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"Hydrocracking"
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High-efficiency Ce-modified ZSM-5 nanosheets for waste plastic upgrading
Zeolite-based catalyst hydrocracking of plastics is a potential strategy for mitigating the environmental impacts of plastic wastes and recycling valuable resources, but difficult mass transfer, low concentration of acid sites, and high cost are still barriers to their practical applications. In this paper, we report an excellent hydrocracking catalyst of ZSM-5 nanosheets (Ce/b-ZSM-5) modified by Ce species with high conversion up to 96.3%, C
3
–C
5
selectivity up to 80.9%, and good stability during the hydrogenation of low-density polyethylene. Through comprehensive studies, b-ZSM-5 shows higher molecular diffusion efficiency and acid site concentrations compared with normal ZSM-5 (n-ZSM-5) and hollow ZSM-5 (h-ZSM-5). The introduction of Ce species into b-ZSM-5 further increases the density of Brønsted (B) and Lewis (L) acid sites as active sites, which enhances the adsorption of substrates and facilitates the formation of intermediates and desorption of products. As a result, the hydrocracking activity of Ce/b-ZSM-5 is significantly improved.
Journal Article
Mechanistic classification and benchmarking of polyolefin depolymerization over silica-alumina-based catalysts
Carbon-carbon bond cleavage mechanisms play a key role in the selective deconstruction of alkanes and polyolefins. Here, we show that the product distribution, which encompasses carbon range and formation of unsaturated and isomerization products, serves as a distinctive feature that allows the reaction pathways of different catalysts to be classified. Co, Ni, or Ru nanoparticles immobilized on amorphous silica-alumina, Zeo-Y and ZSM-5, were evaluated as catalysts in the deconstruction of
n
-hexadecane model substrate with hydrogen to delineate between different mechanisms, i.e., monofunctional- (acid site dominated) or bifunctional-hydrocracking (acid site & metal site) versus hydrogenolysis (metal site dominated), established from the product distributions. The ZSM-5-based catalysts were further studied in the depolymerization of polyethylene. Based on these studies, the catalysts are plotted on an activity-mechanism map that functions as an expandable basis to benchmark catalytic activity and to identify optimal catalysts that afford specific product distributions. The systematic approach reported here should facilitate the acceleration of catalyst discovery for polyolefin depolymerization.
Product distributions have been used to classify the depolymerization pathways of polyolefins catalyzed by silica-alumina-based catalysts to construct an activity-mechanism map as a benchmarking tool to facilitate catalyst discovery.
Journal Article
Upcycling polyolefins to methane-free liquid fuel by a Ru1-ZrO2 catalyst
Upcycling waste plastics into liquid fuels presents significant potential for advancing the circular economy but is hindered by poor selectivity and low-value methane byproduct formation. In this work, we report that atomic Ru-doped ZrO
2
can selectively convert 100 grams of post-consumer polyethylene and polypropylene, yielding 85 mL of liquid in a solvent-free hydrocracking. The liquid (C
5
-C
20
) comprises ~70% jet-fuel-ranged branched hydrocarbons (C
8
-C
16
), while the gas product is liquefied-petroleum-gas (C
3
-C
6
) without methane and ethane. We found that the atomic Ru dopant in the Ru-O-Zr moiety functionalizes its neighboring O atom, originally inert, to create a Brønsted acid site. This Brønsted acid site, rather than the atomic Ru dopant itself, selectively governs the internal C−C bond cleavage in polyolefins through a carbonium ion mechanism, thereby enhancing the yield of jet-fuel-ranged hydrocarbons and suppressing methane formation. This oxide modulation strategy provides a paradigm shift in catalyst design for hydrocracking waste plastics and holds potential for a broad spectrum of applications.
Converting waste plastics into liquid fuels holds great promise for advancing the circular economy but is challenged by poor selectivity and unwanted methane byproduct formation. Here, the authors present a Ru
1
-ZrO
2
catalyst that efficiently upcycles plastic waste into high-value jet fuel–range hydrocarbons with minimal methane production.
Journal Article
Unraveling the role of water in mechanism changes for economically viable catalytic plastic upcycling
The surge in global plastic production, reaching 400.3 million tons in 2022, has exacerbated environmental pollution, with only 11% of plastic being recycled. Catalytic recycling, particularly through hydrogenolysis and hydrocracking, offers a promising avenue for upcycling polyolefin plastic, comprising 55% of global plastic waste. This study investigates the influence of water on polyolefin depolymerization using Ru catalysts, revealing a promotional effect only when both metal and acid sites, particularly Brønsted acid site, are present. Findings highlight the impact of Ru content, metal-acid balance, and their proximity on this interaction, as well as their role in modulating the isomerization process, affecting product selectivity. Additionally, the interaction facilitates the suppression of coke formation, ultimately enhancing catalyst stability. A comprehensive techno-economic and life cycle assessment underscores the viability and environmental benefits of the process, particularly in the presence of water. These insights advance understanding and offer strategies for optimizing polyolefin plastic recycling processes.
Catalytic hydrogenolysis and hydrocracking present a promising approach for upcycling polyolefin plastics. Here, the authors highlight the role of water in catalytic plastic upcycling, emphasizing that catalysts with an optimal metal-acid balance significantly improve polyethylene depolymerization when water is present.
Journal Article
The Role of Copper in Bimetallic Nickel–Copper BEA Zeolite Catalysts and Their Activity in the Hydrocracking Process of Rapeseed Oil
The main goal of this work was to determine the role of copper in bimetallic nickel–copper BEA zeolite catalysts prepared by sequential impregnation and co-impregnation, as well as defining the influence of the method of impregnation on the catalytic activity of the described catalysts. The all-prepared samples were tested in hydrocracking reactions with rapeseed oil as a feedstock. The physicochemical properties of the catalytic materials were determined using H2-TPR, TPD-NH3, XRD, BET, and SEM-EDS techniques. The reaction products were analyzed using chromatographic techniques (HPLC and GC-MS). The bimetallic systems obtained post-impregnation exhibited lower conversions of rapeseed oil than catalysts synthesized by co-impregnation. For all bimetallic catalysts, oil conversion was higher than for the monometallic copper BEA zeolite catalyst. This indicates that nickel is responsible for better oil conversion. The highest oil conversion (92.7%) was noted for the co-impregnated 5%Ni-5%Cu_BEA zeolite catalyst. For all tested catalysts, the highest selectivity was noted for the gasoil fraction. However, the presence of copper in bimetallic Cu-Ni_BEA zeolite catalysts led to increased selectivity towards gasoline and kerosene compared to the monometallic nickel BEA zeolite catalyst.
Journal Article
Carbon–carbon bond cleavage for a lignin refinery
Carbon–carbon bonds, ubiquitous in lignin, limit monomer yields from current depolymerization strategies, which mainly target C–O bonds. Selective cleavage of the inherently inert σ-type C–C bonds without pre-functionalization remains challenging. Here we report the breaking of C–C bonds in lignin obtained upon initial disruption of labile C–O bonds, achieving monocyclic hydrocarbon yields up to an order of magnitude higher than previously reported. The use of a Pt (de)hydrogenation function leads to olefinic groups close to recalcitrant C–C bonds, which can undergo β-scission over zeolitic Brønsted acid sites. After confirming that this approach can selectively cleave common C–C linkages (5–5′, β–1′, β–5′ and β–β′) in lignin skeletons, we demonstrate its utility in the valorization of various representative lignins. A techno-economic analysis shows the promise of our method for producing gasoline- and jet-range cycloalkanes and aromatics, while a life-cycle assessment confirms its potential for CO2-neutral fuel production.Carbon–carbon bonds are ubiquitous in lignin, limiting monomer yields from current depolymerization strategies mainly targeting C–O bonds. Now, a bifunctional hydrocracking approach uses a Pt/zeolite catalyst to break C–C bonds in lignin waste, achieving monocyclic hydrocarbon yields up to 54 C%.
Journal Article
Engineering Hierarchical NiMo/USY Catalysts for Selective Hydrocracking of Naphthalene to BTX
The selective hydrocracking of polycyclic aromatic hydrocarbons to BTX requires precise control over catalyst porosity and metal–acid balance. Hierarchical porosity, integrating microporous and mesoporous networks, is pivotal for enhancing mass transport and regulating reaction pathways. USY zeolites were engineered to create distinct hierarchical architectures via HCl, urea, and NaOH–surfactant treatments. HCl treatment constructed a gradient pore acidity system, urea treatment enhanced acidity while preserving microporosity, and NaOH–surfactant fabricated ordered mesopores with reduced acidity. The catalyst with the HCl-engineered gradient pore (NiMo/YH-1) achieved a 91% BTX yield at 425 °C in naphthalene hydrocracking, outperforming others. This performance is attributed to its gradient structure that enforces an optimal “hydrogenation-then-cracking” pathway, highlighting the critical role of tailored hierarchical porosity.
Journal Article
Roles of Catalysts and Feedstock in Optimizing the Performance of Heavy Fraction Conversion Processes: Fluid Catalytic Cracking and Ebullated Bed Vacuum Residue Hydrocracking
Petroleum refining has been, is still, and is expected to remain in the next decades the main source of energy required to drive transport for mankind. The demand for automotive and aviation fuels has urged refiners to search for ways to extract more light oil products per barrel of crude oil. The heavy oil conversion processes of ebullated bed vacuum residue hydrocracking (EBVRHC) and fluid catalytic cracking (FCC) can assist refiners in their aim to produce more transportation fuels and feeds for petrochemistry from a ton of petroleum. However, a good understanding of the roles of feed quality and catalyst characteristics is needed to optimize the performance of both heavy oil conversion processes. Three knowledge discovery database techniques—intercriteria and regression analyses, and artificial neural networks—were used to evaluate the performance of commercial FCC and EBVRHC in processing 19 different heavy oils. Seven diverse FCC catalysts were assessed using a cascade and parallel fresh catalyst addition system in an EBVRHC unit. It was found that the vacuum residue conversion in the EBVRHC depended on feed reactivity, which, calculated on the basis of pilot plant tests, varied by 16.4%; the content of vacuum residue (VR) in the mixed EBVRHC unit feed (each 10% fluctuation in VR content leads to an alteration in VR conversion of 1.6%); the reaction temperature (a 1 °C deviation in reaction temperature is associated with a 0.8% shift in VR conversion); and the liquid hourly space velocity (0.01 h-1 change of LHSV leads to 0.85% conversion alteration). The vacuum gas oil conversion in the FCC unit was determined to correlate with feed crackability, which, calculated on the basis of pilot plant tests, varied by 8.2%, and the catalyst ΔCoke (each 0.03% ΔCoke increase reduces FCC conversion by 1%), which was unveiled to depend on FCC feed density and equilibrium FCC micro-activity. The developed correlations can be used to optimize the performance of FCC and EBVRHC units by selecting the appropriate feed slate and catalyst.
Journal Article