Service Life Of Catalyst Research Articles

Novel methodology for targeting the optimal reactor and operating parameters based on the chemical system’s overall performance within catalyst lifecycle

Catalyst deactivation affects chemical system performance and reactor operation. A systematic method is proposed for targeting the optimal reactor, operating parameters, system performance, and catalyst service life, considering the catalyst deactivation. Relations between reactor performance, operating parameters, and running time are clarified based on the coupling analysis of the reactions, catalyst deactivation kinetics, and mass/energy balance. The influence of reactor fluctuation on energy cost and product output is explored by topological analysis, pinch analysis, and algebraic reasoning. A reactor-separator-heat exchanger network coupling frame is established to predict system performance and guide the reactor selection, catalyst regeneration, and system adjustments. The proposed method is intuitive and efficient and can be applied in the preparatory/operation stage. For the studied benzene hydrogenation process, the Plug Flow Reactor is suitable; the catalyst’s optimal service life is 2.08 y, achieving 4.4 % and 4.8 % decreases in annual cost and energy demand/carbon emission by real-time adjustments.

Deeply revealing the mechanism of the synergistic effect of Cu and P on alleviating CaO poisoning performance of V-W-Ti catalysts in cement kilns

CaO was the inevitable cause of V2O5-WO3-TiO2 catalyst (VWTi) poisoning in cement kilns. The significant reduction in NO conversion was due to the combination of CaO and active species of the vanadium-based catalyst. In this work, the VWTi catalysts were modified with different contents of Cu and P to improve resistance to CaO, thereby extending the service life of catalysts in cement kilns. By doping Cu and P, the Ca-VWCu3P5Ti had better catalytic activity, reduced the poisoning effect of CaO to V5+, thus protecting the redox properties and increasing the surface acidic sites of the catalyst. Meanwhile, the in-situ DRIFTs results showed that the poisoning effect of CaO was weaker on the Ca-VWCu3P5Ti than that of the Ca-VWTi. In addition, the NH3 and NO species could be effectively adsorbed and activated on the surface of the Ca-VWCu3P5Ti by E-R mechanism. In this way, the harm of CaO to the vanadium-based catalysts was effectively reduced. This work provided a promising strategy to design vanadium-based catalysts with superior resistance to CaO in NH3-SCR reaction.

Rapid charge migration of hierarchical S-Scheme g-C3N4/CdS@C for efficient photocatalytic hydrogen evolution

Photocatalytic H2 evolution as a resultful way to figure out energy problems is still inhibited by carrier separation efficiency and catalyst service life. Here, we report a hierarchical S-Scheme heterostructure of layered graphite carbon nitride and CdS nanoparticles coated with carbon film (g-C3N4/CdS@C) by a simple hydrothermal method for highly efficient visible-light-driven H2 evolution. The S-Scheme, comprising g-C3N4 and CdS, synergistically enhances the efficiency of carrier separation while maintaining the redox capacity of both components. The introduction of carbon film enhances the migration rate of carriers, in the meantime inhibits the photo corrosion of CdS to enhance the stability of catalyst. The g-C3N4/CdS@C achieves the H2 generation rate of 6.4 mmol g−1 h−1 and the apparent quantum yield of 12.7%, superior to most works on g-C3N4. This work provides a delicate S-Scheme photocatalyst and offers a valid strategy for prolonging the lifetime of transition metal sulfide-based materials.

NOx reduction over catalysts with inborn resistance to multipoisons

Selective catalytic reduction (SCR) of NH3 is a widely used technology for eliminating NOx, but alkali metals, heavy metals, SO2, and other flue gas contaminants can drastically reduce the service life of catalysts and increase the cost of environmental protection. This study demonstrates that the TiOSO4/CeO2 catalyst exhibits natural resistance to multipoisons for NOx reduction. Despite being poisoned with 1 wt% K2O and 3 wt% PbO, the catalyst retained a NOx conversion rate of over 95% across a wide temperature range of 225–450 °C and showed excellent tolerance to SO2. The catalyst's interfacial structure is composed of cross-linked TiO6-SO4-Ce-O units. When K&Pb were deposited on the TiOSO4/CeO2 catalyst, the SO42- ions distributed on the catalyst surface preferentially combined with K&Pb to protect the Ce active sites. Additionally, the cross-linked TiO6 layer structure on the catalyst surface effectively blocked the adsorption of SO2. This anti-poison strategy enhances NOx reduction and resistance by modifying intrinsic active sites, rather than constructing additional sacrificial sites traditionally. These findings have significant implications for the development of effective NOx reduction catalysts with excellent resistance to multipoisons for practical applications.

Combination of porous covalent triazine frameworks with spinel for highly improved photothermal catalytic oxidation of toluene

The synergistic effect of adsorption and photothermal can be used to develop new efficient pollutant treatment technologies. Here, porous covalent triazine frameworks modified CuO@CoMn2O4 catalyst (PCTF-CCM) was constructed and applied to the full spectrum driven photothermal degradation of toluene. Toluene conversion and CO2 yield over PCTF-CCM under simulated solar irradiation (optical power density=350 mW/cm2) could be reached 100% and 98% with 40 min. Oxygen vacancies play an important role in thermal and photothermal catalysis by enhancing the adsorption of pollutant gases and the mobility of oxygen. The porous covalent triazine frameworks enriched the concentration of pollutants on the surface of catalyst and significantly improved the water resistant capability, leading to the performance of photothermal catalytic oxidation of toluene highly improved. The designed system extends the range and service life of catalyst in practical applications and provides a new idea for the design of adsorption-photothermal catalyst.

The Preparation Processes and Influencing Factors of Biofuel Production from Kitchen Waste

Kitchen waste is an important component of domestic waste, and it is both harmful and rich in resources. Approximately 1.3 billion tons of kitchen waste are produced every year worldwide. Kitchen waste is high in moisture, is readily decayed, and has an unpleasant smell. Environmental pollution can be caused if this waste is treated improperly. Conventional treatments of kitchen waste (e.g., landfilling, incineration and pulverization discharge) cause environmental, economic, and social problems. Therefore, the development of a harmless and resource-based treatment technology is urgently needed. Profits can be generated from kitchen waste by converting it into biofuels. This review intends to highlight the latest technological progress in the preparation of gaseous fuels, such as biogas, biohythane and biohydrogen, and liquid fuels, such as biodiesel, bioethanol, biobutanol and bio-oil, from kitchen waste. Additionally, the pretreatment methods, preparation processes, influencing factors and improvement strategies of biofuel production from kitchen waste are summarized. Problems that are encountered in the preparation of biofuels from kitchen waste are discussed to provide a reference for its use in energy utilization. Optimizing the preparation process of biofuels, increasing the efficiency and service life of catalysts for reaction, reasonably treating and utilizing the by-products and reaction residues to eliminate secondary pollution, improving the yield of biofuels, and reducing the cost of biofuels, are the future directions in the biofuel conversion of kitchen waste.

Catalytic production of 1,2-propanediol from sucrose over a functionalized Pt/deAl-beta zeolite catalyst.

To eliminate the dependence on fossil fuels and expand the applications of biomass conversion, an efficient Pt/deAl-beta@Mg(OH)2 catalyst was designed, with dealuminated beta zeolite loaded with Pt as the core and Mg(OH)2 as the shell. The catalyst was used to produce 1,2-propanediol (1,2-PDO) from sucrose. The preparation and reaction conditions of the catalyst were optimized. The optimal yield of 1,2-PDO was 33.5% when the conditions were 20 h of dealumination, 3.0 wt% Pt loading, 5.0 wt% Mg(OH)2, 200 mg of catalyst, 10 mL (11.25 mg mL-1) of sucrose solution, an initial H2 pressure of 6 MPa, 200 °C, and 3 h. The core-shell structure of the modified beta zeolite shows good stability, yielding more than 30.0% after three cycles of reuse. Firstly, the molecular zeolite can host more acid sites after dealumination by concentrated nitric acid and this can prolong the catalyst's service life. Secondly, the loading of Pt increases the distribution of acid sites and improves the shape selectivity of the catalyst. The introduction of alkali produces many alkaline sites, inhibits the occurrence of side reactions, and increases the product yield. The above modification methods increase the production of 1,2-PDO by promoting isomerization between glucose and fructose from sucrose hydrolysis and the reverse aldol condensation (RAC) reaction. This paper provides a theoretical basis and reference route for applying biomass conversion technology in practical production, which is of great significance for developing biomass resources into high-value-added chemical products.

One-Dimensional Numerical Simulation of Pt-Co Alloy Catalyst Aging for Proton Exchange Membrane Fuel Cells

The service life of catalysts is a key aspect limiting the commercial development of proton exchange membrane fuel cells (PEMFCs). In this paper, a one-dimensional degradation model of a Pt-Co alloy catalyst in the cathode catalytic layer (CCL) of a PEMFC is proposed, which can track the catalyst size evolution in real time and demonstrate the catalyst degradation during operation. The results show that severe dissolution of particles near the CCL/membrane leads to uneven aging of the Pt-Co alloy catalyst along the CCL thickness direction. When the upper potential limit (UPL) is less than 0.95 V, it does not affect the catalyst significantly; however, a slight change may cause great harm to the catalyst performance and service life after UPL > 0.95 V. In addition, it is found that operating temperature increases the Pt mass loss on the carbon support near the CCL/membrane side, while it has little effect on the remaining Pt mass on the carbon support near the CCL/GDL side. These uncovered degradation mechanisms of Pt-Co alloy provide guidance for its application in PEMFCs.

Optimization of the catalyst service life based on the coupling of reactor and heat exchanger network

A systematic method is proposed for targeting the optimal catalyst service life, considering the catalyst deactivation and coupling integration of HEN and reactor. Relations among the reactor’s conversion, inlet/outlet temperature, energy consumption, average product cost, and catalyst activity are determined based on the catalyst deactivation kinetics, energy balance, and the migration of the composite curves. The Reactor-HEN coupling diagram is constructed to illustrate the variation curves of these indexes with catalyst activity/catalyst regeneration activity and target the optimal regeneration activity. The optimal catalyst service time is further determined considering the catalyst deactivation dynamics. A practical process with benzene hydrogenation to cyclohexene is studied. The optimal regeneration activity of the Ru-Zn-B/ZrO2 catalyst is determined to be 0.42, and the optimal service life is 1.32 y. The proposed method is efficient, and the results can guide the design and operation of the production processes.

Pt@SAPO-11 bifunctional catalysts with spatial architecture constructed via a seed-directed solvent-free strategy for n-dodecane hydroisomerization

Inferior sintering-resistance of metal nanoparticles is an obstacle restricting the development of bifunctional catalysts in chemical industry. The construction of spatial architecture in zeolitic framework can enhance the stability of metal nanoparticles and prolong the service life of catalysts. A seed-directed solvent-free strategy was proposed here to prepare a metal-confined catalyst along the zeolitic framework to sterically encapsulate metal nanoparticles. The use of raw materials without extra solvents could improve synthetic efficiency of each kettle, reduce economic cost and decrease environmental pollution caused by organic solvents. The status of metal species was observed by aberration-corrected TEM images and XPS spectra, and the intracrystalline Pt species were speculated to isomorphically substitute the framework Al and P or occupy tens of micropore to form structural defect sites, leading to a decrease in the support acidity and a better balanced bifunctionality. While enhancing the metal stability, the maximum yield of isomer products was increased to 75% versus 63% for the conventional specimen synthesized by hydrothermal and post-impregnated method on n-dodecane hydroisomerization. The results provide an efficient route to the synthesis of alternative bifunctional catalysts for n-alkanes hydroisomerization, and promote the high value-added conversion of downstream products in coal/natural gas chemical industry.

Visible-light activation of sulfite by ZnFe2O4@PANI photocatalyst for As(III) removal: The role of radicals and Fe(IV)

Inorganic arsenic (As) exists widely in industrial wastewater and poses a serious risk to human health. Here, sulfite was employed to enhance the photocatalytic oxidation ability, and As(III) containing wastewater was rapidly purified within 30 min. Furthermore, this photocatalytic system maintain excellent performance at wide pH range of 3–10. By measuring intermediate radicals and ions, pH-dependent mechanism of sulfite activation was proposed. Under acid conditions, sulfite radicals (•SO3-) were detected in photocatalytic system, and quickly convert into oxidizing radicals (•SO4- and •OH), which were responsible for As(III) oxidation. While at alkaline conditions, only tetravalent iron [Fe(IV)] was detected as oxidizing substance contributing to As(III) removal during photo reaction process. Moreover, Fe(IV) mainly existed on catalyst surface rather than solution, the limited Fe leaching could extend the service life of catalyst, which should be attributed to the core–shell structure of ZnFe2O4@PANI. These findings in this work advances the fundamental understanding of radicals conversion and Fe(IV) formation during sulfite activation process.

Model Fuel Oxidation in the Presence of Molybdenum-Containing Catalysts Based on SBA-15 with Hydrophobic Properties.

We have studied for the first time the role of hydrophobicity of the mesoporous silicate SBA-15 on the activity and the service life of a catalyst in the peroxide oxidation of sulfur-containing compounds. Immobilization of the molybdate anion on the SBA-15 support via ionic bonding with triethylammonium groups allows us not only to decrease the reaction temperature to a relatively low value of 60 °C without a drop in the dibenzothiophene conversion degree but also to increase the service life of the catalyst to many times that of the known analogs. The support and catalyst structures were investigated by low-temperature nitrogen adsorption/desorption, Fourier-transform infrared spectroscopy, X-ray fluorescence analysis, and transmission electron microscopy. Immobilization of the molybdate anion on the SBA-15 support, modified with ammonium species, prevents the leaching of active sites. However, only alkyl-substituted ammonium species minimize DBT sulfone adsorption, which significantly increases the catalyst’s service life. The synthesized catalyst Mo/Et3N-SBA-15 with hydrophobic properties is not sensitive to the initial sulfur content and hydrogen peroxide amount and retains its activity for at least six cycles of oxidation without regeneration. These catalysts can be efficiently used for clean fuel production.

Nb-MCM-Type Mesoporous Material Synthesis Using Ionic Solid as Structure-Directing Agent for In Situ Lipase Immobilization.

MCM-41 and MCM-48 with niobium were successfully synthesized using 1-tetradecyl-3-methylimidazolium chloride ([C14MI]Cl) as a structure-directing agent. The best Si/Nb molar ratio was chosen (Si/Nb = 20) and the CALB enzyme was immobilized in situ in the synthesized Nb-MCM. SEM micrographs showed the formation of very regular spherical agglomerates with a diameter between 0.25 and 0.75 μm. The material presented a surface area of 954 and 704 m2/g and a pore volume of 0.321 and 0.286 cm3/g, for Nb-MCM-41 and Nb-MCM-48, respectively. Also, both materials showed a pore size of 2.261 nm. The number of recycles obtained for the CALB enzyme immobilized in Nb-MCM-41 and Nb-MCM-48 was 26 recycles with a residual activity of 49.62% and 16 recycles with a residual activity of 53.01%, respectively. For both materials, enzymatic activity remained stable for 5 months of storage at room temperature and refrigeration. The supports were able to catalyze the esterification reaction at 40, 60, and 80 °C, showing industrial application in reactions that require high temperatures. This methodology allows the preparation of new highly active and selective enzyme catalysts using niobium and [C14MI]Cl. Also, the new materials can provide greater viability in processes, ensuring a longer service life of catalysts. Graphical abstract.

The denitration mechanism of fly ash catalysts prepared by low-temperature plasma technology

In this paper, fly ash-based catalysts were supported by equivalent-volume impregnation method and roasted with low-temperature plasma technology. This technology has the advantages of short treatment time, lower energy consumption, and well-distributed active components. Therefore, the plasma power, plasma time, oxygen flow rate and metal loading condition in the denitration process were studied at sub-atmosphere ambient gas processing conditions. Different types of fly ash, modification conditions and loading conditions in the denitration process were studied. BET, XRD, SEM and XPS were used to characterize the catalysts, and the effect of the structure and performance of catalysts during the catalytic activity of the catalysts were further determined. The results were: The manganese metal and cerium metal were successively loaded in the catalyst and then roasted in low temperature plasma with oxygen. The two metals had a synergistic effect on forming P-type semiconductors, which significantly improved the performance of denitration. MnO2 and CeO2 played a major role in denitration. The fly ash-based catalyst with the preliminary modification and then loaded metal oxides not only maintained effective denitration performance, but also greatly improved the sulfur resistance, and had a positive effect on extending the service life of catalysts.

In-situ Quantification of Nanoparticles Oxidation: A Fixed Energy X-ray Absorption Approach

The oxidation of palladium nanoparticles causes the performance degradation of alkaline direct ethanol fuel cells. Quantifying this oxidation is a task of tremendous importance to design mitigation strategies that extend the service life of catalysts and devices. Here, we show that the Fixed Energy X-ray Absorption Voltammetry (FEXRAV) can provide this information with an in-situ approach. To do so, we have developed a quantification method that assumes the linear response at fixed energy. With this method, we have investigated the oxidation of carbon black-supported palladium electrocatalysts during cyclic voltammetry in the same solution employed as a fuel in the direct ethanol fuel cells. We have shown that up to 38% of the palladium is oxidised at 1.2 V vs RHE and that such oxidation also happens at lower potentials that the catalyst can experience in real direct ethanol fuel cells. The result of this study is a proof of concept of quantitative FEXRAV.

Unsteady-state mathematical model of diesel fuels catalytic dewaxing process

In this work, the mathematical model of the process of diesel fuels catalytic dewaxing was developed. Calculations on the mathematical model show the effect of temperature, feedstock composition and catalyst activity on the catalytic dewaxing process. It was established that operation of the process under optimal conditions, determined by calculations on the mathematical model, increases the catalyst service life by 6%.

Comparative analysis of catalyst operation in the process of higher paraffins dehydrogenation at different technological modes using mathematical model

This paper presents the results of comparative analysis of three run cycles of platinum catalyst for higher paraffins C9–C14 dehydrogenation process, performed using mathematical model. The results of model calculations were compared with the experimental data obtained at the industrial unit. It was established that deactivation of the platinum dehydrogenation catalyst is influenced by the technological modes of its operation, such as temperature, pressure, hydrogen/feedstock molar ratio and water supply. In the process of higher paraffins dehydrogenation, the phenomenon of platinum catalyst self-regeneration is observed. This occurs due to the action of feedstock components, in particular water and hydrogen involved in oxidation and hydrogenation of intermediate condensation products (coke structures). Model calculations showed that with a decrease in the hydrogen/feedstock molar ratio and simultaneous increase in water supply, depending on the temperature and composition of feedstock, it is possible to slow down deactivation process and increase the catalyst service life. This fact was experimentally confirmed at industrial unit.

Application of Oxidative Regeneration of Zeolite-Containing Catalysts to Solid-Acid Alyklation of Isobutane by Olefins

Application of oxidative regeneration of zeolite-containing catalysts to alkylation of isobutane by olefins was investigated during long-term catalyst tests at a pilot plant. This approach to regeneration was found to shorten the catalyst service life between regenerations. Local overheating of the catalyst is presumed to cause irreversible sintering and, as a result, a decrease of alkylate yield

Light-dependent controlled synthesis and photocatalytic properties of stable Ag3 nanocrystals

The silver phosphate (Ag3PO4) is applied in organic matter photodegradation as a novel catalyst materials, however, its instability reduces the photocatalytic life and limits its further applications. In this work, a series of Ag3PO4 crystalline nanoparticle clusters have been synthesized by a photocontrol method. By comparing their sunlight photocatalytic properties, the Ag3PO4 nanoparticles with dominant {220} facets have a lower surface energy (1.05Jm−2) than existing Ag3PO4 crystals which can offer a longer catalyst service life. The photodegradation rate of the Ag3PO4 nanoparticles is about 3 times that of common Ag3PO4 bulk materials and the sunlight is used as the power source instead of high cost artificial visible light sources in this catalytic system. An effective continuous photodegradation reactor using Ag3PO4 nanoparticles is successfully fabricated to degrade rhodamine B solution. At the same time, this work provides an example for how oxidation photocatalyst works without extra adding sacrificial reagent.

Methods of increasing the stability of the catalytic effect of MFI type zeolites and the total service life of catalysts based on them

Increasing the operational stability of MFI-type zeolite catalysts is topical for the creation of highly efficient catalysts for the conversion of methanol or C2-C4 hydrocarbon gases into aromatic hydrocarbons, i.e., important industrial processes. This study proposes three new approaches to increasing the stability of zeolite catalysts: selective dealumination on the outer surface of MFI zeolite crystals, structurally selective ion exchange on the outer surface of crystals, and the application of an isothermal (multitube) reactor. The effect of selective dealumination and structurally selective ion exchange conditions on the SiO2/Al2O3 molar ratio in the zeolite on the interregeneration period duration in the conversion of methanol into hydrocarbons has been studied. It has been established that the selective dealumination of the outer surface increased the interregeneration period duration by 3–5 times. Structurally selective ion exchange on the outer surface of zeolite crystals allows us to increase the interregeneration period duration by 2–4 times and to decrease the regeneration temperature and duration due to the change of the properties of deposited coke. The application of a multitube reactor facilitates the procedure of regeneration in comparison with an adiabatic reactor due to the formation of less condensed coke depositions.