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New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce3+ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO2 from anatase to larger particles of rutile; and (iii)-the increase in PdO/Pd-ratio above its optimum. The modification by Ti of the La2O3-CeO2-Al2O3 system leads to higher resistance towards the presence of SO2 most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La2O3-CeO2-TiO2-Al2O3 catalyst follows the Mars-van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La2O3-CeO2-TiO2-Al2O3, supported on rolled aluminum-containing stainless steel (Aluchrom VDM®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model.

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Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) provide a reliable onboard way to control NOx emissions from glass-melting furnaces. The main limitation is the poisoning of this sensor by sulfur oxides (SOx) contained in the stream. To overcome this drawback, an "SO2 trap" with high SOx storage capacity and low affinity to NOx is required. Two CuO/BaO/SBA-15 traps with the same CuO loading (6.5 wt.%) and different BaO loadings (5 and 24.5 wt.%, respectively) were synthetized, thoroughly characterized and evaluated as SO2 traps. The results show that the 6.5%CuO/5%BaO/SBA-15 trap displays the highest SO2 adsorption capacity and can fully adsorb SO2 for a specific period of time, while additionally displaying a very low NO adsorption capacity. A suitable quantity of this material located upstream of the sensor could provide total protection of the NOx sensor against sulfur poisoning in glass-furnace exhausts.

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Sulfur poisoning and regeneration are global challenges for metal catalysts even at the ppm level. The sulfur poisoning of single-metal-site catalysts and their regeneration is worthy of further study. Herein, sulfur poisoning and self-recovery are first presented on an industrialized single-Rh-site catalyst (Rh1 /POPs). A decreased turnover frequency of Rh1 /POPs from 4317 h-1 to 318 h-1 was observed in a 1000 ppm H2 S co-feed for ethylene hydroformylation, but it self-recovered to 4527 h-1 after withdrawal of H2 S, whereas the rhodium nanoparticles demonstrated poor activity and self-recovery ability. H2 S reduced the charge density of the single Rh atom and lowered its Gibbs free energy with the formation of inactive (SH)Rh(CO)(PPh3 -frame)2 , which could be regenerated to active HRh(CO)(PPh3 -frame)2 after withdrawing H2 S. The mechanism and the sulfur-related structure-activity relationship were highlighted. This work provides an understanding of heterogeneous ethylene hydroformylation and sulfur-poisoned regeneration in the science of single-atom catalysts.

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AlNi pillared clay (AlNi-PILC) was synthesized firstly, and then MnO2 was supported via wetness impregnation from nitrate precursors. Sulphation was performed by in-situ decomposing ammonium sulfate with different concentrations over MnO2/AlNi-PILC. Catalysts before and after sulfur poisoning were characterized by XRD, N2 adsorption/desorption, HRTEM, XPS, H2-TPR and NH3-TPD. MnO2/AlNi-PILC exhibited high catalytic activity, allowing the complete toluene combustion. Structure of the catalyst was obviously damaged after sulfur poisoning. (001) crystal plane strength of AlNi-PILC was decreased significantly. Meanwhile, the specific surface area and pore volume reduced with increase of sulfate concentration. Sulfur species were readily formed on the surface of poisoned catalyst and deposited in the pore structure of AlNi-PILC, which resulted in significant impacts on the structural stability, acidity and the number of active species. These changes were responsible for the decreased catalytic performance.

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Recycling of deactivated palladium (Pd)-based catalysts can not only lower the economic cost of their industrial use but also save the cost for waste disposal. Considering that the sulfur-poisoned Pd (PdxSy) with a strong Pd-S bond is difficult to regenerate, here, we propose a direct reuse of such waste materials as an efficient catalyst for decontamination via Fenton-like processes. Among the PdxSy materials with different poisoning degrees, Pd4S stood out as the most active catalyst for peroxymonosulfate activation, exhibiting pollutant-degradation performance rivaling the Pd and Co2+ benchmarks. Moreover, the incorporated S atom was found to tune the surface electrostatic potentials and charge densities of the Pd active site, triggering a shift in catalytic pathway from surface-bound radicals to predominantly direct electron transfer pathway that favors a highly selective oxidation of phenols. The catalyst stability was also improved due to the formation of strong Pd-S bond that reduces corrosion. Our work paves a new way for upcycling of Pd-based industrial wastes and for guiding the development of advanced oxidation technologies toward higher sustainability.

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The activated coke is a promising support for catalysts, and it is important to study the performance of the activated coke catalyst on the removal of NOx. In the current research, a series of the activated coke-supported Mn-Cu catalysts are prepared by the incipient wetness impregnation method. The effects of the molar ration of Mn/Cu, the content of Mn-Cu, the calcination temperature, and reaction space velocity on NO conversion are investigated, and it was found that the 8 wt.% Mn0.7Cu0.3/AC had the best catalytic activity when the calcination temperature was 200 °C. The existence of SO2 caused the catalyst to deactivate, but the activity of the poisoning catalyst could be recovered by different regeneration methods. To uncover the underlying mechanism, BET, XPS, XRD, SEM and FTIR characterizations were performed. These results suggested that the specific surface area and total pore volume of the poisoning catalyst are recovered and the sulfite and sulfate on the surface of the poisoning catalysts are removed after water washing regeneration. More importantly, the water washing regeneration returns the value of Mn3+/Mn4+, Cu2+/Cu+, and Oα/Oß, related to the activity, basically back to the level of the fresh catalyst. Thus, the effect of water washing regeneration is better than thermal regeneration. These results could provide some helpful information for the design and development of the SCR catalysts.

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Hydrodechlorination is a promising technology for the remediation of water body contaminated with trichloroethylene (TCE). In this work, the liquid-phase hydrogenation of TCE by Raney Ni (R-Ni) and Pd/C under an open system have been studied, in which nascent H2 (Nas-H2) generated in situ from the cathode acted as a hydrogen source. Experimental results showed that TCE was completely eliminate from the solution through the synergistic effects of hydrodechlorination and air flotation due to the formation of continuous micro/nano-sized Nas-H2 bubbles from the cathode. Furthermore, the effects of inorganic anions and organic solvents on R-Ni and Pd/C hydrogenation activity were investigated, respectively. The results showed that NO3- and acetonitrile can form a competitive reaction with TCE; Sulfur with lone-pair electrons will cause irreversible poisoning to these two catalysts, and have a stronger inhibitory effect on Pd/C. This work helps to realize the separation of volatile halogenated compounds from water environment and provides certain data support for the choice of catalyst in the actual liquid-phase hydrogenation system.

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Low-medium temperature application of selective catalytic reduction (SCR) denitration in cement flue gas was established and investigated in this study. The 2000 h continuous operation shows the concentration of NOx at the outlet can be maintained at 24 mg/Nm3 on average, while due to the increase of SO2 in flue gas, the NOx concentration increased to 57.5 mg/Nm3 after long time operation. The sulfur deposition is the main reason for catalyst deactivation, and SO2 is still a big obstacle for low-medium temperature SCR application in cement flue gas. The denitration efficiency was tested as fluctuated from 73.5% to 86.2%, and ammonia concentration after SCR was as still as high as 22.5-60.0 mg/Nm3 due to the excessive ammonia injection from selective non-catalytic reduction (SNCR), shows serious ammonia escape problem for SNCR, and the potential application of hybrid SNCR-SCR technology. In order to maintain the denitration efficiency above 85.0%, the gaseous hourly space velocity (GHSV) should not be exceeded 2800 h-1, the electrostatic precipitators (ESP) setting at 60 kV was relatively appropriate, the temperature of the flue gas should be kept at above 200 °C. The concentrations and toxic equivalent quantities (TEQs) of the PCDD/Fs congeners in the flue gas raised greatly after SCR reactor, indicating the PCDD/Fs concentration should be concerned during the application of low-medium temperature SCR, especially for the waste co-disposal processes.

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The chemical design of new functional materials for solid oxide fuel cells (SOFCs) is of great interest as a means for overcoming the disadvantages of traditional materials. Redox stability, carbon deposition and sulfur poisoning of the anodes are positioned as the main processes that result in the degradation of SOFC performance. In this regard, double perovskite molybdates are possible alternatives to conventional Ni-based cermets. The present review provides the fundamental properties of four members: Sr2NiMoO6-δ, Sr2MgMoO6-δ, Sr2FeMoO6-δ and Sr2Fe1.5Mo0.5O6-δ. These properties vary greatly depending on the type and concentration of the 3d-element occupying the B-position of A2BB'O6. The main emphasis is devoted to: (i) the synthesis features of undoped double molybdates, (ii) their electrical conductivity and thermal behaviors in both oxidizing and reducing atmospheres, as well as (iii) their chemical compatibility with respect to other functional SOFC materials and components of gas atmospheres. The information provided can serve as the basis for the design of efficient fuel electrodes prepared from complex oxides with layered structures.

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While several proton-conducting anode materials have shown excellent tolerance to sulfur poisoning, the mechanism is still unclear due largely to the inability to probe miniscule amounts of sulfur-containing species using conventional surface characterization techniques. Here we present our findings in unraveling the mechanism of water-mediated sulfur tolerance of a proton conductor under operating conditions empowered by surface-sensitive, operando surface-enhanced Raman spectroscopy (SERS) coupled with impedance spectroscopy. Contrary to the conventional view that surface-adsorbed sulfur is removed mainly by oxygen anions, it is found that -SO4 groups on the surface of the proton conductor are converted to SO2 by a water-mediated process, as confirmed by operando SERS analysis and density functional theory (DFT)-based calculations. The combination of operando SERS performed on a model electrode and theoretical computation offers an effective approach to investigate into complex mechanisms of electrode processes in various electrochemical systems, providing information vital to achieve the rational design of better electrode materials.

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Sulfur poisoning has long been recognized as a bottleneck for the development of long-lived NH3-selective catalytic reduction (SCR) catalysts. Ammonium bisulfate (ABS) deposition on active sites is the major cause of sulfur poisoning at low temperatures, and activating ABS decomposition is regarded as the ultimate way to alleviate sulfur poisoning. In the present study, we reported an interesting finding that ABS decomposition can be simply tailored via adjusting the pore size of the material it deposited. We initiated this study from the preparation of mesoporous silica SBA-15 with uniform one-dimensional pore structure but different pore sizes, followed by ABS loading to investigate the effect. The results showed that ABS decomposition proceeded more easily on SBA-15 with larger pores, and the decomposition temperature declined as large as 40 °C with increasing pore size of SBA-15 from 4.8 to 11.8 nm. To further ascertain the real effect in NH3-SCR reaction, the Fe2O3/SBA-15 probe catalyst was prepared. It was found that the catalyst with larger mesopores exhibited much improved sulfur resistance, and quantitative analysis results obtained from Fourier transform infrared and ion chromatograph further proved that the deposited sulfates were greatly alleviated. The result of the present study demonstrates for the first time the vital role of pore size engineering in ABS decomposition and may open up new opportunities for designing NH3-SCR catalysts with excellent sulfur resistance.

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Continuous, in situ detection of hydrogen sulfide (H2S) in biological milieu is made possible with electrochemical methods, but direct amperometry is constrained by the generation of elemental sulfur as an oxidative byproduct. Deposition of a sulfur layer passivates the working electrode, reducing sensitivity and causing performance variability. Herein, we report on the use of a surface preconditioning procedure to deposit elemental sulfur on a glassy carbon electrode prior to measurement and evaluate performance with common analytical metrics. The lack of traditional anti-poisoning techniques (e.g. redox mediators, cleaning pulses) also allowed for facile surface modification with electropolymerized films. For the first time, a series of electropolymerized films were characterized for their H2S permselective behavior against common biological interferents. Highly selective, film-modified electrodes were then evaluated for their anti-biofouling ability in simulated wound fluid. The final optimized electrode was capable of measuring H2S with a low detection limit (i.e., <100 nM) and ∼80% of its initial sensitivity in proteinaceous media.

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Sulfur poisoning of V2O5/BaSO4-TiO2 (VBT), V2O5/WO3-TiO2 (VWT) and V2O5/BaSO4-WO3-TiO2 (VBWT) catalysts was performed in wet air at 350°C for 3hr, and activities for the selective catalytic reduction of NOx with NH3 were evaluated for 200-500°C. The VBT catalyst showed higher NOx conversions after sulfur poisoning than the other two catalysts. The introduction of barium sulfate contributed to strong acid sites for the as-received catalyst, and eliminated the redox cycle of active vanadium oxide to some extent, which resulted in a certain loss of activity. Readily decomposable sulfate species formed on VBT-S instead of inactive sulfates on VWT-S. These decomposable sulfates increased the number of strong acid sites significantly. Some sulfate species escaped during catalyst preparation and barium sulfate was reproduced during sulfur poisoning, which protects vanadia from sulfur oxide attachment to a great extent. Consequently, the VBT catalyst exhibited the best resistance to sulfur poisoning.

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The catalytic activities for benzene oxidation and resistance to SO2 poisoning were tested for a series of Pd/La-Cu-Co-O/cordierite catalysts, which were prepared using a multiple-step impregnation method. The XRD, SEM, and IR characterization techniques were performed to investigate the relationship between the catalytic performance and its physicochemical properties. When Pd/La-Cu-Co-O/cordierite catalysts with Pd loadings of 0.06 and 0.08 % were prepared at a calcination temperature of 500 °C for 5 h, they exhibited similar catalytic activity and sulfur resistance. When the concentration of benzene was 1500 ppm and the GHSV was 20000 h(-1), the benzene conversion was above 95 % at a reaction temperature of 350 °C in SO2 existing at 100 ppm. These results were mainly attributed to the cooperation between La-Cu-Co-O perovskite and the noble metal Pd. Specifically, the addition of copper can strengthen the catalytic activity of La-Co-O/cordierite catalysts by decreasing the crystalline size of the active ingredients. A moderate Pd addition can drastically improve the sulfur resistance and further improve the catalytic activity of the La-Cu-Co-O/cordierite catalyst.

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In order to study the sulfidation of a catalyst fixed bed, an in operando single pellet sensor was designed. A catalyst pellet from the fixed bed was electrically contacted and its electrical response was correlated with the catalyst behavior. For the sulfidation tests, a nickel catalyst was used and was sulfidized with H2S. This catalyst had a very low conductivity in the reduced state. During sulfidation, the conductivity of the catalyst increased by decades. A reaction from nickel to nickel sulfide occurred. This conductivity increase by decades during sulfidation had not been expected since both nickel and nickel sulfides behave metallic. Only by assuming a percolation phenomenon that originates from a volume increase of the nickel contacts when reacting to nickel sulfides, this effect can be explained. This assumption was supported by sulfidation tests with differently nickel loaded catalysts and it was quantitatively estimated by a general effective media theory. The single pellet sensor device for in operando investigation of sulfidation can be considered as a valuable tool to get further insights into catalysts under reaction conditions.

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Pd is more prone to sulfation compared to Pt. Given the chemical similarity between Pt and Pd, the radical divide in their tendencies for sulfation remains a puzzle. We explain this intriguing difference using an extensive first-principles thermodynamics analysis and computed bulk and surface phase diagrams. In practically relevant temperatures and O2 and SO3 partial pressures, we find that Pt and Pd show significantly different tendencies for oxidation and sulfation. PdO formation is favored even at low oxygen chemical potential; however, PtO2 formation is not favorable in catalytically relevant conditions. Similarly, PdSO4, and adsorbed SO3 and oxygen species on clean and oxidized surfaces are highly favored, whereas PtSO4 formation does not occur at typical temperature and pressure conditions. Finally, several descriptors are identified that correlate to heightened sulfation tendencies, such as the critical O chemical potential for bulk oxide and surface oxide formation, chemical potentials O and SO3 for bulk sulfate formation, and SO3 binding strength on metal surface-oxide layers, which can be used to explore promising sulfur resistant catalysts.

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Mono- and bimetallic Rh and Pt based NOx storage-reduction (NSR) catalysts, where the noble metals were deposited on the Al2O3 support or BaCO3 storage component, have been prepared using a twin flame spray pyrolysis setup. The catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. The NSR performance of the catalysts was investigated by fuel lean/rich cycling in the absence and presence of SO2 (25 ppm) as well as after H2 desulfation at 750 °C. The performance increased when Rh was located on BaCO3 enabling good catalyst regeneration during the fuel rich phase. Best performance was observed for bimetallic catalysts where the noble metals were separated, with Pt on Al2O3 and Rh on BaCO3. The Rh-containing catalysts generally showed much higher tolerance to SO2 during fuel rich conditions and lost only little activity during thermal aging at 750 °C.