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Amorphous aluminosilicate nanosheets (a-ASns) consisting of small homogeneous nanoplates were synthesized in a bottom-up approach using the “hydrophilic two-dimensional reactor in amphiphilic phases” (TRAP) method. We found the appropriate operation variable to control the composition of a-ASns: the concentration of base catalysts.Graphical Abstract

Catalyst deactivation owing to carbon deposition on Ni-based catalysts is a serious problem in reactions involving hydrocarbon compounds. In particular, the catalytic decomposition of methane (CDM), which produces hydrogen and carbon, cannot prevent carbon deposition on the catalysts. Because the formation of carbon-coated Ni particles leads to a decrease in activity, it is necessary to generate carbon nanotubes tipped with Ni particles. Herein, this work reports Cr and Ni catalysts supported by dealuminated beta zeolites. Cr and Ni loaded on dealuminated beta zeolites showed remarkably higher CDM activity and longer catalyst lifetime than only Ni loaded on dealuminated beta zeolites. The optimal loading amounts of Ni and Cr were 50 and 1 wt %, respectively. The maximum H2yield over the optimal Cr and Ni loaded on dealuminated beta zeolite was 22.5%, while that over only Ni (50 wt %) loaded on dealuminated beta zeolite was 16.5%. The state of the metal species was investigated using hydrogen temperature-programmed reduction measurements and determined the optimum reduction conditions. In addition, the deposited carbon was evaluated by using thermogravimetric analysis, transmission electron microscopy, and Raman spectroscopy. Cr3+species enhance catalytic activity and contribute to the formation of highly crystalline carbon nanotubes.

The catalytic conversion of ethylene to propylene (ETP) has been proposed as a novel and attractive process to meet the increasing demand for propylene. Several ETP catalysts have been studied and developed, and catalysts based on Ni are viewed as promising options due to their cost-effectiveness and high levels of activity. Nevertheless, catalysts based on Ni are prone to deterioration due to the aggregation of Ni particles and the generation of carbon nanotubes (CNT) during the ETP process. As a solution to these drawbacks, we synthesized a Ni-encapsulated core–shell-structured zeolite catalyst by overgrowth of silicalite-1 shell layers on Ni-loaded ZSM-5. The silicalite-1 shell layers inhibited the aggregation of Ni nanoparticles and the formation of CNT, leading to an improved catalytic performance. The best sample among the synthesized catalysts exhibited a maximum propylene yield of 28.3 C-mol % and butene yield of 17.8 C-mol % in the ETP reaction test. The maximum combined propylene and butene selectivity was 69.2%. To support the above result, transmission electron microscopy observation of the spent catalysts revealed that the core–shell structure prevented Ni aggregation and the formation of CNT. In addition, the reduction in the amount of coke deposition (mainly CNT) for the core–shell catalyst after the reaction was measured by TG analysis. For the spent catalyst without the silicalite-1 shell layers, the coke weight in the catalyst weight was 1.7%, whereas it was 0.7% for the catalyst with the silicalite-1 shell layers. Furthermore, reaction tests with different contact times verified the roles of the acidic sites of the ZSM-5 support and Ni species in the ETP reaction, and the reaction pathway was also identified.