Ethylene Conversion into Propylene and Aromatics on HZSM-5: Insights on Reaction Routes and Water Influence

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Zeolite chemistry and catalysis are expected to play a decisive role in the next decade(s) to build a more decentralized renewable feedstock-dependent sustainable society owing to the increased scrutiny over carbon emissions. Therefore, the lack of fundamental and mechanistic understanding of these processes is a critical "technical bottleneck" that must be eliminated to maximize economic value and minimize waste. We have identified, considering this objective, that the chemistry related to the first-generation reaction intermediates (i.e., carbocations, radicals, carbenes, ketenes, and carbanions) in zeolite chemistry and catalysis is highly underdeveloped or undervalued compared to other catalysis streams (e.g., homogeneous catalysis). This limitation can often be attributed to the technological restrictions to detect such "short-lived and highly reactive" intermediates at the interface (gas-solid/solid-liquid); however, the recent rise of sophisticated spectroscopic/analytical techniques (including under in situ/operando conditions) and modern data analysis methods collectively compete to unravel the impact of these organic intermediates. This comprehensive review summarizes the state-of-the-art first-generation organic reaction intermediates in zeolite chemistry and catalysis and evaluates their existing challenges and future prospects, to contribute significantly to the "circular carbon economy" initiatives.

Biochar-advanced thermocatalytic salvaging of the waste disposable mask with the production of hydrogen and mono-aromatic hydrocarbons

The salvaging of the waste disposable mask was conducted in this study through catalytic pyrolysis over corn stover derived biochar catalyst combined with the boosted generation of hydrogen and mono-aromatic hydrocarbons for the first time. In the absence of biochar, up to 53 wt% of wax was observed at 550 ºC, whereas at the biochar/mask ratio of 2, around 41 wt% of liquid oil was produced without the formation of wax. The hydrogen content in the gas stream was about 26 vol% at 600 ºC for non-catalytic pyrolysis, which increased to around 55 vol% at the expense of light hydrocarbons such as methane and C_2-4 for the catalytic process with the biochar/mask ratio of 3. In resulting liquid oil, the content of mono-aromatics, especially toluene, xylenes, and ethylbenzene was about 55% for catalytic runs, which was far greater than that of 38% from the non-catalytic run. Interestingly, the dyes released from mask pyrolysis could be completely captured/adsorbed by biochar, leading to a much cleaner oil. After 10 cycles of reuse at 600 ºC without regeneration, the biochar still held a good selectivity toward hydrogen and mono-aromatic hydrocarbons. This study exemplified a readily accessible concept and pathway of 'waste against waste' targeted to upcycle waste disposable masks over biochar from biomass waste.

Towards the development of the emerging process of CO2 heterogenous hydrogenation into high-value unsaturated heavy hydrocarbons

The emerging process of CO₂ hydrogenation through heterogenous catalysis into important bulk chemicals provides an alternative strategy for sustainable and low-cost production of valuable chemicals, and brings an important chance for mitigating CO₂ emissions. Direct synthesis of the family of unsaturated heavy hydrocarbons such as α-olefins and aromatics via CO₂ hydrogenation is more attractive and challenging than the production of short-chain products to modern society, suffering from the difficult control between C-O activation and C-C coupling towards long-chain hydrocarbons. In the past several years, rapid progress has been achieved in the development of efficient catalysts for the process and understanding of their catalytic mechanisms. In this review, we provide a comprehensive, authoritative and critical overview of the substantial progress in the synthesis of α-olefins and aromatics from CO₂ hydrogenation via direct and indirect routes. The rational fabrication and design of catalysts, proximity effects of multi-active sites, stability and deactivation of catalysts, reaction mechanisms and reactor design are systematically discussed. Finally, current challenges and potential applications in the development of advanced catalysts, as well as opportunities of next-generation CO₂ hydrogenation techniques for carbon neutrality in future are proposed.

Catalytic upcycling of waste plastics over nanocellulose derived biochar catalyst for the coupling harvest of hydrogen and liquid fuels

A powerful simple biochar catalyst derived from nanocellulose was applied to the catalytic upcycling of waste plastics into H₂ and liquid fuels for the first time. For the results from model low-density polyethylene (LDPE) pyrolysis, the C₈-C₁₆ aliphatics and monocyclic aromatics were dominant constitutes of the liquid product with the yields ranging from 22 to 68 wt%. At the temperature of 500 °C and biochar to LDPE ratio surpassing 3, the LDPE could be completely degraded into liquid and gas without wax production. A wax yield of 16 wt% was observed at the temperature of 450 °C and biochar to LDPE ratio of 4, which was dramatically lower than that (77 wt%) from the absence of biochar at the temperature of 500 °C. Up to 92 vol% of H₂ was detected in the gaseous product with a yield of 36 wt%. The lower temperatures and higher biochar to LDPE ratios favored increasing the generation of H₂ at the expense of light gas C_nH_m especially CH₄. Moreover, this biochar catalyst was tested effectively to convert the real waste plastics including grocery bags and packaging tray into valuable liquid and H₂-enriched gas.