Chemical Deactivation Research Articles

Designing VWTi-based catalysts with K resistance via Ce-S modification for selective catalytic reduction of NOx

Selective catalytic reduction (SCR) with NH3 is the main reaction to eliminate nitrogen oxide, and the access of K+ to the catalyst surface severely deactivates the physicochemical properties. To inhibit the deactivation of the catalyst by potassium (K), we synthesized VWCeSTi. In the current study, the catalyst surface was functionalized with cerium sulfate (Ce-S) as a method to suppress K+ deactivation, and the physicochemical properties of the functionalized catalyst were explored. In VWCeSTi, Ce has a low electronegativity compared with V and W; hence, sulfated Ce has a relatively abundant electronic state. Therefore, the approach of the K+ ion in an electron-deficient state leads to the preferential binding of S with K, forming K2SO4 and inhibiting chemical deactivation. Additionally, the addition of Ce-S resulted in improved NH3 adsorption ability, the amount of defective metal species, and participating oxygen. Thus, the modified (Ce-S) catalyst showed improved SCR performance and increased resistance to K.

Impact of sulfur exposure on high-temperature Cu speciation in SSZ-13 Zeolites

Metal active sites exchanged in zeolites dynamically change speciation under different reaction conditions, resulting in condition-dependent reactivity with gas molecules. This is of particular significance in chemical deactivation, such as sulfur poisoning of Cu-SSZ-13 zeolites used for NH3-assisted selective catalytic reduction (SCR) of NOx in diesel engine exhaust. Here, we employ computational techniques, combined with experiments and spectroscopies, to develop thermodynamic models for sulfur poisoning of zeolite framework-bound Cu dimers that form at high temperatures in Cu-SSZ-13 zeolites as a function of both the Al distribution and reaction conditions. Our results demonstrate that framework-bound Cu dimers that form under high temperature oxidative conditions are particularly susceptible to poisoning by SO2 and SO3. These Cu dimers react more exothermically with SOx species than Cu monomers, forming thermodynamically stable sulfur-containing Cu dimers that require high temperatures for catalyst regeneration.

Catalytic performance of mesoporous Mn-Co-Ti for o-xylene degradation: Mechanistic study under practical conditions

Catalytic combustion of volatile organic compounds from industrial flue gases at low temperatures remains a challenge. Herein, we developed a mesoporous Mn-Co-Ti catalyst for o-xylene degradation by a solvothermal strategy. The optimized Mn0.1Co-TiO2 catalyst possessed a nanoflower structures with a surface area of 83.1 m2/g and mesoporous volume of 0.1191 cm3/g. Mn-doping modulated the electronic interactions between Mn and Co, which promoted the formation of MnCo2O4.5 phase and increased Co3+ and Mn4+ content of the catalyst. The Mn0.1Co-TiO2 catalyst had an improved reduction capacity from 170 to 644 °C, with a maximum H2 consumption of 4.56 mmol/g. The Mn0.1Co-TiO2 catalyst achieved 50% o-xylene conversion at 193 °C at a GHSV of 60,000 h−1, whereas the equivalent catalyst prepared by impregnation required 315 °C for 50% o-xylene conversion. In the presence of NO, the generated NO2 accelerated o-xylene conversion because it promoted the generation of more Mn4+-O-Co3+ active sites and accumulation of intermediates such as maleate and acetate species. NH3 and H2O had slight inhibitory effects on o-xylene conversion, which were attenuated by abundant mesopores and redox ability of catalyst. SO2 gas caused inactive sulfates and chemical deactivation on catalyst surface, thus leading to excessive formation of benzoquinone products.

Solar-driven calcium looping in fluidized beds for thermochemical energy storage

Integration between Concentrated Solar Power (CSP) and Calcium Looping (CaL) is gaining consideration in the perspective of large shares of renewable energy sources, to smooth the variability of non-dispatchable energy input. The scope of this study is to investigate the CaL process for ThermoChemical Energy Storage (TCES), by performing a dedicated experimental campaign in fluidized bed under realistic process conditions suitable for CaL-CSP integration. Chemical deactivation of the limestone-based sorbent has been assessed by measuring the extent of Ca carbonation along iterated calcination/carbonation cycles, correlated with physico-chemical characterization of the sorbent at selected stages of the conversion. Properties that have been scrutinized were particle size distribution, bulk density, and particle size, density, and porosity of bed solids. The attainable values of energy storage density were evaluated as well.A remarkable finding of the experimental campaign is the pronounced synergistic deactivation of limestone when it is co-processed with silica sand. Chemical interaction of CaO with the silica sand constituents at the process temperatures has been scrutinized as possible responsible for the loss of reactive CaO toward CO2 uptake. Post-process of particle density data, together with N2-intrusion porosimetric analysis, and quantitative and qualitative XRD analyses, suggests that the sand/lime interaction induces a strong reduction of the total and reactive sorbent porosity and, in turn, of reactivity.Density-based classification to separate converted and unconverted limestone particles after the carbonation step has been evaluated with the goal of increasing process efficiency, by avoiding the circulation of streams with unreacted particles through the plant. For this purpose, the minimum fluidization velocity of calcined and carbonated particles has been measured after each reaction step at the relevant process temperature.

Chemical deactivation of titanosilicate catalysts caused by propylene oxide in the HPPO process

Reducing the bidentate ether species formed from the chemisorption between PO and acid sites in the TS/H2O2system is key to achieving stable operation of the HPPO process.

Novel PEI@CSH adsorbents derived from coal fly ash enabling efficient and in-situ CO2 capture: The anti-urea mechanism of CSH support

Solid amine adsorption is considered to be the most promising technology for post-combustion CO2 capture, but it still has drawbacks due to the high cost of supports and the easy occurrence of CO2-induced chemical deactivation. Herein, we propose a novel eco-friendly method for realizing efficient and stable solid amine adsorbents. A calcium silicate hydrate (CSH) support with a pore volume of 3.0 cm3 g−1 is synthesized from coal fly ash (CFA) with the pore-expanded assistance of azeotropic distillation, and then the PEI@CSH adsorbents are prepared by impregnation. The adsorption capacity of the prepared 60%PEI@CSH-0.1 adsorbent reaches 198 mg g−1 and exhibits an excellent cyclic stability, with an attenuation of only 1.9% after 10 cycles under ideal regeneration conditions. Even under realistic regeneration conditions, the CO2 uptake remains at 103 mg g−1 after 10 cycles, which shows obvious advantages over that of commercial SiO2 supports. By using FT-IR, solid-state NMR and DFT calculations, we found that the CSH support promotes the conversion of primary amines to secondary amines in PEI molecules, and thus effectively inhibits the inactivation induced by the formation of urea compounds. Therefore, the PEI@CSH adsorbents provide a low-cost and high-efficiency approach for both in-situ CFA utilization and CO2 mitigation inside coal-fired power plants.

Experimental investigation on the methanation of hydrogen-rich syngas in a bubbling fluidized bed reactor utilizing an optimized catalyst

Catalytic methanation processes allow the production of natural gas substitutes on a sustainable and renewable basis. This study investigates the catalytic methanation of syngas from dual fluidized bed steam gasification of biomass in an innovative bubbling fluidized bed methanation reactor with an optimized catalyst. Syngas from conventional gasification and a novel combination with syngas from sorption enhanced reforming were investigated. The applied fluidized bed reactor allowed an almost isothermal operation with optimal reaction temperatures between 320 °C–360 °C. Simultaneously, no chemical deactivation or mechanical attrition during 200 h of operation indicates a high long-term stability of the catalyst. The methane concentration downstream the methanation reactor increased from 43 to 74 vol.-%db through the methanation of a hydrogen-rich syngas produced via sorption enhanced reforming. Simultaneously, the methane yield is doubled to 95% and the hydrogen, carbon monoxide and carbon dioxide conversions are improved. Furthermore, it could be shown that a CO2 content below 1 vol.-%db is feasible in the (raw) synthetic natural gas, allowing grid injection without CO2 separation. The results indicate that sorption enhanced reforming in combination with an optimized fluidized bed methanation can lead to technical and economic improvements in sustainable synthetic natural gas production.

Comparative study on potassium poisoning of Cu-CHA catalysts for NH3-SCR: Stability and transformation of Cu2+ ions

Cu-chabazite based catalysts (Cu-SSZ-13 and Cu-SAPO-34) may suffer from chemical deactivation due to the deposition of alkali impurities on the surface of wall-flow particulate filters. In this work, the resistance of two Cu-CHA catalysts to potassium poisoning was compared, and the key factors affecting preservation and evolution of Cu2+ ions were ascertained based on the experimental characterizations and DFT calculations. The feasibility of atom (Cu and H) at various sites (6MR and 8MR) in different types of zeolites (SSZ-13 and SAPO-34) upon K+ attacking was compared. The stability of isolated Cu2+ ions in the zeolite framework and the aggregates of detached copper species determined the catalytic performance of the poisoned catalysts.

Triplet-driven chemical reactivity of β-carotene and its biological implications.

The endoperoxides of β-carotene (βCar-EPOs) are regarded as main products of the chemical deactivation of 1O2 by β-carotene, one of the most important antioxidants, following a concerted singlet-singlet reaction. Here we challenge this view by showing that βCar-EPOs are formed in the absence of 1O2 in a non-concerted triplet-triplet reaction: 3O2 + 3β-carotene → βCar-EPOs, in which 3β-carotene manifests a strong biradical character. Thus, the reactivity of β-carotene towards oxygen is governed by its excited triplet state. βCar-EPOs, while being stable in the dark, are photochemically labile, and are a rare example of nonaromatic endoperoxides that release 1O2, again not in a concerted reaction. Their light-induced breakdown triggers an avalanche of free radicals, which accounts for the pro-oxidant activity of β-carotene and the puzzling swap from its anti- to pro-oxidant features. Furthermore, we show that βCar-EPOs, and carotenoids in general, weakly sensitize 1O2. These findings underlie the key role of the triplet state in determining the chemical and photophysical features of β-carotene. They shake up the prevailing models of carotenoid photophysics, the anti-oxidant functioning of β-carotene, and the role of 1O2 in chemical signaling in biological photosynthetic systems. βCar-EPOs and their degradation products are not markers of 1O2 and oxidative stress but of the overproduction of extremely hazardous chlorophyll triplets in photosystems. Hence, the chemical signaling of overexcitation of the photosynthetic apparatus is based on a 3chlorophyll-3β-carotene relay, rather than on extremely short-lived 1O2.

Deactivation of phosphorus-poisoned Pd/SSZ-13 for the passive adsorption of NOx

Automotive catalysts can be exposed to various poisonous substances that can cause physical or chemical deactivation. One of such poisons is phosphorous, which originates from lubricant oils. This study focuses on the phosphorus deactivation of Pd/SSZ-13 used as a passive NOx adsorber (PNA). A clear deactivation caused by phosphorus was observed, and it was increased by increasing the content of phosphorous. It was concluded that phosphorous can cause both physical and chemical deactivation. This was evident from XPS analysis, where the presence of phosphorus pentoxide (P2O5) causes physical deactivation whereas metaphosphate (PO3-) and phosphate (PO43-) cause chemical deactivation. Also, it was shown that metaphosphates (PO3-) become the dominant phosphorous species at higher P concentrations. Lesser amounts of O2 were released in P-poisoned Pd/SSZ-13, as was found in oxygen TPD when increasing the P concentration, due to the presence of more PO3- species. Furthermore, XRD and 27Al NMR analyses revealed that phosphorus also interacted with alumina in the zeolite framework by forming Al-O-P species; this was also supported by SEM-EDX, where there was a clear overlap of P with Al and Pd spectra. DRIFTS analysis showed that OH groups in contact with the zeolite structure became contaminated by phosphorus and caused a chemical deactivation of Pd/SSZ-13. It was also found that, during multiple cycles, the PNA capacity decreased for phosphorus-poisoned samples. This was caused by the transformation of P2O5, which causes physical blocking, to PO3-, which interacts chemically with the palladium species.

Pd-based membranes performance under hydrocarbon exposure for propane dehydrogenation processes: Experimental and modeling

In this work, a novel Pd–Ag double-skinned (DS-) membrane is used for the first time in conditions typical of propane dehydrogenation (PDH). This membrane presents a protective layer on top of the H2-selective one, which acts as shield against chemical deactivation and mechanical erosion under reaction conditions. While the protective layer is already been proven as an efficient barrier against membrane erosion in fluidized beds, there is no validation yet under PDH reaction. The DS- membrane performance is compared with a conventional (C-) Pd–Ag membrane under alkane/alkene exposure, at 400–500 °C and 3 bar, to investigate whether the incorporation of the protective layer would be suited for H2 separation in PDH systems, and if coking rate would be affected. The novel membrane shows a H2 permeance of 2.28 × 10−6 mol∙m−2 s−1∙Pa−1 at 500 ᵒC and 4 bar of pressure difference, overcoming the performance of the conventional PdAg one (1.56x∙10−6 mol m−2 s−1∙Pa−1). Both membranes present a stable H2 flux under alkane exposure, while deactivation occurs under exposure to alkenes. A model able to describe the H2 flux through Pd-based membranes is presented to fit the experimental data and predict membrane performance. The model includes mass transfer limitations in the retentate and a corrective inhibition factor to account for the competitive adsorption of hydrocarbon species in the H2 selective layer. The experimental results obtained under alkene exposure deviates from model predictions; this can be attributed to carbon deposition on the surface of the selective layer, as further detected on the DS-membrane by Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Analysis (EDX), which is the main factor for membrane deactivation.

Effects of high octane additivated gasoline fuel on Three Way Catalysts performance under an accelerated catalyst ageing procedure

The adoption of high octane rating fuels in Gasoline Direct Injection (GDI) engines helps to improve fuel economy and thus reduce CO2 emission. However, there is scarce literature regarding the impact of additives used in high octane rating fuels on the performance and durability of the exhaust after treatment components. This work investigates the effects of using an aniline (aromatic amine) octane enhancer added to a commercial gasoline fuel on the activity of a commercial Three Way Catalytic Converter (TWC) coupled to a GDI engine. TWC’s capability in abating gaseous and particle emissions is studied for both the additivated and the baseline fuel during and after a fuel-induced accelerated catalyst ageing procedure. The accelerated catalyst ageing procedure is developed aiming to identify the impact of the engine fuel on the catalyst poisoning, while limiting catalyst thermal deactivation.CO and NO conversion efficiencies in the TWC were close to 100% under the steady-state and transient stoichiometric engine operation for both fuels during and after the catalyst ageing procedure. There was a minor decrease (generally < 10%) in the catalytic conversion efficiency of total HC for the additivated fuel, but not being significant to reflect any TWC chemical deactivation. The aniline type octane enhancer additive did not produce any detrimental effect on the TWC efficiency/performance. This investigation demonstrates that fuels being designed to promote a more efficient GDI engine operation can also enable the reduction of vehicle tailpipe CO2 and pollutant emissions through synergies with the TWC for cleaner road vehicles.

Influence of Biomass Inorganics on the Functionality of H+ZSM-5 Catalyst during In-Situ Catalytic Fast Pyrolysis

In this study, the contamination of H+ZSM-5 catalyst by calcium, potassium and sodium was investigated by deactivating the catalyst with various concentrations of these inorganics, and the subsequent changes in the properties of the catalyst are reported. Specific surface area analysis of the catalysts revealed a progressive reduction with increasing concentrations of the inorganics, which could be attributed to pore blocking and diffusion resistance. Chemisorption studies (NH3-TPD) showed that the Bronsted acid sites on the catalyst had reacted with potassium and sodium, resulting in a clear loss of active sites, whereas the presence of calcium did not appear to cause extensive chemical deactivation. Pyrolysis experiments revealed the progressive loss in catalytic activity, evident due the shift in selectivity from producing only aromatic hydrocarbons (benzene, toluene, xylene, naphthalenes and others) with the fresh catalyst to oxygenated compounds such as phenols, guaiacols, furans and ketones with increasing contamination by the inorganics. The carbon yield of aromatic hydrocarbons decreased from 22.3% with the fresh catalyst to 1.4% and 2.1% when deactivated by potassium and sodium at 2 wt %, respectively. However, calcium appears to only cause physical deactivation.

Al-Modified Ti-MOR as a robust catalyst for cyclohexanone ammoximation with enhanced anti-corrosion performance

The skeleton desilication accompanied by Ti active sites leaching accounts for the dominant chemical deactivation reasons in the alkali liquid-phase ammoximation, which could be retarded by creating a protective Al-rich shell.

Interaction mechanism between Se species in flue gas and V2O5-MoO3/TiO2 catalyst: An in-depth experimental and theoretical study

The deactivation of denitrification catalysts has attracted widespread attention, whereas little is known about the poisoning effect of selenium (Se) species to date. In this study, the influence of element Se (Se0), SeO2 and CaSeO3 on the activity of V2O5-MoO3/TiO2 selective catalytic reduction (SCR) catalyst were evaluated under different temperatures. It was found that under 200 °C Se species had no significant effects on the denitrification efficiency. However, the performances of the catalysts were notably suppressed over 250 °C. The interaction mechanism between Se species and V2O5-MoO3/TiO2 catalyst was unveiled via combined comprehensive characterizations and density functional theory (DFT) calculations. The results indicated that the role of CaSeO3 was mainly physical poisoning and little interaction was observed, while Se0 and SeO2 could cause chemical deactivation because of the strong electron transfer. On the catalyst surface, Se0 could react with V2O5 and MoO3 to form Se4+ species (SeO2, VxSeyOz and MoxSeyOz). The formation of VxSeyOz reduced the acid sites on the catalyst, causing irreversible denaturation of the active component V2O5. The formed MoxSeyOz could protect the V2O5 to a certain extent and decompose at higher temperatures to restore the chemical properties of MoO3. SeO2 could be reduced to Se0 by NH3, forming a SeO2 → Se0 → SeO2 cycle beside the SCR process, which continuously hindered the removal of NOx. As the temperature gradually increased, SeO2 sublimated away from the catalyst, partially restored the catalytic activity.

Chemical deactivation of Selective Catalytic Reduction catalyst: Investigating the influence and mechanism of SeO2 poisoning

Selenium (Se) is a major trace element in coal that can easily volatize and become part of flue gas during the combustion process. Currently, the interactions between SeO2 and Selective Catalytic Reduction (SCR) catalysts remain unclear. In this study, a field test at four coal-fired power plants found that the Se concentration at the SCR inlets were relatively high, with more than 95% present in its gaseous phase. To explore possible interactions between SeO2 and SCR catalyst, a V2O5-WO3/TiO2 (VWTi) catalyst was subjected to various degrees of in situ SeO2 poisoning. A positive correlation between the decreases in catalytic activity and N2 selectivity and an increasing amount of SeO2 deposition was observed. The decreases in NH3-adsorption capacity and strong acid sites activation ability were responsible for the loss in catalytic activity, while higher ratio of chemisorbed oxygen and stronger reducibility resulted in NH3 being oxidized to N2O and N2 selectivity loss. Based on these results, it is clear that SeO2 poisoning of SCR catalysts should be taken into consideration to ensure the reliable operation of SCR systems.

Effect of biofuel- and lube oil-originated sulfur and phosphorus on the performance of Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts

Two different SCR catalysts, V2O5-WO3/TiO2 and Cu-SSZ-13, were exposed to biodiesel exhausts generated by a diesel burner. The effect of phosphorus and sulfur on the SCR performance of these catalysts was investigated by doping the fuel with P-, S-, or P + S-containing compounds. Elemental analyses showed that both catalysts captured phosphorus while only Cu-SSZ-13 captured sulfur. High molar P/V ratios, up to almost 3, were observed for V2O5-WO3/TiO2, while the highest P/Cu ratios observed were slightly above 1 for the Cu-SSZ-13 catalyst. Although the V2O5-WO3/TiO2 catalyst captured more P than did the Cu-SSZ-13 catalyst, a higher degree of deactivation was observed for the latter, especially at low temperatures. For both catalysts, phosphorus exposure resulted in suppression of the SCR performance over the entire temperature range. Sulfur exposure, on the other hand, resulted in deactivation of the Cu-SSZ-13 catalyst mainly at temperatures below 300-350 °C. The use of an oxidation catalyst upstream of the SCR catalyst during the exhaust-exposure protects the SCR catalyst from phosphorus poisoning by capturing phosphorus. The results in this work will improve the understanding of chemical deactivation of SCR catalysts and aid in developing durable aftertreatment systems.

Recognition of the Enzymatically Active and Inhibitive Oxygenous Groups on WO3-x Quantum Dots by Chemical Deactivation and Density Functional Theory Calculations.

The design and construction of efficient nanozymes are vital for bio/chemo-sensing applications, while the systematic catalytic mechanism study is the prerequisite. Tungsten oxide (WO3-x) quantum dots (QDs), an alternative to conventional heavy metal-containing semiconductor QDs, possess peroxidase-like activity but limited catalytic efficiency. Therefore, the functions of the typical oxygenous groups in determining the enzymatic activity of the WO3-x QDs by target-specifically shielding the carboxyl (-COOH), hydroxyl (-OH), or carbonyl (-C═O) groups, respectively, using a chemical titration method. The results show that the -C═O groups could accelerate the nanozymatic catalysis kinetically, while the -OH ones were the catalytically inhibitive sites, which were further corroborated by the density functional theory (DFT) computations. The application potential of the WO3-x derivatives with an enhanced catalytic ability was verified via the colorimetric cholesterol sensing. The proposed method based on the benzoic anhydride (BA)-modified WO3-x QDs with deactivated -OH groups showed a wider linear range and higher sensitivity than those based on the unmodified ones.

Prescription drug disposal: Products available for home use

ObjectiveUnused medications in the home are often improperly stored and may lead to unintentional harm, misuse, and diversion. Single-use disposal systems products allow consumers to safely inactivate unused medication and provide an environmentally friendly alternative to flushing medication down the toilet or discarding in the trash. The objective of this commentary was to review current medication disposal options and inform pharmacists of new products that may be used by patients to dispose of medications in the home setting. Data sourcesCurrent recommendations on medication disposal from U.S. regulatory agencies (e.g., the Environmental Protection Agency) were reviewed and summarized comparatively. Information on the mechanism of action, price, and method of use of 8 new single-use disposal systems suitable for outpatient use were taken from each product manufacturer’s website. SummaryEight single-use disposal systems were identified. Seven products used chemical deactivation to render medication safe for disposal, and 1 product allowed consumers to mail medication to a central processing facility for incineration. Products ranged in size from 2 oz to 1 gal, offering consumers the ability to dispose of anywhere from 60 to 3000 tablets per unit, respectively. Unit costs varied widely from $5 per single-use pouch to $190 for a 40-gal box intended for incineration. ConclusionPharmacists and consumers must consider cost, effectiveness, and environmental impact when recommending and selecting products for medication disposal at home. More research is needed to understand the cost-effectiveness of each disposal system and to identify strategies to encourage uptake by health systems and use by consumers. Including content on home medication disposal in pharmacist–continuing education activities and raising workforce awareness of these products are critical to improving public safety.

Effects of alkali and alkaline earth metals on Cu-SSZ-39 catalyst for the selective catalytic reduction of NOx with NH3

Alkali/alkaline earth metals from urea solution and engine lubricating oil can induce the chemical deactivation of NH3-SCR catalysts. Cu-SSZ-39, with excellent catalytic performance and hydrothermal stability, is thought to be a good choice for the NOx abatement from diesel vehicles. In this work, the effects of alkali/alkaline earth metals on Cu-SSZ-39 were investigated for the first time. The deactivation effects of alkali/alkaline earth metals followed the order of K > Mg > Ca > Na. The surface area, isolated Cu2+ ions and acid sites greatly decreased after the introduction of alkali/alkaline earth metals. Na and K had greater influence on the zeolite surface acidity than Ca and Mg with the same loading amount (1 mmol per gram catalyst). The deterioration of the zeolite structure and the transformation of isolated Cu2+ ions to CuOx were observed after poisoning by each of the alkali/alkaline earth metals. The distribution of copper species is a very important factor determining the SCR performance of Cu-SSZ-39 after alkali/alkaline earth metals poisoning. This work provides a new insight into understanding deactivation mechanisms in Cu-based small-pore zeolites.