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H2O resistance of a catalyst is often underrated in reducing wet NOX and forming/pyrolyzing ammonium (bi)sulfate (AS/ABS) poisons, yet, is improved markedly when Ni1V2O6 and Sb2O5 serve as a prime activator and a promoter, respectively.

The role of SiO2 and WO3 in CeVO4-based catalyst supported on TiO2 support containing silica-tungsten was systematically investigated for selective catalytic reduction (SCR) by hydrothermal aging. It has been found that the CeVO4 with SiO2 and WO3 added to TiO2 (i.e., CeVO4/TWS) is the optimal catalyst to promote N2 selectivity through improved thermal stability and NH3 oxidation. CeVO4/TWS(HT; hydrothermal aging) had abundant defects and surface adsorbed oxygen species even after thermal aging. The high Vn+ (n = 4, 3) fraction of CeVO4/TWS(HT) is due to the improved thermal stability by adding SiO2 and WO3 to TiO2. The addition of SiO2 and WO3 maintains NH3 adsorption and redox properties, so the TWS support exhibits high thermal stability. As the NH3-SCR reaction mechanism, the pristine catalyst shows an Eley–Rideal and Langmuir–Hinshelwood models as dual model (ER-LH) based on abundant Lewis and Bronsted acid sites below 300 °C. On the other hand, the hydrothermal aged catalyst dominates the Eley–Rideal mechanism (reaction of activated ammonia with gaseous NO) based on Lewis acid sites. This study comprehensively shows that CeVO4-based catalysts have improved thermal stability by including SiO2 and WO3 in the TiO2 support.

Rare-earth metal vanadates (RMVO4) typically possess an iso-structural tetragonal architecture but vary in terms of their Lewis acidic (LA) properties, which depend on the nature of the RM element. This study pioneers the exploitation of the LA sites inherent to RMVO4 on a TiO2 support as grafting points to immobilize HSOA−/SOA2−/H3−BPO4B− species, which are notorious poisons of LA sites during the selective catalytic reduction of NOx with NH3 (SCR). The HSOA−/SOA2− (S) and H3−BPO4B− (P) species served as Bronsted acidic (BA) sites with distinct distributions and modulated the redox cycling characteristics of the resulting RM-S/RM-P catalysts. The SCR performance of Ce-S/Ce-P and the other catalysts was dictated by the redox sites and amount of BA sites, respectively, at ≤300–340 °C, while exhibiting ‘M’-shaped periodicity in a plot of SCR performance versus the type of RM. This periodicity was maintained at ≥300–340 °C, although the catalyst performance was primarily dictated by the redox sites. With the exception of Ce-S/Ce-P, the RM-P catalysts outperformed the corresponding RM-S analogues in accelerating the SCR at ≤300–340 °C, whereas the opposite trend was observed at ≥300–340 °C. Furthermore, Gd-S consumed NOx and NH3via diverse pathways of NH4NO3 formation/transformation other than the SCR and production of ammonium sulfate (AS)/ammonium bisulfate (ABS) poisons, thus tolerating AS/ABS poisons in the most efficient manner at 250 °C. This study demonstrates the importance of the RM in HSOA−/SOA2−/H3−BPO4B−-modified RMVO4 frameworks, whose properties on the BA and redox site and SCR performance varied markedly with the choice of RM.

The roles of WO3 and SiO2 in Ce-V catalysts supported on TiO2 comprised tungsten-silica were investigated systematically for NH3-SCR (selective catalytic reduction) and NH3-oxidation at high temperatures. When SiO2 and WO3 were added to TiO2, the surface area of Ce-V/TWS was maximized and the formation of Ti O Si bond reduced nanoparticle size compared to without SiO2. The Ce-V/TWS surface had greater abundance of catalytic defects and surface oxygen species via XPS results. Increasing the (V4+ + V3+) fraction increased the catalytic activity, which is attributed to the enhanced SCR performance at a wide temperature range due to the addition of WO3 and SiO2 to TiO2. The catalysts using the TWS supports exhibit high catalytic activity, since WO3 and SiO2 can promote redox properties. It was shown that Ce-V/TWS was the most suitable catalyst for selectively producing N2 via thermodynamically unavoidable NH3 direct oxidation as the temperature increased. In addition, hydrothermal aging effects were investigated for the Ce-V/TWS catalyst prepared by TiO2 supports including WO3 and SiO2 (comparison with vanadium-tungsten/titania). This study demonstrates the feasibility of utilizing WO3 and SiO2 in the TiO2 support as a possible way to increase catalytic activity and N2 selectivity in NH3-SCR at high temperatures.

Mn oxide is a particular class of metal phase highly active in reducing NOX or oxidizing NH3 at low temperatures yet needs amendment in terms of surface acidic/redox sites to improve selectivities ...

Catalytic rare earth metal vanadates have shown promise for efficiently converting NOX to N2 at elevated temperatures (NH3-SCR) (e.g., CeVO4, ErVO4, and TbVO4). However, these vanadates have limitations as catalytic sites because of three major issues such as weak hydro-thermal stability, low N2 selectivity, and limited numbers of major active (Lewis acid) sites. As an efficient way to circumvent these constraints, this study showcases a means of structurally modifying vanadate with additional rare earth metals to generate bimetallic vanadates with variable metal compositions. While selecting Ce and Er as metal constituents, a series of Ce1-XErXVO4 solid solutions were deposited onto WO3-promoted TiO2 supports (WO3-TiO2) to form ErX catalysts, whereas a control simulating a commercial catalyst (V) was also synthesized using WO3-TiO2 for comparison. Bimetallic Ce1-XErXVO4 (X = 0.25, 0.5, and 0.75) showed enhanced redox features, improved the quantities of Lewis/Bronsted acid sites and defects, and increased resistance to hydro-thermal aging relative to their monometallic analogues (X = 0 and 1). The optimal Er composition of Ce1-XErXVO4 studied was found to be X = 0.5. This was because Er0.5 provided the best redox character, the largest number of active sites with the desired Lewis acid strength, and the greatest hydro-thermal stability among all the ErX and V catalysts studied. This led to the best catalytic consequence of Er0.5 in the selective NH3 oxidation and the NH3-SCR reactions, both of which should achieve high N2 productivities at elevated temperatures. In addition, Er0.5 subjected to hydro-thermal aging also extended its best NH3-SCR performance among all aged catalysts studied even to low temperature regime of

The influence of molybdenum on the selective catalytic reduction (SCR) performance and SO2 durability of V/Mo-Ti catalysts was investigated. The characteristics of the catalysts were investigated by Brunauer-Emmett-Teller (BET) surface area analysis, field-emission transmission electron microscopy (FE-TEM), Raman spectroscopy, NH3-temperature programmed desorption (NH3-TPD), in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTs), SO2 temperature-programmed desorption (SO2-TPD), and X-ray photoelectron spectroscopy (XPS). The V/Mo-Ti catalysts exhibited improved SCR performances and SO2 resistances at 250 °C compared to those of V/W/Ti catalysts. The improved catalytic activity was shown to be imparted by amorphous MoOx. The formation of amorphous MoOx species with the addition of molybdenum to titanic acid was found to be more significant than that by the addition of molybdenum to crystalline TiO2. The increased density of NH3-adsorption and Bronsted-acid sites by addition of molybdenum was found to have a positive effect on catalyst performance. Since the reaction between SO2 and VOx was suppressed by the addition of molybdenum, the area of the SO2-TPD peak due to desorption of adsorbed SO2 from the catalyst surface was reduced. This decrease in the amount of adsorbed SO2 improved the SO2 resistances of the catalysts. The V/Mo-Ti catalysts exhibited increasing activities and SO2 resistances with increasing Mo6+ ratio (and Mo6+ atoms/cm3). Furthermore, they exhibited suppressed formation of ammonium sulfate salts due to decreased SO2 adsorption, as the reaction of terminal V O groups and adsorbed SO2 is inhibited by the addition of molybdenum. Thus, the V/Mo-Ti catalysts exhibited better catalytic activities and SO2 durability than those of V/W/Ti catalysts.

Investigation of cerium sulfate species on sulfated SbVCT (Sb/V/Ce/Ti) catalysts at various temperatures was carried out by diffused-reflectance infrared Fourier-transform spectroscopy (DRIFTs) analysis. The catalyst sulfated at a high temperature, SbVCT (500s-1) (i.e., sulfated at 500 °C), exhibited higher NOx removal performance at low temperatures than the SbVCT (fresh) and VWTi catalysts. The in-situ DRIFTs results showed that the ionic character of SbVCT (500s-1) increased significantly, whereas SbVCT (250s-1) only had covalent character. For SbVCT (250s-1), a small amount of surface cerium sulfate species was formed. With increasing sulfation temperature, more cerium sulfate species formed as a bulk-like species, and its rate of formation increased. Bulk-like cerium sulfate species formed at high temperatures do not change upon exposure to low temperatures. However, surface cerium sulfate species formed at low temperatures underwent phase change to bulk-like species upon exposure to high temperatures. Catalysts containing bulk-like cerium sulfate species exhibit high SCR performance at low temperatures. Therefore, the SCR performance improved when the SbVCT (250s-1) was exposed to high temperatures. A related model has been proposed to understand how the interactions of sulfate species of SbVCT are affected by sulfation temperature. Furthermore, the SO2 resistance of SbVCT was superior to that of the VWTi catalyst because it delayed the adsorption of SO2 onto the catalytic surface. Through functionalization of cerium sulfate species, SbVCT can exhibit improved low-temperature activity and durability.

SO2 is notorious to poison the catalytic surface during the selective catalytic reduction of NOX with NH3 (NH3-SCR). Nonetheless, the use of poisonous SO2 and O2 as surface modifiers to generate the surface metal-SOY2− species (Y = 3 or 4) can be one of the viable ways for promoting catalytic NH3-SCR consequence. To develop a novel catalyst that is highly active in and selective to NH3-SCR, we previously explored four catalytic copper vanadates and determined the optimum active phase (i.e., Cu3V2O8, denoted as Cu3) that revealed the greatest NH3-SCR performance, when combining with a proper Sb quantity of 1.4 wt. %. While using anatase (TiO2) as a support, this study investigated the effect of SOY2− functionalization temperature on the surface property of the optimum catalyst, Sb-promoted Cu3V2O8 on TiO2 (Cu3-Sb1.4/TiO2). Cu3-Sb1.4/TiO2 was subjected to SOY2− functionalization at 300, 400, and 500 °C, leading to the formation of S300, S400, and S500. Although the catalyst surface was not fully functionalized with the SOY2− species in S300-S500, various metal sulfate or sulfite species appeared on the surfaces and showed distinct surface features. The SOY2− functionalization of Cu3-Sb1.4/TiO2 could not increase the quantity of Lewis acid sites. However, 400 °C was deemed as an adequate SOY2− functionalization temperature for increasing the quantity of Brӧnsted acid sites and the redox behavior of the intact Cu3-Sb1.4/TiO2. This could result from the increase in the surface abundance of Cu(SO4) or from a proper combination of the metal-bound SOY2− species with mono-dentate and bi-dentate binding configurations. Apart from exhibiting moderate tolerance to hydrothermal aging, S400 was also validated to improve its resistance to alkali-metal, H2O, SO2, (NH4)2SO4, or (NH4)HSO4 in comparison to its SOY2−-unfunctionalized counterpart, S300, and S500.

TiO

Catalysts are severely poisoned by ammonium sulfate (AS) and ammonium bisulfate (ABS) during selective catalytic NO

The effect of adding Mo and/or Sb to a VTi catalyst on its activity and durability in the selective catalytic reduction (SCR) of nitrogen oxide by NH3 was investigated. The addition of an appropriate amount of Mo–Sb significantly improved the catalyst specific surface area, enhanced the number of Bronsted acid sites, and adjusted the surface species composition. The catalytic activity improved as the Vn+ (n = 4, 3) fraction increased due to the formation of functional groups on the catalyst surface. The redox properties, amount of active labile oxygen, and number of surface oxygen vacancies were improved by the presence of V2MoO8. This species also played an important role in improving the SCR performance and water/sulfur durability of the catalysts due to its sufficient acidity enhancement and reduction of SO2 adsorption. The addition of Mo–Sb likely enhanced catalyst SO2 durability because it reduced SO2 adsorption by inhibiting the reaction between terminal oxygen (V = O) and SO2(g).

A way to fulfill efficient exploitation of desired catalytic nature provided by V oxide is to modify its chemical structure through the incorporation of secondary transition metal species. This paper reports the use of Cu as a modifier of high-valent V oxide (V2O5) to produce a class of copper vanadates and their utilization as active sites for the selective catalytic reduction of NOX (X = 1 or 2) by NH3 (NH3-SCR). All catalysts contained ∼2 nm-sized copper vanadate particles highly dispersed on anatase with desired vanadate phases. The anatase-supported Cu5V2O10 provided a greater quantity of acid sites with improved redox character than Cu1V2O6, Cu2V2O7, and Cu3V2O8, thereby exhibiting the greatest NH3-SCR performance under ideal reaction conditions. Anatase-supported Cu3V2O8, however, was found to possess the most preferred surface properties among the catalysts post sulfation. This was evidenced by NH3-SCR runs of the catalysts under reaction conditions with H2O and SO2-including stream, where all catalysts were pre-sulfated by SO2 and O2 at elevated temperatures. The NH3-SCR performance of the optimum Cu3V2O8 on anatase was further promoted after sulfation of the catalyst with the optimum content of Sb promoter. The Sb promoter was verified to enhance the redox feature and minimize the interactions among catalyst surfaces and SO2/ammonium (bi)sulfates during the NH3-SCR, as evidenced by durability experiments. While showing N2 selectivities as ∼100% at ≤ 400 °C, the optimized Sb-promoted Cu3V2O8 on anatase showed high NOX conversions (≥ ∼85%) at ≥ 220 °C and outperformed the control vanadia-tungstate on anatase, which was used to simulate a commercial catalyst. This paper remarks the exploration of the variable structures of metal vanadates can be a good strategy to discover high-performance catalytic solids for the reduction of NOX species.

Herein, we investigated the NOx reduction performance of Sb–V–CeO2/TiO2 (SbVCT) catalyst subjected to hydrothermal aging, where 6 vol% of H2O was fed to the SbVCT for 16 h with variable temperatures of 550–750 °C. The structural, morphological, redox, and acid properties of fresh and aged catalysts were comprehensively characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, N2-physisorption, temperature programmed reduction/desorption (H2–TPR/NH3/NO–TPD) and in situ DRIFTS. The XRD, Raman and TEM results of the fresh and the one hydrothermally aged at 550, 600 °C catalysts indicated the presence of finely dispersed polymeric vanadia, antimony, and nano-crystalline ceria species on TiO2 support. The SbVCT catalysts hydrothermally aged at the temperatures ≤ 600 °C showed better NOx conversions than the others aged > 600 °C. This was because aging at the temperatures ≤ 600 °C could help to minimize the loss of surface redox/acid properties that were originally inherent to surface vanadyl and CeO2 species that went into CeVO4 and large CeO2 aggregates. This in turn led to the loss of surface redox and acidic characters indigenous to the SbVCT and reduced its NOx reduction performance. Moreover, the NOx reduction performance of hydrothermally aged V–WO3–TiO2 catalyst, when compared with that of SbVCT catalyst, showed relatively low NOx conversions at the temperatures below 300 °C.

Manganese-based catalysts have attracted much attention due to their excellent performance for NO reduction with NH3 (NH3-SCR) at low temperatures. In the current study, the novel metal Sb was modified into Mn/TiO2 and Fe–Mn/TiO2, and the NO x conversion was compared with those of Mn/TiO2 and Fe–Mn/TiO2 catalysts to investigate the effect of the Sb. The NO x reduction activities of the catalysts were evaluated in the temperature range of 100–250 °C at a space velocity of 60,000 h−1. The physicochemical properties of all the catalysts were characterized by Brunauer–Emmett–Teller surface area, temperature-programmed desorption of ammonia, temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Interestingly, the Sb-promoted Mn-based catalysts showed significantly higher NO x conversion than the other catalysts with or without 6 vol% of H2O. The high performance of the Sb-modified catalysts could be related to the increase of acid sites and redox properties.

FeVO4 (Fe1) is a particular class of metal vanadate that has recently been highly profiled as an active site to selectively reduce NOX with NH3 (NH3-SCR). This primarily results from NOX/NH3-accessible VO43− anions and an electronic inductive effect between the Fe and V species, leading to the formation of abundant catalytic defects available for NOX turnover. Motivated by a structural inspection of the vanadates reported to date, this study detailed the use of Fe2V4O13 (Fe2) as a novel active site deposited on anatase (TiO2) for NH3-SCR. While providing the aforementioned structural benefits, Fe2/TiO2 also enhanced the redox character as well as the number of sites accessible to NOX/NH3 over Fe1/TiO2 because of the greater electronic inductive effect of Fe2. Therefore, Fe2/TiO2 converted NOX better than Fe1/TiO2 in the presence of H2O. To further improve the NH3-SCR performance of Fe2/TiO2, its catalytic surface was modified via two steps. The first step was to incorporate 1.9 wt% Sb into Fe2/TiO2. Sb could promote the redox feature of Fe2/TiO2 and help its surface to preferentially interact with NH3/NOX, thereby making the resulting Fe2–Sb1.9/TiO2 outperform Fe2/TiO2 during NH3-SCR in the presence of H2O. The second step was to functionalize the Fe2–Sb1.9/TiO2 surface with SO32−/SO42− species. The resulting Fe2–Sb1.9/TiO2 (S) was validated to further increase redox cycling of Fe2–Sb1.9/TiO2, favor NO2 production from NO oxidation for fast NH3-SCR, and hamper surface interplay with SO2. Fe2–Sb1.9/TiO2 (S), therefore, showed higher NOX conversions than a control simulating a commercial catalyst during NH3-SCR feeding H2O and SO2. Fe2–Sb1.9/TiO2 (S) also showed greater durability than the control because of its enhanced resistance to SO2, ammonium (bi)sulfates, and alkali metals.

The challenge for selective catalytic reduction (SCR) of NO with NH3 is to develop a proven catalyst with satisfactory performance and sulfur resistance at low temperatures. Two types of surface reaction properties have been shown to be involved in the W-Ce (VWCeTi) and Sb-Ce (VSbCeTi) systems. That is, active species have improved catalytic activity and the decomposition of ammonium bisulfate (ABS)/ammonium sulfate (AS) by the functionalization as well as the surface reactive oxygen (surface lattice oxygen/highly dispersed oxygen). The Sb-Ce system resulted in greater catalyst surface functionalization, generated the bulk-like cerium sulfate species and improved the active site by the sulfate effect. This system promoted the release of more reactive oxygen and surface lattice oxygen by enhancing the interaction between Sb and Ce to form more active species, which was found to have a positive effect on catalytic ABS/AS decomposition.

In this work, the antimony promoted Vanadia-Ceria catalysts have been prepared by homogeneous precipitation method for the selective catalytic reduction of NOx with NH3. With an introduction of Sb into Vanadia-Ceria, the catalysts showed an improvement in the low temperature NOx conversion below 250 °C. These high activities of the Sb promoted catalysts were related to the increase of acid sites and redox properties of the catalysts, which were investigated by the NH3-TPD (temperature programmed desorption), H2-TPR (temperature programmed reduction) and in-situ NH3-DRIFTS (diffused reflectance infrared Fourier transformed spectroscopy) spectra. In addition, structural and morphological properties of these catalysts were examined by X-ray diffraction, BET surface area and FE-SEM (Field emission scanning electron microscopy). After the addition of Sb to Vanadia-Ceria, the increase of surface area with a smaller, uniform sized particles and high dispersion of vanadia were indicated in the optimized 4 wt.% V2O5–2 wt.% Sb-CeO2 catalyst. Furthermore, the Lewis and Bronsted acid sites were enhanced in the 4 wt.% V2O5–2 wt.% Sb-CeO2 catalyst to promote NOx conversion at a wide temperature range of 175–400 °C. XPS results also indicated an improvement in the active oxygen species of this catalyst due to the enhancement of surface oxidation species of V4+/V5+, Sb3+/Sb5+ and Ce3+/Ce4+.

The correlation between the morphology of catalyst supports and their effect on catalyst dispersion was investigated. The structure of two types of γ-alumina (γ-Al2O3) crystallite particles, rod-like and platelet-like alumina, were measured in 4 orders of length scales, from nanometer to micrometer, using ultra small angle neutron scattering (USANS) and SANS and quantitatively characterized with Hammouda's Generalized Guinier–Porod model. Pt nanoparticles tended to deposit in finer particles and had narrower particle size distribution on the rod-like alumina supports compared to the plate-like alumina supports due to geometrically restricted deposition areas and higher surface curvatures of the rod-like supports. The high diffusion barrier for Pt particles on the highly curved surfaces of the rod-like supports was attributed to be the reason why Pt particles were prevented from diffusing and clustering. While aggregates of the rod-like alumina supports were randomly dispersed without any specific orientation, resulting in high surface area, aggregates of the plate-like alumina supports consisted of a stack of 2–3 layers due to the high van der Waals forces between planar layers, resulting in low surface area. Pt/rod-like alumina supports showed more than 100% higher catalytic activities than Pt/platelet-like alumina supports in model three-way-catalyst (TWC) reactions of CO, NO, and C3H6 conversions at 200–250 °C. Control of shape and aggregation of catalytic support materials in nano–micrometer scale can be an important parameter to improve catalytic performance.

V2O5 contains V5+ accessible to NOX/NH3, thus having partial success in producing N2 via selective NOX reduction (SCR) and NH3 oxidation (SCO). V2O5, however, can be advanced by structural modification with rare-earth metal (RM) to form vanadate (RM1V1O4), wherein Lewis acidity of open V5+ is regulated by the type of RM along with the change in Bronsted acidity/redox character. Herein, TiO2-supported Ce1V1O4 served as adaptable platform, where half of Ce was replaced by RM (Tb, Er, or Yb) to form Ce0.5RM0.5V1O4 catalysts. The promotive effect anticipated by RM substitution for Ce0.5RM0.5V1O4 was insignificant at low temperatures. Conversely, high temperatures tuned the property of Ce0.5RM0.5V1O4 desirably. Ce0.5Er0.5V1O4 possessed the greatest Lewis acidity/redox feature, thus revealing the best performance in SCR/SCO at elevated temperatures. Hydro-thermal aging (HT) of the catalysts was repercussive to their properties to some extents and altered the kind of major surface sites for SCR/SCO. Bronsted acidity/redox trait primarily directed low-temperature SCR performance of Ce0.5RM0.5V1O4 (HT), yet, were the greatest in Ce0.5Er0.5V1O4 (HT). Meanwhile, Lewis acidity of Ce0.5RM0.5V1O4 (HT) dominated high-temperature SCR/SCO performance and again was the most desired in Ce0.5Er0.5V1O4 (HT). This paper demonstrated the vitality of RM innate to Ce0.5RM0.5V1O4 for accelerating SCR/SCO exposed to periodic HT.

In this work, the synthesis of Sb-V/CeO2–TiO2 catalyst was modified by controlling pH with the addition of monoethanolamine solution. All the catalysts were systematically investigated for NO x reduction with NH3 at different reaction conditions and then characterized by XRD, BET-surface area, X-ray photoelectron spectroscopy, NO-TPD, NH3-TPD, and H2-TPR. This modified synthesis method for the Sb-V/CeO2–TiO2 catalyst exhibited noticeably higher NO x reduction activity at low temperatures (

In this study, catalytic activity and thermal stability of the arc plasma deposited (APD) Pt nano-particles on A12O3 and CeO2-Al2O3 were compared with that of the conventionally prepared Pt/Al2O3. All the catalysts were characterized by BET-surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, CO-pulse chemisorption, H2-temperarture programmed reduction and X-ray absorption near edge spectroscopy. Through the quantum chemical calculations of different metal oxide support, CeO2 was identified as a suitable anchoring material with high energy level between the Pt species (Pt(0) and PtO(x)) on ceria. Subsequently, the results of XPS and XANES revealed the presence of abundant Pt(0) metal species in APD catalysts. The addition of ceria to Al2O3 support enhanced the dispersion of Pt nano-particles. The H2-TPR of Pt/CeO2-Al2O3 (APD) catalyst showed high-temperature reduction peaks corresponding to the interaction of Pt with ceria on alumina by Pt-O-Ce. Consequently, the Pt nano-particles deposited on CeO2-Al2O3 by APD attained strong thermal resistance at high temperatures. In addition, superior catalytic activities for CO and C3H6 oxidation and NO(x) reduction were obtained for the Pt/CeO2- Al2O3 (APD) catalyst.

A study of structural and mechanistic investigation of the Sb/V/Ce/Ti catalysts sulfated at different temperatures was carried out by X-ray absorption near edge spectroscopy (XANES) and diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS). The high temperature sulfated catalyst, especially Sb/V/Ce/Ti-S500 (sulfated at 500 °C temperatures), exhibited superior NO x conversion at low temperatures (150–200 °C) compared to Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300 (sulfated at 400 and 300 °C) catalysts. The Ce L 3 edge XANES spectra of Sb/V/Ce/Ti-S500 catalyst showed the formation of Ce(III) dominant sulfate species, resulting in the enhancement of Lewis and Bronsted acid strength. The formation of Ce(III) sulfate species on Sb/V/Ce/Ti-S500 catalyst was clearly indicated by Ce M 4,5 and S K edge XANES spectra peaks at 881.9 eV attributed to Ce 3+ oxidation state and 2481 eV assigned to S 6+ oxidation state of sulfate species. Furthermore, the in situ DRIFTS results revealed that the Lewis and Bronsted acid sites of Sb/V/Ce/Ti-S500 catalysts increased significantly, followed by Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300. At 200 °C, the reaction between the pre-adsorbed NH 3 species with NO + O 2 on sulfated catalysts exhibited the formation of mono-dentate, bi-dentate, bridging nitrates and NO 2 species. Meanwhile, the subsequent formation of NO 2 via NO oxidation was promoted on Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S500 catalysts, followed by surface interaction with adsorbed NH 3 to produce N 2 and H 2 O at low temperatures (

The dual-walled characteristic mesoporous hollow structures of Co3O4 are explored as an efficient catalytic material for CO oxidation. The hollow structures with exposed (111) facets and a high surface area are attractive for efficient catalytic performance. As a result, complete CO conversion was achieved at 70 °C and a conversion of about 90 % was maintained at 60 °C for more than 600 min.

Sulfur dioxide (SO2) is considered as a poisoning gas for NH3-SCR catalysts under real time conditions. However, it has revealed an obvious beneficial effect on the activity of CeO2 containing catalysts. Hereby we report the applied research in sulfation effect on low-temperature activity enhancement of CeO2-modified, Sb2O3–V2O5–TiO2 catalyst system pretreated with SO2 under oxidizing conditions at different temperatures for 2 h. We have elucidated the real insights via nature-property relationships of the species formed at various SO2 pretreatment temperatures (T = 300, 400 and 500 °C) with the help of advanced characterization techniques such as X-ray diffraction (XRD), temperature programmed reaction (NH3-TPD, NO-TPD and H2-TPR), BET surface area, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDS) and X-ray photoelectron spectroscopy (XPS). Our results indicated that SO2 pre-treatment at 500 °C led to the maximum favorable sulfation with cerium(III) sulfate as the major surface species.

Ultra-small ( V ), discharge condenser capacitance ( C ), and the number of plasma pulse shots ( n ) as controllable parameters. The average size of intrinsic nanoparticles generated by APD process was as small as 0.9 nm and deposited nanoparticles began to have crystal structures from the particle size of about 2 nm. V was the most sensitive parameter to control the size and coverage of generated nanoparticles compared to C and n . Size of APD deposited nanoparticles was also influenced by the nature of evaporating materials and substrates.

A systematic investigation of the effect of ceria loading over Sb-V2O5/TiO2 catalysts was carried out for the selective catalytic reduction (SCR) of NOx by NH3. The various ceria loaded Sb-V2O5/TiO2 catalysts were prepared by deposition precipitation and impregnation methods. Addition of 10% ceria to Sb-V2O5/TiO2 catalyst significantly enhanced the NOx conversion at wide temperature range of 220–500 °C. The 10% ceria loaded Sb-V2O5/TiO2 catalyst showed superior N2 selectivity (>95%) throughout the reaction temperatures. The physicochemical characteristics of the obtained catalysts were thoroughly characterized by BET surface area, X-ray diffractometry (XRD), temperature programmed desorption (TPD) of NO, SO2 and NH3, H2- temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The XRD results indicated the active components of antimony and vanadia were homogeneously dispersed over CeO2/TiO2. It was found that the addition of 10% ceria to Sb-V2O5/TiO2 could enhance the total acidity and redox properties of the catalyst, which lead to show higher NOx conversions at wide temperature window. In XPS studies, increase in intensity of the chemisorbed mobile oxygen peak was observed for ceria loaded catalysts. In particular, the DRIFT spectra of ceria loaded Sb-V2O5/TiO2 catalysts showed abundant Bronsted acid sites at 1436 and 1673 cm−1 band, which are responsible for high NOx conversion. Furthermore, the results of NO and SO2 TPD of 10% ceria loaded Sb-V2O5/TiO2 catalyst showed enhancement of NO adsorption and SO2 inhibition properties, which is thought to play a significant role in long term stability of the catalyst during SO2 on–off study for 38 h at 240 °C.

The Sb–CeO2/TiO2 (SCT) catalytic system with different vanadia loading (0–3 % w/w) was systematically investigated for removal of NO by NH3. A series of catalysts prepared by impregnation and deposition precipitation methods were thoroughly characterized physically, by BET surface area, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and chemically, by temperature-programmed desorption (NH3 and SO2-TPD), temperature programmed reduction (H2-TPR), and in-situ DRIFT study. NH3-TPD and H2-TPR results for 2 and 3 % vanadia-loaded Sb–CeO2/TiO2 catalysts revealed high total acidity and reducibility. As a result, both catalysts had high activity at low temperatures. At 240 °C for 20 h the 2 % vanadia-loaded Sb–CeO2/TiO2 catalyst was more resistant to SO2 than the 3 % vanadia catalyst. In addition, in-situ SO2 DRIFT study revealed the existence of more surface sulfate species on Sb–CeO2/TiO2 than on vanadia-loaded Sb–CeO2/TiO2 catalysts.

The effect of Ce-loading over Sb-V2O5/TiO2 catalysts was investigated for the removal of NOx by NH3. In order to understand the influence of Ce-loading over Sb-V2O5/TiO2, NH3-temperature programmed desorption, H2-temperature programmed reduction, X-ray photoelectron spectroscopy (XPS) and diffused reflectance infrared fourier transformed spectroscopy (DRIFTS) were carried out. The 10 % Ce-loaded Sb-V2O5/TiO2 catalyst exhibited superior activity than commercial V2O5–WO3–TiO2 under 6 % H2O and 800 ppm SO2. The XPS results indicated the presence of Ce3+ species. The amount of Bronsted acid sites significantly increased as a result of Ce-loading. The DRIFT spectrum of Sb-V2O5/TiO2 catalyst indicated a peak at 1,363 cm−1, which corresponded to intermediates of ammonia oxidation species at 350 °C. Experimental results suggest that high NOx conversion and N2 selectivity of 10 % Ce-loaded Sb-V2O5/TiO2 was attributed to enhanced acidity and reducibility.

We report the catalytic activity of Au/TiO2 and Pt/TiO2 nanocatalysts under CO oxidation fabricated by arc plasma deposition (APD), which is a facile dry process involving no organic materials. Using APD, the catalyst nanoparticles were well dispersed on the TiO2 powder with an average particle size of 2–4 nm, well below that of nanoparticles prepared by the sol–gel method (10 nm). We found that the average particle size of the dispersed gold nanoparticles can be controlled by changing the plasma discharge voltage of APD. Accordingly, the amount of gold loaded on the TiO2 powder increased as the discharge voltage increased, but the specific surface area of the Au/TiO2 samples decreased. As for catalytic reactivity, Au/TiO2 showed a higher catalytic activity than Pt/TiO2 in CO oxidation. The catalytic activity of the Au/TiO2 samples showed size dependence where higher catalytic activity occurred on smaller gold nanoparticles. This study suggests that APD is a simple way to fabricate catalytically active nanocatalysts.

In this study, catalytic activity and thermal stability of the arc plasma deposited (APD) Pt nano-particles on A12O3 and CeO2-Al2O3 were compared with that of the conventionally prepared Pt/Al2O3. All the catalysts were characterized by BET-surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, CO-pulse chemisorption, H2-temperarture programmed reduction and X-ray absorption near edge spectroscopy. Through the quantum chemical calculations of different metal oxide support, CeO2 was identified as a suitable anchoring material with high energy level between the Pt species (Pt(0) and PtO(x)) on ceria. Subsequently, the results of XPS and XANES revealed the presence of abundant Pt(0) metal species in APD catalysts. The addition of ceria to Al2O3 support enhanced the dispersion of Pt nano-particles. The H2-TPR of Pt/CeO2-Al2O3 (APD) catalyst showed high-temperature reduction peaks corresponding to the interaction of Pt with ceria on alumina by Pt-O-Ce. Consequently, the Pt nano-particles deposited on CeO2-Al2O3 by APD attained strong thermal resistance at high temperatures. In addition, superior catalytic activities for CO and C3H6 oxidation and NO(x) reduction were obtained for the Pt/CeO2- Al2O3 (APD) catalyst.

The smart design of nanocatalysts can improve the catalytic activity of transition metals on reducible oxide supports, such as titania, via strong metal–support interactions. In this work, we investigated two-dimensional Pt nanoparticle/titania catalytic systems under the CO oxidation reaction. Arc plasma deposition (APD) and metal impregnation techniques were employed to achieve Pt nanoparticle deposition on titania supports, which were prepared by multitarget sputtering and sol–gel techniques. APD Pt nanoparticles with an average size of 2.7 nm were deposited on sputtered and sol–gel-prepared titania films to assess the role of the titania support on the catalytic activity of Pt under CO oxidation. In order to study the nature of the dispersed metallic phase and its effect on the activity of the catalytic CO oxidation reaction, Pt nanoparticles were deposited in varying surface coverages on sputtered titania films using arc plasma deposition. Our results show an enhanced activity of Pt nanoparticles whe...

Economic production of titanium dioxide (yield >98 %) from ilmenite has been achieved by use of a modified sulfate reduction process. A series of samples were prepared by varying the concentration of titanium dioxide nuclei (0.2, 0.3, and 0.6 %) and further impregnation with antimony and vanadia. The structural and acidic properties of the samples were comprehensively studied by X-ray diffraction (XRD), transmission electron microscopy, BJH pore size distribution, and temperature-programmed desorption of NH3. The XRD results revealed the presence of intense peaks from anatase titanium dioxide. Enhancement of surface area was observed for second-time filtered samples, possibly because of loss of iron from the bulk. As a result, formation of additional micropores was apparent from N2 adsorption and desorption isotherms. Among all the antimony and vanadia-doped samples, the first-time filtered sample with the low concentration of nuclei (0.2 %) had the highest catalytic activity at low temperatures, owing to its larger pore size and abundant acidic species.

A study of the lean NO x reduction activity in the presence of SO 2 and water over alkali promoted Ag/Al 2 O 3 catalysts has been done using methane as a reductant. The alkali doped materials are synthesized by the co-impregnation method. Their promotional behavior, existence of several silver species and improved adsorption properties have been thoroughly investigated by various techniques: XRD, XANES, TEM, UV–Vis DRS, SO 2 TPD and NO TPD. The evaluated samples exhibited high surface area around 220 m 2 g −1 . TEM results demonstrated the presence of highly dispersed nano sized silver particles on surface, where the addition of alkali metals slightly enhanced the crystallization of silver. Moreover, standard XRD profiles of fresh and used samples indicate the high durability and mechanical strength of catalysts. These findings are in line with the time-on-stream studies. The XANES results revealed that the edge spectra of prepared materials are similar to that of the reference Ag 2 SO 4. From XANES and UV–Vis DRS, the presence of crystalline Ag 0 and Ag + species were identified. Poor activity of Na promoted sample is attributed to absence of suitable amount of ionic silver compounds. However, the synthesized alkali doped materials showed the promotional deNO x conversions in the presence of SO 2 and H 2 O stream. Among the investigated samples K–Ag/Al 2 O 3 and Cs–Ag/Al 2 O 3 exhibited higher NO x conversions and thermal stability. The higher SCR of NO x was explained by the NO adsorption properties identified from the NO TPD studies.

This paper characterizes the integrated activity of fresh and used catalysts on the selective catalytic reduction of NOx using CH4. The synthesised K–Ag/Al2O3 catalysts exhibited a promotional effect on deNOx activity in the presence of SO2. In addition, 130 h of time-on-stream reactions demonstrated the thermal and mechanical stability of the synthesised materials. A TEM analysis and diffraction patterns demonstrated the sintering of finely dispersed particles to ~0.5 micron size clusters by sulphation. Furthermore, under reaction conditions, the de-sulphation initiated the re-dispersion of the Ag clusters to different sized particles. The TPD studied demonstrated the strong adsorption sites for methane and formation of R–SOx compounds. This surface modification in the SO2 feed stream is considered to be the reason for the promotional effect on the deNOx reaction.

A series of plate type anodic alumina (γ-Al 2 O 3 ) supported Cu and Cr catalysts were employed to investigate their reactivity in the partial oxidation (PO) of dimethyl ether (DME) in a microreactor. The effect of metal concentration and reaction temperature on DME conversion to hydrogen was assessed. It was found that conversion of DME to hydrogen by PO depends both on reaction temperature and active metal concentration. The catalysts were characterized by surface area (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) techniques. The metal loading as active component was investigated by electron probe micro analysis (EPMA) and X-ray fluorescence spectroscopy (XRF). The results showed that Cu as active component on γ-Al 2 O 3 possessed better activity than Cr. Further, the catalytic activity of Cu was enhanced in the presence of Cr. The XRD and XPS analysis indicated that enhanced Cu activity in the presence of Cr could be correlated to the partial existence of CuCr 2 O 4 along with CuO.

Highly active and selective alumina-supported Pt dendrimer-encapsulated nanocomposite materials were successfully prepared and evaluated for the selective catalytic reduction (SCR) of NOx using methane as reductant. The physicochemical properties of the prepared samples were investigated with X-ray diffraction (XRD), Brunauer Emmett Teller (BET) surface area, inductively coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy-energy-dispersive X-ray analysis (EDX) techniques. The resulted metallic Pt40 particles are spherical and well separated from each other. As derived from the transmission electron microscopy images, the average particle diameter of dendrimer-encapsulated nanoparticles (DENs) is 2.4 nm. The diffraction profiles of fresh and used catalysts indicated that the prepared materials are highly stable after 40 h of time-on-stream reaction. For DENs Pt/Al2O3 sample, the distribution of platinum particle size ranged between 2 and 20 nm. In the present investigation, the ...

Electricity is generated by the combined reactions of hydrogen oxidation and oxygen reduction which occur on the Pt/C catalyst surface. There have been lots of researches to make high performance catalysts which can reduce Pt utilization. However, most of catalysts are synthesized by wet-processes and a significant amount of chemicals are emitted during Pt/C synthesis. In this study, Pt/C catalyst was produced by arc plasma deposition process in which Pt nano-particles are directly deposited on carbon black surfaces. During the process, islands of Pt nano-particles were produced and they were very fine and well-distributed on carbon black surface. Compared with a commercialized Pt/C catalyst (Johnson & Matthey), finer particle size, narrower size distribution, and uniform distribution of APD Pt/C resulted in higher electrochemical active surface area even at the less Pt content.

In the present study, potassium and caesium doped Ag/ catalysts were synthesized by simple wet impregnation method and evaluated for selective catalytic reduction (SCR) of NOx using methane. TEM analysis and diffraction patterns demonstrated the finely dispersed Ag particles. BET surface measurements reveal that the prepared materials have moderate to high surface area and the metal amount found from ICP analysis was well matching with the theoretical loadings. The synthesized K-Ag/ and Cs-Ag/ catalysts exhibited a promotional effect on deNOx activity in the presence of and . The long-term isothermal studies at under oxygen rich condition showed the superior catalytic properties of the both alkali promoted samples. The crucial catalytic properties of materials are attributed to NO adsorption properties detected by the NO TPD.

A series of TiO2–ZrO2 supported V2O5 catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073 K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773 K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO2–ZrO2 support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO2–ZrO2 and V2O5/TiO2–ZrO2 catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti4+ and Zr4+ were noted with increasing thermal treatments. Vanadium oxide stabilized as V4+ at lower temperatures, and the presence of V5+ is observed at 1,073 K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600–708 K. The TiO2–ZrO2 support exhibits very less conversion of o-xylene, while 12 wt% V2O5 loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.

The partial oxidation of dimethyl ether (DME) was investigated using the structured catalyst Rh/Al2O3/Al. The porous Al2O3 layer was synthesized on the aluminum plate through anodic oxidation in an oxalic-acid solution. It was observed that about 20 nm nanopores were well developed in the Al2O3 layer. The thickness of Al2O3 layer can be adjusted by controlling the anodizing time and current density. After pore-widening and hot-water treatment, the Al2O3/Al plate was calcined at 500 degrees C for 3 h. The obtained delta-Al2O3 had a specific surface area of 160 m2/g, making it fit to be used as a catalyst support. A microchannel reactor was designed and fabricated to evaluate the catalytic activity of Rh/Al2O3/Al in the partial oxidation of DME. The structured catalyst showed an 86% maximum hydrogen yield at 450 degrees C. On the other hand, the maximum syngas yield by a pack-bed-type catalyst could be attained by using a more than fivefold Rh amount compared to that used in the structured Rh/Al2O3/Al catalyst.

The influence of sulfate on the selective catalytic reduction of on the Ag/ catalyst was studied when was used as a reducing agent. Various preparation methods influenced differently on the activity. Among the methods, cogelation precipitation gave best activity. When sulfates were formed on the surfaces of samples prepared by impregnated and deposition precipitation, activity was enhanced as long as suitable forming condition is satisfied. The major sulfate formed in Ag/ catalyst was the aluminum sulfate and it seems that this sulfate acted as a promoter. When Mg was added to the Ag/ catalyst it promoted activity at high temperature. Intentionally added sulfate also enhanced activity, when their amount was confined less than 3 wt%.

Dendrimer encapsulated Pt nanoparticles were prepared by using hydroxyl terminated generation four (G4OH) PAMAM dendrimers (DEN) as the templating agents. The encapsulated Pt nanoparticles were dispersed on γ-Al2O3 at room temperature by impregnation. Pt/Al2O3 (DEN) catalysts were then subjected to thermal treatments in oxidizing and reducing atmospheres at different temperatures. These catalysts were characterized by Transmission Electron microscopy (TEM) and In situ Fourier-Transform Infrared (FTIR) spectroscopy. The TEM analysis of the as synthesized catalysts revealed that the Pt nanoparticles were found to be 2–4 nm in size. It is observed that the Pt particle size in 0.5% Pt/Al2O3 (DEN) catalyst increased upon thermal decomposition of the dendrimer. The in situ FTIR results suggested that the presence of oxygen and the Pt nanoparticles in the Pt-dendrimer nanocomposite accelerate the dendrimer decomposition at low temperatures. All the catalysts were tested for the reduction of NO x with CH4 in the temperature range of 250–500 °C. NO x reduction efficiency of Pt/Al2O3 (DEN) catalysts were compared with the Pt/Al2O3 (CON; conventional) catalyst. The conversion of NO x was started from the low temperatures over Pt/Al2O3 (DEN) catalysts. The high selectivity of NO x to N2 of 74% was obtained over 0.5% Pt/Al2O3 (DEN) catalyst at low temperatures around 350 °C.