ti ratios of 33 and 64 was unchanged even after calcination at 1000 °C for 1 h, indicating the enhanced thermal stability by Ti modification. We also prepared Cu-loaded zeolite catalysts using Ti–CHA and non-modified CHA and investigated their catalytic performance for the selective catalytic reduction of NO x by ammonia. Although there was no difference between the NO conversion on the two fresh catalysts, the NO conversion on the Cu-loaded Ti–CHA catalyst after hydrothermal treatment at 900 °C for 4 h was considerably higher than that on the Cu-loaded CHA catalyst, indicating the higher hydrothermal stability of Cu-loaded Ti–CHA catalyst.

The isomorphous substitution of zeolite framework is a useful means of improving the catalytic performance of zeolites. Such materials are also known to sometimes show catalytic behaviors that typical aluminosilicate zeolites do not exhibit. In the work reported herein, a two-step synthesis method comprising mechanochemical and hydrothermal treatments was used to synthesize Ga-substituted MFI-type zeolites ([Ga]-MFI) with various Si/Ga ratios. The initial planetary ball milling of SiO2 and β-Ga2O3 was central to this synthetic method as it induced mechanochemical reaction between these oxides, which resulted in the formation of amorphous composite containing Si–O–Ga linkages. A subsequent hydrothermal synthesis employing this composite as a source of both Si and Ga gave MFI zeolites incorporating tetrahedral Ga species in their frameworks. A [Ga]-MFI synthesized in this manner with a Si/Ga ratio of 50 selectively transformed methane into CO in the presence of oxygen. In contrast, [Ga]-MFI prepared viaa conventional one-pot hydrothermal synthesis accelerated the complete oxidation to produce CO2.