Wenming Hao

The catalytic performance of a range of USY zeolites on the hydrocracking of 9,10-dihydrophenanthrene (9,10-DHP) at relatively low temperatures in an autoclave was investigated. During the initial phase of the 9,10-DHP hydrocracking, hydrogenation/dehydrogenation and hydrogen transfer reactions are in competition with the central ring opening (CRO) reaction. As the temperature rises, the CRO reaction is favored, while the hydrogenation/dehydrogenation reactions diminish. The catalyst's behavior varies significantly between the low and high density ranges of Brønsted acid sites (BAS). When the BAS density is below 179 μmol/g, the selectivity towards tetrahydrophenanthrene and CRO products (biphenyls) remains consistent under identical reaction conditions. When the BAS density exceeds this range, the selectivity for tetrahydrophenanthrene declines, and the selectivity for CRO products notably increases with the density of BAS. Pore blockage in USY zeolites due to coke deposition is more sensitive to BAS in the low acid density range compared to the high range.

The addition of an anionic surfactant AESA in zeolite synthesis resulted in zeolite Beta with improved crystallinity and crystal completeness, increased framework Si/Al ratio, increased yield and enrichment of polymorph-A.

To reveal the influence of acid sites with different spatial locations of USY zeolite with different micro-/mesoporous structures and Si/Al ratio, catalytic cracking of methylcyclohexane on the zeolites is employed to study the synergism effects of acid sites and porous structures (“active region”) in the hierarchical USY zeolites. The results showed that the hierarchical USY zeolites have increased numbers of accessibly strong Brønsted acid sites and greatly enhanced diffusion ability due to the hierarchical pore-structure, resulting in mainly monomolecular protolytic scission in cracking reactions and less bimolecular hydrogen transfer. The isomerization reaction is from intramolecular transalkylation and the isomerics are the intermediates of the cracking reaction. The protolytic cracking that occurs in hierarchical high-silica USY-zeolites follows the Haag-Dessau cracking.

Cetyltrimethylammonium bromide (CTAB) has been successfully used as mesoporogen in the single or dual templating system of hierarchical zeolite Beta synthesis. However, the mechanism of the formation of the pore structure of hierarchical zeolite Beta still remains elusive. In this work, we investigated the formation mechanism of hierarchical zeolite Beta focusing on the role of CTAB in a dual templating system. It is found that the induction period was prolonged by the presence of CTAB during the crystallization process, as evidenced by the characterization of XRD and IR. The change of the surface tension of the supernatant in the hierarchical zeolite Beta synthesis solution and the change of weight loss of the template-included hierarchical zeolite Beta in the TG curve after different crystallization time evidenced that CTAB was involved in the synthesis and incorporated within the solid phase at the first stage when mesopores were formed, which was released later into the solution when the crystallized microporous structure was developed. N 2 adsorption and desorption results also confirmed the formation of ordered mesopores with narrow pore size distribution at the first stage, which became wider with longer crystallization time. The DTG results of the hierarchical zeolite Beta with different starting Si/Al ratio and different CTAB concentrations in the synthesis solution revealed that CTA + worked both as structure directing agent (SDA) for micropores and mesoporogen for the secondary lager pores in the matrix of hierarchical zeolite Beta. When the template included hierarchical zeolite Beta was treated in ethanol, the CTA + cations working as the micropore SDA could not be dissolved in ethanol, while those working as the mesoporogen could be dissolved in ethanol. Moreover, CTA + competed with TEA + to work as the SDA for micropores, with a decrease of the total amount of CTA + and TEA + when the concentration of CTAB in the synthesis solution was increased. It is anticipated that the understanding of the role of CTAB in the formation of hierarchical zeolite Beta can provide a basis for designing the synthesis of hierarchical zeolites.

The adsorption of toluene and 1,3,5-trimethylbenzene and the catalytic transformation of 1,3,5-trimethylbenzene are applied as probing approaches to characterize the pore system of hierarchical EU-1 zeolites prepared using organofunctionalized fumed silica as the silicon source. The adsorption and diffusion of toluene and 1,3,5-trimethylbenzene are significantly improved in the hierarchical EU-1 zeolites compared with the conventional microporous EU-1 zeolite. The adsorption kinetics of toluene and 1,3,5-trimethylbenzene suggested that introducing mesopores significantly increases the rate of adsorption and improved the diffusion of large molecules. In the catalytic transformation of 1,3,5-trimethylbenzene, the conversion of 1,3,5-trimethylbenzene on the hierarchical EU-1 zeolites is doubled compared with the conventional microporous EU-1 zeolite, due to the improved diffusion of bulky molecules and enhanced accessibility of active sites in the hierarchical EU-1 structure. Although isomerization is the main reaction, differences are observed in the product ratios of isomerization to disproportionation between the hierarchical EU-1 zeolites and the microporous counterpart with different times on stream. The transformation of 1,3,5-trimethylbenzene over the hierarchical EU-1 zeolites has a higher isomerization to disproportionation ratio than that over the microporous EU-1 zeolite; this is due to the increased mesoporosity.

The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (β-SiC) but also significant amounts of the 2H or the 6H polytypes (α-SiC) in the SiC.

CO is a toxic gas discharged as a byproduct in tail gases from different industrial flue gases, which needs to be taken care of urgently. In this study, a CuCl/AC adsorbent was made by a facile route of physically mixing CuCl₂ and Cu(HCOO)₂ powder with activated carbon (AC), followed by heating at 533 K under vacuum. The samples were characterized by X-ray powder diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), N₂ adsorption/desorption, and scanning electron microscopy (SEM). It was shown that Cu(II) can be completely reduced to Cu(I), and the monolayer dispersion threshold of CuCl on AC support is 4 mmol·g⁻¹ AC. The adsorption isotherms of CO, CO₂, CH₄, and N₂ on CuCl/AC adsorbents were measured by the volumetric method, and the CO/CO₂, CO/CH₄, and CO/N₂ selectivities of the adsorbents were predicted using ideal adsorbed solution theory (IAST). The obtained adsorbent displayed a high CO adsorption capacity, high CO/N₂, CO/CH₄, and CO/CO₂ selectivities, excellent ad/desorption cycle performance, rapid adsorption rate, and appropriate isosteric heat of adsorption, which made it a promising adsorbent for CO separation and purification.