Surface Sulfate Species Research Articles

In-situ characterization of dynamic Acidithiobacillus ferrooxidans-pyrite interaction via QCM-D-based method: Cell adhesion and biofilm formation in responding to surface sulfur speciation

Microbe-sulfide mineral interactions (MSMI), often manifested as biofilm formation, are ubiquitous in natural and engineered environments. Such interactions were much dependent upon the evolution of chemical species of mineral surface and microbial extracellular polymeric substances (EPS), and in-situ characterization of which have been a demanding and crucial task. In this study, quartz crystal microbalance with dissipation (QCM-D) was used to real time characterize the adhesion of Acidithiobacillus ferrooxidans onto the pyrite surface after introducing L-cysteine (an important component of EPS). And by combining with monitoring the EPS composition in biofilm by confocal laser scanning microscopy (CLSM) and the surface sulfur species by SEM-EDS and X-ray-photoelectron spectroscopy (XPS) as well as the changes in pH, ORP, [Fe2+] and [Fe3+] in solution during A. ferrooxidans-pyrite interaction, the results show that L-cysteine can lead to the Cys-S-S2Fe complex formation on pyrite surface, and under the dosage of 0.02 to 0.1 g/L of L-cysteine, the Cys-S-S2Fe complex promoted the cell adhesion and biofilm formation of A. ferrooxidans with secretion of more EPS proteins but less EPS glycoconjugates, resulting in the promotion of sulfur biooxidation with inhibition of iron biooxidation, corresponding to no obvious formation of jarosites. The higher dosage of L-cysteine (e.g., 0.2 g/L) inhibited biofilm formation, reduced iron/sulfur oxidation. These results deepen the understanding of the roles of L-cysteine on MSMI. This study demonstrates the QCM-D-based method can be widely used for in situ characterization of MSMI, and opens an alternative pathway for revealing the micro-mechanism of MSMI correlated to the macroscopic effects.

Selective Anchoring by Surface Sulfur Species Coupled with Rapid Interface Electron Transfer for Ultrahigh Capacity Extraction of Uranium from Seawater.

Improving the adsorption selectivity, enhancing the extraction capacity, and ensuring the structural stability of the adsorbent are the key to realize the high efficiency recovery of uranium. In this work, we utilized the strong Lewis acid-base interaction between S2- and U(VI)O22+ coupling rapid electron transfer at the MnS/U(VI)O22+ solid-liquid interface to achieve excellent selectivity, high adsorption capacity, and rapid extraction of uranium. The as-synthesized MnS adsorbent exhibited an ultrahigh uranium extraction capacity (2457.05 mg g-1) and a rapid rate constant (K = 9.11 × 10-4 g h-1 mg-1) in seawater with 100.7 ppm of UO2(NO3)2 electrolyte. The kinetic simulation reveals that this adsorption process is a chemical adsorption process and conforms to a pseudo-second-order kinetic model, indicating electron transfer at the MnS/U(VI)O22+ solid-liquid interface. The relevant (quasi) in situ spectroscopic characterization and theoretical calculation results further revealed that the outstanding uranium extraction property of MnS could be attributed to the highly selective UO22+ adsorption of MnS with lower adsorption energy as a result of the strong interaction between S2- and UO22+ and the rapid mass transfer and interface electron transfer from S2- and low-valent Mn(II) to U(VI)O22+.

Influences analysis of Sb/Si dopant in TiO2 on NH3-SCR activity and low temperature SO2 resistance of V2O5/TiO2 catalysts

The Sb/Si doped TiO2 prepared by sol–gel method were used as supports of V2O5/TiO2 SCR catalysts in order to improve SCR activity and SO2 resistance. The type of dopant atoms changed catalyst physiochemical properties discriminatively. Surface chemical properties of catalysts played more important role in their catalytic performance. Simultaneous enhanced surface acidity and redox capacity leaded to the better SCR activity for V2O5/Sb-TiO2 compared with other catalysts. The low temperature SO2 resistance was improved for the support doped catalysts. The special electronic charge migration brought by surface sulfate species for V2O5/Sb-TiO2 even elevated its SCR activity during SO2 resistance test, which was due to the formation of new acid sites and enhancement of redox performance. Even though NOx conversion for V2O5/Si-TiO2 decreased, the relative stable efficiency was kept at low temperatures with SO2. The results proved hetero atom doping in TiO2 by sol–gel method was a useful method to improve low temperature SO2 resistance of catalysts. By contrast, Sb is a better choice for the development of support doped V2O5/TiO2 SCR catalyst used in a wide temperature range.

Hydrophilic sulfurized nanoscale zero-valent iron for enhancing in situ biocatalytic denitrification: Mechanisms and long-term column studies

The aim of this study was to investigate the effects of hydrophilic sulfur-modified nanoscale zero-valent iron (S-nZVI) as a biocatalyst for denitrification. We found that the denitrifying bacteria Cupriavidus necator (C. necator) promoted Fe corrosion during biocatalytic denitrification, reducing surface passivation and sulfur species leaching from S-nZVI. As a result, S-nZVI exhibited a higher synergistic factor (fsyn = 2.43) for biocatalytic NO3- removal than nanoscale zero-valent iron (nZVI, fsyn = 0.65) at an initial nitrate concentration of 25 mg L−1-N. Based on kinetic profiles, SO42- was the preferred electron acceptor over NO3- when using C. necator and S-nZVI for biocatalytic denitrification. Up-flow column experiments demonstrated that biocatalytic denitrification using S-nZVI achieved a total nitrogen removal capacity of up to 2004 mg L−1 for 127 d. Notably, microbiome taxonomic profiling showed that the addition of S-nZVI to the groundwater promoted the growth of Geobacter, Desulfosporosinus, Streptomyces, and Simplicispira spp in the column experiments. Most of those microbes can reduce sulfate, promote denitrification, and match the batch kinetic profile obtained using C. necator. Our results not only discover the great potential of S-nZVI as a biocatalyst for enhancing denitrification via microbial activation but also provide a deep understanding of the complicated abiotic-biotic interaction.

Novel regenerated V- and Ce-mixed oxide modified catalysts for the NH3-SCR of NOx displaying a distinctive broad temperature window

The challenge for selective catalytic reduction (SCR) of NOx with NH3 is to improve de-NOx activity at low temperatures while simultaneously improving the tolerance of catalysts towards SO2 poisoning. Herein, V and Ce oxides were loaded on deactivated SCR catalysts subjected to acid pickling (CAT) via impregnation to recover de-NOx activity. The resulting V–Ce@CAT catalyst exhibited 85–95% NOx conversions over a wide temperature window of 200–450 °C while conversions of only 40–78% over the same temperature range were observed with CAT (spent catalyst treated with acid). Interestingly, in addition to the high tolerance towards SO2 displayed by V–Ce@CAT, the catalyst exhibited improved reactivity after the introduction of 200 ppm SO2, with the NOx conversion increasing from 80% to 87%. The results indicated that a kinetic equilibrium was reached between the formation and decomposition rates of Ce2(SO4)3 on V–Ce@CAT which prevented the accumulation of surface sulfate species, thereby protecting the main active species V from catalytic inactivation. Furthermore, in situ DRIFTS revealed that the NH3-SCR reaction pathway of V–Ce@CAT follows the L-H mechanism.

Effect of morphology and simultaneous sulfation on Fe doped CeO2 for selective catalytic reduction of NOx with NH3

Researchers have been developing novel environment-friendly NH3-SCR catalysts for controlling NOx emission from fossil fuel combustion. Fe doped CeO2 catalysts with nanorod, nanocube and nanopolyhedron shape were synthesized and sulfation was conducted on porous nanorod simultaneously. Their NOx conversions were in sequence of sulfated porous nanorod (S-FeCeOx) > nanorod (R-FeCeOx) > nanopolyhedron (P-FeCeOx) > nanocube (C-FeCeOx) and presented distinct morphology dependence. S-FeCeOx catalyst possessed above 95 % NOx conversion and nearly 100 % N2 selectivity in very high gas hourly space velocity of 240, 000 mL·g−1·h−1 at 275–400 °C. The sequence of BET specific surface area was: P-FeCeOx > R-FeCeOx > S-FeCeOx > C-FeCeOx and thus the change of physical adsorption capacity may be not the main reason for high SCR catalytic activity of S-FeCeOx and R-FeCeOx. Fe doping and sulfation induced porous nanorod shape with preferentially exposed {110} faces, most oxygen vacancy defect sites and highest surface chemisorbed oxygen ratio, which contributed to the highest NOx conversion of S-FeCeOx. Fe doping mainly increased strong acid sites, and surface sulfate species significantly increased Brønsted acid sites promoting NH3 adsorption and suppressed NOx adsorption on S-FeCeOx catalyst, beneficial to both high NOx conversion and low N2O formation on it. R-FeCeOx catalyst mainly followed Langmuir-Hinshelwood mechanism, while SCR reaction mechanism was changed by sulfation and S-FeCeOx catalyst mainly followed Eley-Rideal mechanism.

Performance enhancement of elemental mercury removal from syngas over Fe7SC sorbent: Experimental and theoretical studies

In this study, a Fe7SC sorbent was prepared via hydrothermal impregnation and used to eliminate Hg0 from simulated syngas. A certain amount of oxygen was introduced to induce targeted H2S oxidation to form active surface sulfur species for the enhanced capture of Hg0 over Fe7SC. The effects of the introduced oxygen, temperature, and syngas composition (H2S, CO, H2, and H2O) on Hg0 adsorption performance were investigated. X-ray photoelectron spectroscopy, Hg0-temperature programmed desorption, and density functional theory calculations were performed to elucidate the Hg0 removal mechanism. Fe7SC exhibited a superior Hg0 removal performance (approximately 99.2%) in the presence of H2S + O2 at 150 °C. The interaction between H2S and the introduced oxygen was responsible for its superior Hg0 capture capacity. CO and H2 suppressed Hg0 adsorption, and H2O inhibited Hg0 removal owing to competitive adsorption. Results of the Bangham kinetic analysis indicate that Hg0 surface chemisorption is the primary rate-controlling step. Hg0 adsorption on the Fe7SC sorbent may follow the Eley–Rideal mechanism, in which the active sulfur species generated from H2S oxidation react with gaseous Hg0 to form HgS.

Experimental and theoretical analysis of elemental mercury removal from syngas over Fe-Ti spinel

A magnetic Fe-Ti spinel sorbent was synthesized by the co-precipitation method and applied to remove gaseous Hg0 from syngas. A superior Hg0 removal performance was achieved in the temperature range of 120–180 °C, and the highest an average removal efficiency of was approximately 95% at 150 °C under simulated syngas. H2S was adsorbed on the Fe-Ti spinel surface，which generated active sulfur species, and enhanced the Hg0 removal efficiency significantly. CO, H2 and H2O variably suppressed the Hg0 removal performance. H2S-pretreatment, X-ray photoelectron spectroscopy (XPS) and Hg0-temperature programmed desorption (Hg0-TPD) results demonstrated that Hg0 reacted with H2S over Fe-Ti spinel followed the Eley-Rideal mechanism, in which gas-phase Hg0 reacted with the active surface sulfur species generated from H2S oxidation and formed surface-bonded HgS. The surface Fe3+ and surface-active oxygen species were involved in the H2S and Hg0 adsorption and transformation process. Stability and regeneration cycling experiments indicated that Fe-Ti spinel exhibited excellent stability for Hg removal and great regeneration ability. Density functional theory (DFT) calculations showed that H2S underwent strong chemisorption on the Fe-Ti spinel surface with an adsorption energy of −116.988 kJ/mol, and then H2S further dissociated on the sorbent surface to generate active sulfur species, which reacted strongly with gas-phase Hg0 to form HgS.

SO2-Tolerant Catalytic Reduction of NOx via Tailoring Electron Transfer between Surface Iron Sulfate and Subsurface Ceria.

Currently, SO2-induced catalyst deactivation from the sulfation of active sites turns to be an intractable issue for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. Herein, SO2-tolerant NOx reduction has been originally demonstrated via tailoring the electron transfer between surface iron sulfate and subsurface ceria. Engineered from the atomic layer deposition followed by the pre-sulfation method, the structure of surface iron sulfate and subsurface ceria was successfully constructed on CeO2/TiO2 catalysts, which delivered improved SO2 resistance for NOx reduction at 250 °C. It was demonstrated that the surface iron sulfate inhibited the sulfation of subsurface Ce species, while the electron transfer from the surface Fe species to the subsurface Ce species was well retained. Such an innovative structure of surface iron sulfate and subsurface ceria notably improved the reactivity of NHx species, thus endowing the catalysts with a high NOx reaction efficiency in the presence of SO2. This work unraveled the specific structure effect of surface iron sulfate and subsurface ceria on SO2-toleant NOx reduction and supplied a new point to design SO2-tolerant catalysts by modulating the unique electron transfer between surface sulfate species and subsurface oxides.

Cu- and Ce-promoted nano-heterostructures on vanadate catalysts for low-temperature NH3–SCR activity with improved SO2 and water resistance

The objective of this study was to demonstrate a facile strategy for vanadate-based catalysts having high NOx conversion efficiency (∼96% @ 220 °C) and improved SO2 resistance by impregnating highly-dispersed CuO–CeO2 nano-heterostructures to V2O5–CeO2–WO3/TiO2 catalysts. The key design of catalysts was based on the maximization of interface chemistry towards synergetic effects of catalytic and redox reactions between Cu and Ce species. The impregnation of 0.1 wt% CuO–CeO2 possessed more surface acid sites and enhanced redox ability at low temperatures (180–220 °C). Based on Gibbs energy calculation and XPS results, thermodynamically favorable reaction of Cu2+ + Ce3+ → Cu+ + Ce4+ made it a perfect candidate for an excellent redox system with V4+/V5+ charge imbalance proportion through electron migration at the adjacent interface. The strong redox interaction and facile electron transfer could also restrain the formation of surface sulfate species and showed an excellent SO2 and water tolerance.

Synthesis of Al-incorporated sulfated zirconia with improved and stabilized surface sulfur species for removal of trace olefins from aromatics

Incorporating Al into zirconia significantly improves and stabilizes the surface sulfur species. The outstanding catalytic performance of Al-incorporated sulfated zirconia was obtained when it was applied in removing trace olefins from aromatics.

Morphology and Catalytic Performance of MoS2 Hydrothermally Synthesized at Various pH Values

Although preparation conditions are known to affect the morphology and catalytic performance of hydrothermally synthesized MoS2, the influence of pH remains unclear. Herein, unsupported MoS2 was prepared from ammonium tetrathiomolybdate (ATTM) by a hydrothermal reaction at various pH values under a reaction pressure of 2 MPa. The physical and chemical properties of the MoS2 samples were characterized, and the catalytic performance for CO methanation was examined. With increasing pH, the morphology of the MoS2 particles transformed from aggregates of irregular grain-like particles to flower-like particles through the agglomeration of fine mesoporous nanoflakes. Hydrothermal synthesis at a pH of 9.5 increased the MoS2 crystallinity by enhancing the stacking of the (0 0 2) lattice plane. The MoS2 samples prepared at pH 7.0 and 9.5 showed increased CO conversion during methanation, which was associated with a low concentration of Mo5+ species and the presence of surface sulfate species. Thus, a high pH during catalyst preparation may promote the complete decomposition of ATTM to MoS2 and the formation of sulfur vacancies, which can facilitate methanation.

Unraveling SO2-tolerant mechanism over Fe2(SO4)3/TiO2 catalysts for NOx reduction

Developing low-temperature SO2-tolerant catalysts for the selective catalytic reduction of NOx is still a challenging task. The sulfation of active metal oxides and deposition of ammonium bisulfate deactivate catalysts, due to the difficult decomposition of the as-formed sulfate species at low temperatures (<300 °C). In recent years, metal sulfate catalysts have attracted increasing attention owing to their good catalytic activity and strong SO2 tolerance at higher temperatures (>300°C); however, the SO2-tolerant mechanism of metal sulfate catalysts is still ambiguous. In this study, Fe2(SO4)3/TiO2 and Ce2(SO4)3/TiO2 catalysts were prepared using the corresponding metal sulfate salt as the precursor. These catalysts were tested for their low-temperature activity and SO2 tolerance activity. Compared to Ce2(SO4)3/TiO2, Fe2(SO4)3/TiO2 showed significantly better low-temperature activity and SO2 tolerance. It was demonstrated that less surface sulfate species formed on Fe2(SO4)3/TiO2 and Ce2(SO4)3/TiO2. However, the presence of NO and O2 could assist the decomposition of NH4HSO4 over Fe2(SO4)3/TiO2 at a lower temperature, endowing Fe2(SO4)3/TiO2 with better low-temperature SO2 tolerance than Ce2(SO4)3/TiO2. This study unraveled the SO2-tolerant mechanism of Fe2(SO4)3/TiO2 at lower temperatures (<300 °C), and a potential strategy is proposed for improving the low-temperature SO2-tolerance of catalysts with Fe2(SO4)3 as the main active component or functional promoter.

Cerium oxide-sulfur nanohybrids: Combining the robust adsorption of polysulfides with enhanced redox kinetics to improve the energy Storage capabilities of Li-S batteries

An in-depth investigation of the physical and chemical parameters that affect Li-sulfur batteries is imperative to optimize their performances. Here, we report promising [CeO2]100-x-[S8]x nanohybrids for anchoring lithium polysulfides (LiPSs) that are generated during cycling. The composition of [CeO2]100- x-[S8]x (x = 30, 50 and 70%) could be simply controlled by varying the CeO2/S8 mass ratio added in each reaction. Our results indicated that the [CeO2]100- x-[S8]x nanohybrids displayed a crystalline structure composed of both phases (CeO2 and S8), indicating an efficient impregnation process of S8 on the CeO2 nanowire surface. The surface area of CeO2 nanowires decreased as the amount of S8 was increased, and the [CeO2]70-[S8]30 nanohybrid maintained a uniform distribution of S8 over the entire CeO2 nanowires. Remarkably, the [CeO2]70-[S8]30 nanohybrid showed the best Li-storage performance, leading to specific capacities of approximately 600 mA h g–1 over 160 cycles and a Coulombic efficiency of approximately 100%. Moreover, this sample showed excellent rate capability performance (even discharging at 10 A g–1). Additionally, the chemical interaction of CeO2 with LiPS was demonstrated by a visual experiment through the addition of pure CeO2 in a solution of Li2S6. The solution containing CeO2 nanowires became completely colorless after 30 min. To further investigate these improvements, density functional theory (DFT) calculations revealed the formation of strong interactions between the CeO2 nanowire surface and different sulfur species. For instance, the adsorption energies between the CeO2 nanowires and S8, Li2S4, and Li4S8 were –3.95, –5.84 and –7.31 eV, respectively, suggesting that the [CeO2]70-[S8]30 nanohybrid provided an appropriate surface to anchor LiPS by electrostatic interactions, leading to faster redox kinetics in Li-sulfur battery applications.

Photoluminescence investigations of sulfur quantum dots synthesized by a bubbling-assisted strategy.

Sulfur quantum dots (S-dots) emerge as promising luminescent materials owing to their remarkable optical properties. However, the mechanisms of their formation and photoluminescence remain concealed. We reveal these mechanisms by the bubbling-assisted synthesis and spectroscopic study of S-dots formed from sulfur ions produced by the alkaline oxidation of bulk sulfur under the passivation of PEG. The emission colour of the S-dots depends on the size, explained by the quantum confinement effect. The dots' luminescent quantum efficiency is strongly affected by the surface sulfur species, which is optimized by the proper surface oxidation. The simple synthesis, excellent luminescence properties, and metal-free nature attract S-dots to optoelectronic and electroluminescence applications.

Minutes periodic wet chemistry engineering to turn bulk Co-Ni foam into hydroxide based nanosheets for efficient water decomposition

Herein, in order to promote the scaled-up manufacturing of efficient nanostructured electrocatalysts, we pioneer a novel ultrafast wet chemistry engineering to turn bulk Co-Ni foam into S activated hydroxide based nanosheets (CoNi-OH|S), with short period less than six minutes. The uniform nanosheets morphology is in-situ formed through designed nitro-hydrochloric acid enhanced corrosion within 30 s, then the nanosheets are naturally oxidized to CoOOH/Ni(OH)2 (CoNi-OH) when drying in the air. To fully boost the electrochemical activities, S activation is conducted through facile chemical bath in S anion-rich aqueous solution with five minutes. The as formed surface sulfur species could optimize the protons adsorption, thus benefitting the HER electrocatalysis. Besides, the Co3+ sites with low coordination are also increased by S activation, which could facilitate the de-protonation of OOH, thus promoting the OER electrocatalysis. Finally, such ultrafast surface engineering derived CoNi-OH|S electrodes afford the relatively low overpotentials of 167 mV for HER and 270 mV for OER at 10 mA cm−2. This wet chemistry strategy further ensures that the large area self-supported electrodes can be easily prepared within several minutes, which would inspire the large-scale synthesis and practical application of similar electrocatalysts in this field.

Characterization of Sulfated SnO2-ZrO2 Catalysts and Their Catalytic Performance on the Tert-Butylation of Phenol

Understanding the catalytic behavior of sulfated metal oxides has been the topic of several research studies in the past few decades. Their apparent super-acidic behavior has been correlated with the molecular structure of the surface sulfate species. Herein, we couple FTIR and Raman spectroscopies to study the molecular structural evolution of surface sulfate species on mixed metal hydroxides as well as calcined oxides. We show that on the surface of hydroxides, monodentate and possibly bidentate species are dominant, while for SnO2-rich samples, clusters of polymeric sulfate species may also be present. After calcination, sulfate species bind strongly on the surface of mixed oxides, and different configurations can be seen with a range of S=O functionalities of varying strength. Through comparison of the catalytic performance of all sulfate oxides in the tert-butylation of phenol, it was found that SnO2-rich samples show high TBA conversion, with monoalkylated phenols as the primary product.

Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO2 resistant NH3-SCR catalysts for NO removal

A series of ceria-zirconia solid solutions (CexZr1-xO2) were prepared by co-precipitation method and then sulfated with SO2 + O2 at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH3 (NH3-SCR) showed that the activity of the sulfated CexZr1-xO2 catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated Ce0.6Zr0.4O2 catalyst showed the most desirable NH3-SCR activity at 250-300 °C, and exhibited much better SO2 resistance at 250 °C. Detailed characterization results demonstrated that Ce0.6Zr0.4O2 could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO2 at 200 °C. After sulfation treatment, more Ce3+ and oxygen vacancies were formed on the surface of Ce0.6Zr0.4O2. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared Ce0.6Zr0.4O2, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated Ce0.6Zr0.4O2 had more reactive acid sites to participate in the NH3-SCR and the reaction proceeded via Eley-Rideal mechanism. This work proved that sulfation treatment could be used in designing an efficient cerium-zirconium based NH3-SCR catalyst with great application prospect.

Laponite immobilized TiO2 catalysts for photocatalytic degradation of phenols

Laponite immobilized titania catalysts were prepared by a pillaring process and by hydrothermal synthesis (HT) applying different titania sources such as TiCl4 and TiOSO4. Textural investigations (XRD, TEM, N2 physisorption) evidenced that by the pillaring procedure a high specific surface area (∼450 m2 g−1) mesoporous composite with 5–6 nm sized anatase nanoparticles were formed retaining the morphology of parent laponite structure. In contrast, by hydrothermal treatment with titanium oxysulfate the initial laponite structure was destroyed and a more opened nanoporous silica/titania material was formed with bigger, about 14 nm anatase particles.FT-IR spectroscopic investigations revealed the different acidic character of titania/Laponite composite samples showing stronger Lewis and weak Brönsted acid sites on both catalysts. However, acidic centers in titania pillared laponite stem from Ti–O–Si bonds, whereas in HT sample from the separated, ionic, surface sulfate species on titania.Catalytic activity of titania/Laponite composites were tested in photo-oxidation of model 10–5 M phenol and 2,4,6-trichlorophenol (TCP) water solutions. Catalytic tests were carried out in a home constructed batch-type photo-reactor with oxygen bubbling, and applying commercial low pressure Hg lamps emitting UV-light at 254 nm and 361 nm. Catalytic results showed that utilization of titania/Laponite catalysts enhanced the photo-oxidation activity. Hydrothermally prepared sample showed much better catalytic performance than titanium chloride pillared one, probably due to the bigger titania particles and the more opened mesoporous structure of titania/Laponite HT, and moreover to the peculiar surface acidic properties of sulfated titania species. Separation of catalysts from reaction media even in tap water was much easier than that of commercial titania, i.e. by self-settling.

New Insights into the Decomposition Behavior of NH4HSO4 on the SiO2-Decorated SCR Catalyst and Its Enhanced SO2-Resistant Ability.

This article illustrates the detailed decomposition behavior of NH4HSO4 on the TiO2 and TiO2–SiO2 supports, along with the effect of SiO2 addition on the sulfur resistance of the corresponding V2O5-based catalysts. For TiO2 support, sulfate species selectively occupied its surface basic hydroxyl groups, while Si–OH groups functioned as the main sites for the accommodation of NH4HSO4 over the TiO2–SiO2 mixed support, enabling its surface sulfate species with higher thermal stability. Compared with NH4+ on the TiO2 surface, NH4+ on the TiO2–SiO2 mixed support was much easier to be consumed during the heating process, hence causing some variations in the decomposition behavior of NH4HSO4. Finally, adding SiO2 enhanced the SO2 tolerance properties of the catalysts to a certain extent. When exposed to the SO2-containing flue gas, the deposition of NH4HSO4 mainly caused serious deactivation of SiO2-free catalyst, while the as-accumulated SO42– also contributed to the declined activity of SiO2-added catalyst. These results ensured the potential commercialization of TiO2–SiO2-based catalysts in the typical low-temperature selective catalytic reduction systems in the short run and pointed out a strategy to design new catalysts with superior activity and enhanced SO2-tolerant ability.