Problem Of Catalyst Deactivation Research Articles

Covalently bridge metals to biomass carbon for sensing DA and FA with high specificity and sensitivity

Due to the high catalytic activity and electrical conductivity, “transition metal-nonmetal” compounds have broad application prospects in the construction of electrochemical sensors. However, it is still a challenge to solve the problem of catalyst deactivation and slow electron transfer due to nanoparticle agglomeration's blockage of active sites. Here, we prepare a series of covalently bonded “C-M-O” bridge bonds on biomass carbon for the first time. The bridge bonds have a straight-like “electron path”, which shortens the electron transfer path and improves the electrical conductivity, and catalytic activity. The bridge bonds exhibit excellent catalytic activity even after being subjected to prolonged mechanical external forces. Besides, the bridge bonds can integrate a biosensor with MIP and exhibit excellent electrocatalytic performance, including high sensitivity, low detection limit, excellent stability, superior interference immunity, and the ability to accurately monitor DA and FA released from real samples and live cells in real time. The strategy of forming “C-M-O” bridge bonds based on covalently bonded supports provides a new perspective for solving the agglomeration of nanocatalysts blocking active site deactivation and improving electron transfer rate.

Low-temperature catalytic performance improvement of Ru/TiO2{001} for o-dichlorobenzene oxidation

Chlorinated aromatics hydrocarbons were harmful to ecology and human health, whose catalytic combustion encounters problem of catalyst deactivation by chlorine poisoning. To simultaneously improve the catalytic activity, CO2 selectivity and stability of catalyst, the present study used the loading of Ru active component on the anatase TiO2 which preferentially exposes highly active {001} crystalline facets. Take o-dichlorobenzene (o-DCB) oxidation as a surrogate reaction, Ru/TiO2{001} showed lower T90% (temperatures with 90% conversion), higher CO2 selectivity and better stability than Pt/TiO2{001}, Pd/TiO2{001} and Ru/commercial TiO2 (Ru/TiO2-C). The excellent results could be attributed to the strong metal support interaction between Ru species and TiO2{001}, with more oxygen vacancies and higher surface oxygen concentration, more Lewis acid sites, enhanced low-temperature reducibility, more surface Ti3+ species, more surface Ru4+ species, and highly dispersed Ru species, favoring the excellent low temperature catalytic activity and CO2 selectivity of Ru/TiO2{001}. In addition, the less Cl species on the used 1.5% Ru/TiO2{001} indicated their effectively removal, which is the core issue for the deep oxidation of o-DCB. Furthermore, the in situ FTIR spectroscopy gave the detail oxidation route of o-DCB over 1.5% Ru/TiO2{001}, that the co-adsorption of o-DCB and O2 on Ru/TiO2{001} surface were calculated based on the density functional theory calculations. The present study gave a new insight into the new pathway for the design of promising catalysts for the treatment of CAHs.

Microwave controlled ignition and combustion characteristics of ADN-based ionic liquid propellant with fast response and environmental friendliness

The ADN-based ionic liquid propellants have been successfully implemented in liquid rocket engines, owing to high specific impulse and thrust, low toxicity and environmental friendliness. However, the traditional catalyst ignition of ADN-based propellant suffers from the problems of catalyst deactivation problems in the heating process. Microwaves could interact with the material holistically due to excellent penetration ability. Compared with solid materials, ionic liquids are natural microwave receptors on account of great polarity. To date, the possibility of microwave ignition of ionic liquid materials has not been explored. In this work, two kinds of ionic liquids: ADN and [AMIM][DCA] were used as oxidant and fuel of liquid propellant to achieve the maximum microwave absorption effect. The microwave controlled ignition and combustion of ADN-based liquid propellant was first realized and systematically studied. Compared to single component, the heat release, gas production, conductivity and heating rate of the mixed system was greatly enhanced. The sample (ADN/[AMIM][DCA] 10%) was successfully ignited by microwaves, displaying a decreased ignition delay time at higher power inputs. The ignition was generated in the gas phase and rapidly diffused into the solution, and the extinguishment was highly consistent with the input cessation of microwaves. The ignition delay was significant reduced in repeated ignition, resulted from the faster moving speeds of ions. The successful realization of microwave controlled ignition and combustion of ADN-based IL propellant will broaden the scope of their applications in space fuel and provide a new direction for the reform of liquid engines.

Deactivation Mechanism and Anti-Deactivation Measures of Metal Catalyst in the Dry Reforming of Methane: A Review

In recent decades, the massive emission of greenhouse gases, such as carbon dioxide and methane, into the atmosphere has had a serious impact on the ecological environment. The dry reforming of carbon dioxide and methane to syngas cannot only realize the resource utilization of methane and carbon dioxide but also reduce global climate change. It is of great significance in carbon emission reduction. Owing to the dry reforming of methane (DRM) being a strongly endothermic reaction, it needs to be carried out under high-temperature conditions. It makes the catalyst have problems of the sintering of metal, carbon deposition, and poisoning. This article revolves around the problem of catalyst deactivation during the DRM reaction. It expands upon the thermodynamics and mechanisms of the DRM reaction, analyzes the causes of metal catalyst deactivation due to carbon deposition, sintering, and poisoning, and summarizes how the active components, supports, and additives of metal catalysts restrain the DRM catalyst deactivation during the reaction. The analysis revealed that changing the type and size of the active metal, adjusting the properties of the support, and adding additives can further regulate the dispersion of the active component, the interaction between the active component and the support, the oxygen vacancies of the support, and the acidity and basicity of the catalyst surface, ultimately achieving control over the metal catalyst’s resistance to sintering, carbon deposition, and sulfur poisoning. In addition, it discusses the application of metal catalysts in photothermal and plasma-catalyzed DRM. Finally, it outlines the prospects for research on metal catalysts for the DRM.

Hydrogen and aromatics recovery through plasma-catalytic pyrolysis of waste polypropylene

Plasma-catalysis pyrolysis is a promising way to solve the problem of catalyst deactivation during plastic recycling. In this study, pyrolysis of polypropylene (PP) over zeolite ZSM-5 has been carried out in a two-stage fixed bed pyrolysis system with a coaxial dielectric barrier discharge (DBD) plasma reactor. The role of plasma on the pyrolysis process, as well as the stability of the plasma-catalytic system was investigated. Compared to conventional catalytic pyrolysis, plasma-catalysis pyrolysis increased gas products from 29 wt% to 47 wt% with 4.19 mmol/g H2 formed, and improved the selectivity of BTX (benzene, toluene, xylene) whilst inhibiting the production of wax simultaneously. After 10 cycles, clear decreases in gas and oil yield (from 86 wt% to 48 wt%) and BTX selectivity (from 71 wt% to 39 wt%) were found in the conventional catalytic pyrolysis, however, nearly no variation was shown in the plasma-catalysis mode. The coupling of catalyst and plasma modified the catalysts acidic sites, while the radicals enhanced the pre-cracking of volatiles, resulting in less deposited coke. Overall, the introduction of plasma resulted in an obvious reduction in total costs and presented a feasible strategy for the recycling of waste plastic.

Hydrothermal treatment of metal impregnated biomass for the generation of H2 and nanometal carbon hybrids

The nanocatalyst impregnation onto the biomass matrix has gained importance in enhancing the H2 yield and overcoming the catalyst deactivation problems. In-situ catalytic gasification of Ru/Fe-impregnated sugarcane bagasse and citrus limetta (mosambi peels) were examined and compared with their raw biomass at subcritical and supercritical water conditions. Bagasse having a higher amount of lignocellulosic content produces a maximum yield of H2 over moambi peels. Besides, Ru and Fe nano-metal carbon hybrids with crystalline sizes between 10 and 25 nm were formed during in-situ hydrothermal gasification. The performance of hydrothermal gasification based on hydrogen yield was studied, and it relatively follows the order as temperature, nanoparticle composed, metal loading onto biomass matrix, type of catalyst, and biomass used. At the maximum operating temperature of 600 °C, B: W ratio 1:10 for the resident time of 60 min, highest H2 yield of 12.75 ± 0.17 and 11.20 ± 0.13 mmol/g attained for Ru and Fe impregnated bagasse with the CGE of 72.28 ± 2.17% and 67.08 ± 1.97% respectively. At similar operating conditions, H2 yields of 8.75 ± 0.18 and 8.13 ± 0.16 mmol/g were achieved with the CGE of 62.4 ± 1.91% and 53.7 ± 1.66% for Ru and Fe impregnated mosambi peels, respectively. Based on the H2 and CH4 production, Ru shows the highest performance than Fe catalyst.

Recent progress in ceria-based catalysts for the dry reforming of methane: A review

The mitigation of CO2 and CH4 emissions is feasible by transforming them into valuable syngas via the dry reforming of methane (DRM). However, the problem of catalyst deactivation has restricted its industrial application. Therefore, the development of catalysts for an effective reforming process has been attracted enormous attention. Ceria has a high potential as it can serve as both catalyst support and metal active site for adsorption and dissociation of CO2 and CH4. Material properties, such as redox and acid/base properties, and oxygen storage capacity, greatly affect catalytic behavior and performance, as well as coke inhibition in the DRM. This review aims to provide an up-to-date summary on the DRM over ceria-based catalysts, including aspects of the catalysts, reaction mechanism, deactivation, and regeneration studies. This review also proposes governing factors and new ways for improving the process, to provide a more rational to designing an ideal ceria-based catalyst for DRM.

Regeneration mechanism of a deactivated zeolite-supported catalyst for the combustion of chlorinated volatile organic compounds

Industrial catalysis is confronted with the common problem of catalyst deactivation.

Improved conversion efficiency of Lignin-to-Fuel conversion by limiting catalyst deactivation

Herein, the lignin-to-fuel conversion process was studied using real lignin as feedstock. Unlike model compounds, real lignin poisons the catalyst, causing rapid deactivation. The problem of catalyst deactivation was analyzed in detail for improving the conversion efficiency. We found that heavy carbonaceous deposits on the inner surface of the catalyst were responsible for the fast deactivation encountered in the conventional one-step reaction process. Moreover, the ester structures in lignin, which have previously been neglected in research, were confirmed to considerably worsen catalyst deactivation because they induce easier polymerization and hinder lignin conversion. Based on these points, we developed a three-step method that eliminates serious catalyst deactivation in the lignin-to-fuel conversion process, involving depolymerization of lignin, extraction of lignin monomers and hydrodeoxygenation of lignin monomers. The fuel production was 8.1–17.6-times more efficient using this three-step method than using the one-step batch reaction.

A review of aerobic glycerol oxidation processes using heterogeneous catalysts: a sustainable pathway for the production of dihydroxyacetone

ABSTRACT The world’s biodiesel increasing production is leading to the accumulation of its main by-product, crude glycerol, with almost no economic value, which valorization is crucial to increase biodiesel production sustainability and competitiveness. Glycerol is a potential platform chemical, with several valorization routes identified. Among them, selective catalytic aerobic oxidation is an attractive and sustainable solution, as high added value products ensure the process robustness against raw material price fluctuations. When glycerol’s secondary hydroxyl group is selectively oxidized, dihydroxyacetone (DHA) is obtained. DHA is a high added value compound, used in cosmetics as the active compound in sunless skin tanning lotions, and its current industrial production by bio-fermentation is not satisfactory; therefore a more efficient production process is needed to overcome the market deficit. The state-of-the-art of DHA production by glycerol aerobic catalytic oxidation in the liquid phase with water as solvent was reviewed and, although it is still in the lab-scale phase, some routes to reach a robust commercial application were already suggested. For DHA production, catalysts should be active under base free conditions, in order to achieve high DHA selectivity. Promoted Pt nanoparticles, as Pt-Bi and Pt-Sb supported in carbon and mesoporous materials, and Au nanoparticles, supported late transition metal oxides as Au/CuO and Au/ZnO, are among the most promising catalysts for high DHA yield processes. For a better understanding of the main variables associated with this process, the effect of catalyst support, particle size, preparation and activation methods, and catalyst deactivation problems were analyzed. In addition, the reaction conditions effect in catalyst performance, including the presence of crude glycerol impurities was considered. Finally, the main studies regarding DHA continuous flow production were reviewed, identifying the major obstacles to overcome, so that commercial DHA production processes through glycerol aerobic catalytic oxidation can finally be implemented.

Metal-organic framework (MOF)-derived catalysts for Fischer-Tropsch synthesis: Recent progress and future perspectives

Fischer-Tropsch Synthesis (FTS) is an important catalytic chemical reaction that converts a mixture of CO and H2 (syngas) derived from biomass, coal or natural gas into ultra-clean fuels or value-added chemicals. However, most traditional catalysts used in the Fischer-Tropsch process are faced with the problems of high deactivation rate triggered by sintering, phase changes and oxidation which hamper their catalytic performance. Metal-organic frameworks (MOFs)-derived materials have been a promising alternative in addressing the catalyst deactivation problems in FTS because of the encapsulation of their metal nanoparticles in carbon matrix and absence of large particle size, among other reasons. Therefore, this review emphasizes the most recent research headway in the investigation of MOFs as precursors to achieve high-performance FTS catalysts. Precisely, the design of iron and cobalt-based FTS catalysts from parent MOFs via MOF-mediated synthesis, the catalytic activity of the MOF-derived materials and the promoter effects under FTS operation were outlined and discussed. We have also evaluated the influence of MOF structures on the FTS performance and compared them with traditional/commercially available catalysts to show the importance of this approach. Finally, the challenges and opportunities to further expedite the extensive research efforts and promote their applications in material design and FT technology were mentioned.

The Interaction of NH4HSO4 with Vanadium–Titanium Catalysts Modified with Molybdenum and Tungsten

With the wide application of selective catalytic reduction (SCR) systems in power plants for the control of NOx emission in China, a serious problem of catalyst deactivation due to the channel blockage by NH4HSO4 has drawn extensive attention. In this work, a combined experimental and simulation method was utilized to study the interaction between NH4HSO4 and a vanadium–titanium-based catalyst. Initially, the adsorption characteristics of NH4HSO4 onto TiO2, V2O5/TiO2, V2O5-WO3/TiO2, and V2O5-MoO3/TiO2 were simulated following density functional theory. The simulation revealed that during reaction, the NH4HSO4 loaded onto TiO2 can be dissociated into NH4+ and SO42–. The existence of V2O5, WO3, and MoO3 can form a protective layer to inhibit the adsorption of NH4HSO4 onto TiO2, to promote the reduction of sulfur-containing compounds, and to accelerate the reaction of NH4+ with NO. Thermogravimetric analysis also showed the positive effect of V, W, and Mo on NH4HSO4 decomposition. Fixed-bed experiments were then conducted to compare the performance of the studied catalysts and the effect of NH4HSO4 on their performance. It was proven that the V-5Mo/TiO2 catalyst showed better performance at low temperatures. On the V-5Mo/TiO2 catalyst, ∼78 wt % NH4+ in NH4HSO4 was attached onto Lewis acid sites, which can accelerate the reduction reaction of NO by NH4+. Meanwhile, SO42– can comparatively be easily decomposed at lower temperatures.

Эффективность использования гетерополисоединений типа (NH4)2[Co(H2O)4]2[Mo8O27]∙6H2O в качестве катализаторов для получения этилена

Carrying out heterogeneous acid catalysis with the use of heteropoly compounds has received considerable attention due to the great economic and environmental benefits. In spite of this, its industrial application is limited as there are difficulties in catalyst regeneration (settling) caused by its relatively low thermal stability. The aim of present work was to search and select catalysts related to the class of heteropoly compounds for propane cracking, to test the selectivity of the prosses as well as to discuss possible approaches for solving the problem of catalyst deactivation, that can contribute to achieve stable characteristics of solid heteropoly catalysts. Among these approaches are: the development of new catalysts with high thermal stability, the modification of catalysts to promote coke combustion, the inhibition of coke formation on heteropoly compound catalysts during the process, carrying out the reactions in supercritical media and also the cascade reactions using a multifunctional heteropoly catalyst. The obtained catalyst was also studied by physicochemical methods to get deep knowledge about which features of these compounds influence on the catalytic activity. A highly active and selective catalyst for ammonium octomolybdenocobaltate(II) ammonium (NH4)2[Co(H2O)4]2[Mo8O27]∙6H2O was synthesized for cracking associated petroleum gases. The qualitative, quantitative, and structural composition as well as the specific surface area of the obtained catalyst was established by the methods of X-ray diffraction, X-ray phase and fluorescence analysis. It was revealed that ammonium octomolybdenocobaltate(II) crystallizes in a triclinic syngony with cell parameters: а = 8.6292(9) Å b = 9.4795(10) Å c = 12.2071(13) Å α = 104.326(2)° β = 109.910(2)° γ = 100.820(2)°.

Methane Aromatization in a Fluidized Bed Reactor: Parametric Study

Methane aromatization is a promising technology for the transformation of natural gas to liquid products, but suffers the problem of catalyst deactivation by coke. A Two-zone fluidized bed reactor has been proposed as a tool to counteract the catalyst deactivation, by providing continuous catalyst regeneration in the same vessel where the main reaction is carried out. This work shows the effect of the main operating conditions (carburization temperature, reaction temperature, carburization time, nature of regenerating agent and feed flow and height of the hydrocarbon entry point) .

Fluid catalytic cracking technology: current status and recent discoveries on catalyst contamination

ABSTRACT The fluid catalytic cracking (FCC) technology is one of the pillars of the modern petroleum industry which converts the crude oil fractions into many commodity fuels and platform chemicals, such as gasoline. Although the FCC field is quite mature, the research scope is still enormous due to changing FCC feedstock, gradual shifts in market demands and evolved unit operations. In this review, we have described the current status of FCC technology, such as variation in the present day feedstocks and catalysts, and particularly, great attention is paid to the effects of various contaminants of the FCC catalysts of which the latter part has not been sufficiently documented and analyzed in the literature yet. Deposition of various contaminants on cracking catalyst during FCC process, including metals, sulfur, nitrogen and coke originated from feedstocks or generated during FCC reaction constitutes a source of concern to the petroleum refiners from both economic and technological perspectives. It causes not only undesirable effects on the catalysts themselves, but also reduction in catalytic activity and changes in product distribution of the FCC reactions, translating into economic losses. The metal contaminants (vanadium (V), nickel (Ni), iron (Fe) and sodium (Na)) have the most adverse effects that can seriously influence the catalyst structure and performance. Although nitrogen and sulfur are considered less harmful compared to the metal contaminants, it is shown that pore blockage by the coking effect of sulfur and acid sites neutralization by nitrogen are serious problems too. Most recent studies on the deactivation of FCC catalysts at single particle level have provided an in-depth understanding of the deactivation mechanisms. This work will provide the readers with a comprehensive understanding of the current status, related problems and most recent progress made in the FCC technology, and also will deepen insights into the catalyst deactivation mechanisms caused by contaminants and the possible technical approaches to controlling catalyst deactivation problems.

Formation of carbonaceous deposits on Pd-based hydrodechlorination catalysts: Vibrational spectroscopy investigations over Pd/Al2O3 and Pd/SOMS

The widespread utilization and commercialization of hydrodechlorination (HDC) over Pd-based catalysts as a remediation technique has been impeded because of catalyst deactivation problems such as formation of carbonaceous deposits under the reductive environment of HDC. In this study, we investigated the use of a novel animated material, swellable organically-modified silica (SOMS), as a catalyst scaffold for HDC of trichloroethylene (TCE) to develop a catalytic system resistant to carbon formation. The state of aggregation of adsorbed TCE on Pd/SOMS was characterized. It was found that the unique nature of SOMS scaffold caused condensation of adsorbents in the SOMS matrix. This is of particular importance considering the fact that the increase of local concentration of reactants due to condensation may enhance the kinetics of catalytic reactions. To determine the resistance to the formation of carbonaceous materials under reaction conditions, in-situ vibrational spectroscopy experiments (diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and laser Raman spectroscopy) were undertaken over Pd-incorporated SOMS in the absence and presence of water vapor in the reactant stream. The commonly used HDC catalyst Pd/Al2O3 was also studied for comparison purposes. Formation of carbonaceous deposits of different nature were observed over Pd/Al2O3 whereas no detectable carbon formation was observed over Pd/SOMS. It was confirmed that surface hydroxyl groups which are in basic character act as coking agents. The carbon formation resistant behavior of Pd/SOMS is closely related to the nature and low concentration of surface hydroxyl groups.

Glycerol steam reforming with low steam/glycerol ratio in a two-zone fluidized bed reactor

The production of hydrogen from glycerol steam reforming has been studied in several reactors. In conventional reactors the catalyst is deactivated by coke: in fixed bed reactors plugging was observed if a low steam/glycerol ratio was employed, while in fluidized bed reactors it was possible to operate for a longer time-on-stream. The use of a two-zone fluidized bed reactor is studied in this work, as a method to counteract the problem of catalyst deactivation by coke. The glycerol reforming takes place in the upper part of this reactor while the catalyst is simultaneously regenerated in the lower part, where a stream of a regenerating gas is introduced. It has been found that CO2, O2 or H2O can act as regenerating gas in a two-zone-fluidized bed reactor, allowing steady state operation at a water:glycerol molar ratio as low as 1.25. The effect of the operating conditions has been studied and the yield to the main products was compared with the calculated values assuming thermodynamic equilibrium.

Effects of fuel gas addition to Claus furnace on the formation of soot precursors

Claus process is used in oil and gas industry to recover sulfur from H2S rich gas streams. The aromatic contaminants in its feed form soot that clog catalytic beds and deactivate them. Another common problem in this process is flame extinction in the furnace due to low H2S concentration. Therefore, fuel gas (mainly, methane) is added to Claus feed to sustain combustion. However, given that hydrocarbons can form polycyclic aromatic hydrocarbons (PAHs) and soot at high-temperatures in the furnace, fuel gas addition may aggravate the problem of catalyst deactivation. This makes it important to understand the role of fuel gas in forming PAHs and soot in the furnace. In this work, a detailed reaction mechanism consisting of 261 species and 1726 reactions is developed for Claus process including reactions for the interaction of hydrocarbons with S-containing species, and is validated using experimental data from flames and flow reactors. The extent of the conversion of hydrocarbons present in the feed gas to PAHs is reported by simulating the thermal section of Claus process. The variation in PAH profiles with varying fuel gas flow rate is also computed and discussed. The pathways for the formation and destruction of aromatic hydrocarbons are presented.

ChemInform Abstract: Renewable Feedstocks: The Problem of Catalyst Deactivation and its Mitigation

AbstractReview: 72 refs.

Renewable Feedstocks: The Problem of Catalyst Deactivation and its Mitigation.

Much research has been carried out in the last decade to convert bio-based feedstock into fuels and chemicals. Most of the research focuses on developing active and selective catalysts, with much less attention devoted to their long-term stability. This Review considers the main challenges in long-term catalyst stability, discusses some fundamentals, and presents options for their mitigation. Three main challenges are discussed: catalyst fouling, catalyst poisoning, and catalyst destruction. Fouling is generally related to the deposition of insoluble components present in the feed or formed by degradation of the feed or intermediates. Poisoning is related to the deposition of electropositive contaminants (e.g. alkali and alkaline earth metals) on acid sites or of electronegative contaminants (e.g. N and S) at hydrogenation sites. Catalyst destruction results from the thermodynamic instability of most oxidic supports, solid acids/bases, and hydrogenation functions under hydrothermal conditions.