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Simple strategy to stably preserve the smaller Ni nanoparticles (NPs) having homogeneous crystallite size of ∼5 nm was proposed using ordered mesoporous supports under dry reforming of methane with CO2 (DRM). The NPs-impregnated ordered mesoporous SBA-15 was effective to preserve the smaller Ni nanoparticles with their lower thermal aggregations and less coke depositions by their spatial confinement effects inside of the ordered mesopore structures compared to the irregular conventional SiO2 support. Although the highly ordered mesoporous NPs-impregnated Al2O3 was also found to be effective, the acidic natures of the Al2O3 surfaces accelerated coke depositions by preferentially forming inactive phases.

A new kinetic model for the synthesis of gasoline-range hydrocarbons from dimethyl ether over a nanostructured ZSM-5 catalyst was developed based on the dual-cycle reaction mechanism.

Cu-based catalysts have been variously used in the water gas shift reaction (WGSR) and methanol synthesis, both of which use carbon monoxide as a common reactant. According to the Bell–Evans–Polanyi principle, CO adsorption energies (Eads,CO) directly affect the activation energies for CO hydrogenation. Thus, the understanding of the relationship between Eads,CO and the chemical properties of the catalytic surface is fundamental to catalyst design. In particular, recent studies have shown that effective catalysts can be developed by controlling the exposed facets or forming alloys with other transition metal to enhance the mechanical and electronic characteristics. In bimetallic catalysts, two types of chemical effects are known to determine the adsorption energies: one is the “strain” effect caused by lattice mismatch and the other is the “ligand” effect, generated by the change in orbital electrons. We conducted calculations on Cu/M(100), (111), and (211) surfaces (M = Ni, Ir, Pd and Pt) by using spin-polarized density functional theory (DFT) calculations to find the dominant factor, as well as trends, affecting CO adsorption. Our calculations suggest the ligand effect is the dominant contribution to Eads,CO, regardless of the type of facets. We also determined that the ligand contribution is caused by the loss of electrons from the surface Cu atoms. As a result, a proportional correlation between ligand contribution and electron charge transfer was observed. On investigating the strain effect on the (111) facet, we found that the results are consistent with d-band theory, while the Eads,CO on (100) and (211) facets showed the opposite trend.

While cellulose nanofiber-based bioplastics are of great interest for replacing synthetic polymer and glass materials, the main limitation is their low thickness, which makes them difficult for various applications. In this study, we fabricated millimeter-scale thick bioplastic composites, based on 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (TEMPO-CNF) and epoxy resin, via sequential lamination processes. The glycerol as softener was added to TEMPO-CNF dispersion to prepare a thick TEMPO-CNF layer without shrinkage. It was discovered that the total thickness of TEMPO-CNF/epoxy laminates can be easily controlled by changing the thickness and number of TEMPO-CNF layers and the total thickness can also be easily increased up to 2.4 mm. Furthermore, these TEMPO-CNF/epoxy laminates have high flexural strength (272 MPa) as well as good transmittance (85% % at 600 nm). We anticipate that our approach will significantly broaden the strategies for fabricating nanocellulose-based bioplastics for use as a replacement for transparent synthetic polymers and glass materials.

The effects of hydrocarbons (HCs) on a combined selective catalytic reduction (SCR) system by NH3 and mixed HCs for simulated exhaust over five different types of Cu2+-exchanged zeolite catalysts h...

A series of CeO2-based catalysts were investigated for soot oxidation with O2. The macroporous CeO2 catalyst (M-CeO2) showed higher soot oxidation activity than mesoporous CeO2 due to the enhanced contact between catalyst and soot caused by the large pore size of M-CeO2. Moreover, various amounts of Ag (2–20 wt.%) were introduced to M-CeO2 to increase the activity, and the Ag-incorporated macroporous CeO2 catalysts (Ag(x)_M-CeO2) were characterized. Raman spectra showed that the ratio of active oxygen species (Oxn−) were different according to amount of Ag. The ratio of highly reactive superoxide (O2−) was largest for the Ag(5)_M-CeO2 catalyst, and then it was decreased as the Ag amount increased further. In addition, XPS analysis showed that the difference in Oxn− generation could be attributed to diverse surface oxygen vacancies in the catalysts. Hence, the amount of loaded Ag affected the surface oxygen vacancies of Ag(x)_M-CeO2 and consequently the ratio of Oxn− was different according to the surface oxygen vacancies of the catalysts. Ag(5)_M-CeO2 with the appropriate surface oxygen vacancies induced the promotion of O2− generation, resulting in the best soot oxidation activity. It was concluded that the amount of Ag on CeO2 has a great influence on the catalytic soot oxidation activity, and proper surface oxygen vacancies facilitated O2− generation, whereas excessive surface oxygen vacancies hindered the formation of highly reactive Oxn−.

While green bioplastic based on carbohydrate polymers have showed considerable promise, the methods typically used to prepare them in a single material have remained a significant challenge. In this study, a simple approach is proposed to fabricate high performance cellulose films composed of chemically and physically dual-crosslinked 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (DC TEMPO-CNFs). The hydroxyl groups of TEMPO-CNF suspensions were firstly crosslinked chemically with epichlorohydrin (ECH), and subsequently TEMPO-CNF matrices were crosslinked physically via the strong electrostatic interaction between carboxylate and Ca2+ ions. It was found that the optimized DC TEMPO-CNF films exhibit a good transmittance (90 %) and a high tensile strength (303 MPa). Furthermore, these DC TEMPO-CNF films revealed superior thermal stability and excellent water resistance compared to neat TEMPO-CNF films without crosslinked domains. We believe that these results will pave the way to preparing practical polysaccharide bioplastics with simple, environmentally-friendly manufacturing processes.

To achieve high fuel efficiency and low emission in automobiles, it is necessary to develop highly active diesel oxidation catalysts (DOCs). Pd/CeO

Owing to strengthened regulations toward vehicle emissions, the use of diesel particulate filter technology to reduce particulate matter emissions has attracted significant attention. To achieve low temperature oxidation of particulate matter, numerous studies on Ag/CeO

In our previous study, we conducted CO oxidation with SiO2@Pd@CeO2 catalysts. However, the limit of the CeO2 shell thickness limited the thermal stability. So, in this study, thick ZrO2 shell was introduced to improve thermal stability. SiO2@Pt@ZrO2 catalysts were examined for the simultaneous oxidation of CO and hydrocarbons. SiO2@Pt@ZrO2 catalysts had improved thermal stability compared to Pt/SiO2 or Pt/ZrO2 after aging at 750 °C for 25 h. However, fresh SiO2@Pt@ZrO2 catalysts showed low oxidation activity because of the low gas accessibility due to the thick ZrO2 shell. Therefore, we proposed etched SiO2@Pt@ZrO2 catalysts for enhanced gas accessibility. The selective etching of SiO2 was adjusted by varying the KOH concentration. TEM images confirmed that the void space of the core-shell catalysts increased as the concentration of KOH increased. The exposed Pt surface area increased as the void space of the core-shell catalysts was increased. On the other hand, in excessively etched 3.2 M catalysts, the core-shell structure collapsed. Etched catalysts which maintain the core-shell structure improve thermal stability after hydrothermal aging. As a result, 1.6 M catalysts showed the best simultaneous oxidation of CO and hydrocarbons, and we confirmed that properly etched catalysts enhanced the oxidation activity and thermal stability.

The effects of noble metal (M = Ag, Au, Pd, Pt, and Rh) on CeO

In previous studies, Ag/CeO2 catalyst showed the high activity on NOx-free soot oxidation. For additional improvement of oxidation activity, Mn was introduced in Ag/CeO2 and NOx-assisted soot oxidation was performed. NOx-assisted soot oxidation activities showed the large difference between the catalysts. Especially, Ag/2MnOx-1CeO2 catalysts showed remarkably improved T20 at 349 °C compared with T20 of Ag/CeO2 at 464 °C (each T50 is 391 °C and 400 °C, and each Tmax is 514 °C and 509 °C). NO oxidation activity was increased as the mole ratio of Mn increased, while amount of NO adsorption was increased in Ag/MnOx-CeO2 mixed oxide compared to other catalysts. Especially, Ag/2MnOx-1CeO2 catalysts showed NO oxidation activity at low-temperature and NO desorption at appropriate temperature. As a result, it was confirmed that not only the NO oxidation activity but also the NOx adsorption characteristics are the most important factors in NOx-assisted soot oxidation. Accordingly, Ag/2MnOx-1CeO2 catalysts were proposed as optimal catalysts.

The efficient methods to preserve original smaller nickel nanoparticles (NP) with its even size distribution of ∼5 nm on a highly ordered mesoporous SBA-15 (NP/SBA-15) were investigated for a high temperature (800 °C) dry reforming of methane with CO2 (DRM). The suppressed thermal aggregation with less coke deposition and higher catalytic activity were observed by the confined nickel nanoparticles spatially in the mesoporous SBA-15 channels. Especially, two-step surface-pretreated SBA-15 with acetic anhydride followed by successive H2O treatment showed a higher dispersion of organics-stabilized nickel nanoparticles, which were preferentially deposited in the ordered mesoporous inner SBA-15 channels with its insignificant aggregation. On the optimal NP(10)/SBA-15 with 10 wt%Ni possessing the characteristics of the hydrophobic SBA-15 inner surfaces, as-prepared nickel nanoparticles were selectively and homogeneously distributed in the inner mesoporous SBA-15 channels with its small depositions on the outer SBA-15 surfaces. The spatial confinement effects were realized due to the less mobility of the smaller nickel nanoparticles by keeping its original particle sizes even after a long-term DRM reaction at 800 °C for 120 h. The phenomena were responsible for an enhanced catalytic stability by suppressing a severe sintering of nanoparticles and less coke formation even under a harsh DRM reaction condition.

To achieve high fuel efficiency and low emission in automobiles, it is necessary to develop highly active diesel oxidation catalysts (DOCs). Pd/CeO2 catalysts have been widely used as active catalysts for CO and C3H6 oxidation reactions. Additionally, Ag has been reported to enhance the oxygen storage capacity (OSC) of CeO2, which contributes to the oxidation ability of Pd/CeO2. In this study, Pd/Ag-CeO2 catalysts were used for CO and C3H6 oxidation reactions. When CeO2 was doped with appropriate amounts of Ag, reducibility and CO desorption rate were increased, which confirmed the high OSCs of Ag-doped catalysts. However, Ag particles were formed and the Ce3+/Ce4+ ratio decreased when CeO2 was doped with excess amounts of Ag. In addition, reduced Pd (Pd0), which is an active species for C3H6 oxidation, was formed and maintained even under oxidative reaction conditions. Since the removal of C3H6 is important for the oxidation of CO and C3H6, the catalyst with the highest Pd0 fraction (Pd/0.1Ag-CeO2 and Pd/0.3Ag-CeO2) presented improved catalytic activity. Consequently, the optimal amount of Ag enhanced the OSC of Pd/Ag-CeO2 catalysts and formed active Pd0 species under oxidative conditions, which resulted in the excellent catalytic activity of Pd/Ag-CeO2 for the CO and C3H6 oxidation reaction.

Owing to strengthened regulations toward vehicle emissions, the use of diesel particulate filter technology to reduce particulate matter emissions has attracted significant attention. To achieve low temperature oxidation of particulate matter, numerous studies on Ag/CeO2 catalysts for soot oxidation have been reported. Herein, Ag/La-CeO2 catalysts with different La contents are synthesized and compared to analyze the effect of La. Hydrogen temperature programmed reduction analysis confirms that the reducibility increases with an increase in the La content in La-CeO2. X-ray photoelectron spectroscopy and Raman analysis confirm an increase of oxygen vacancies with La doping. Accordingly, the soot oxidation performances estimated by temperature programmed oxidation experiments increase with La doping. However, the catalytic activity of Ag/La-CeO2 exhibits a volcano trend. When an appropriate amount of La is incorporated in Ag/CeO2, peroxide generation and reducibility improve, thereby enhancing the soot oxidation performance. Conversely, the catalytic activities gradually decrease with excess La-doping. Scanning transmission electron microscopy analysis and density functional theory calculations confirm that excess amounts of La induce the sintering of Ag particles, which lead to the degradation of peroxide generation and reducibility of the catalysts. Consequently, an optimal amount of La incorporation on Ag/La-CeO2 results in the best soot oxidation performance.

To evaluate the usability of TiO

The effects of noble metal (M = Ag, Au, Pd, Pt, and Rh) on CeO2 in enhancing the activity toward soot oxidation were studied through experimental methods and density functional theory (DFT) calculations. Each noble metal (3 mol.%) was supported on CeO2 (M/CeO2) and the properties of the catalysts were verified by XRD, HRTEM, N2 physisorption, CO chemisorption, XPS, and H2-TPR results. The noble metal was highly dispersed over CeO2, except for Au due to the sintering of Au, and the reducibility of the catalysts was greatly improved according to degree of the interaction between each noble metal and CeO2. The activities of M/CeO2 catalysts for soot oxidation were better than that of CeO2, and followed the order Rh/CeO2 > Ag/CeO2 > Pt/CeO2 > Au/CeO2 > Pd/CeO2 > CeO2. Moreover, our DFT calculations showed that vacancy formation energy was gradually lowered in the following order: CeO2 > Pd4/CeO2 > Pt4/CeO2 > Au4/CeO2 = Ag4/CeO2 > Rh4/CeO2, which was similar order with experimental activity. In addition, the electronic states of the p and f orbitals of CeO2 were studied to compare with the occupied Ce 4f electrons, which affect the redox property. Rh/CeO2 and Ag/CeO2 showed the improved soot oxidation activity, with an enhanced ability to generate oxygen vacancy formation and oxygen adsorption and increased electron transfer. Consequently, the experimental and DFT calculation results revealed the roles of noble metals on ceria with respect to catalytic activity.

In this work, the promoting effects of Cu on Ag-loaded CeO2 catalysts on soot oxidation were investigated through a series of Cu-incorporated catalysts (AgCu(x)Ce) with various amounts of Cu. Ag particles were highly dispersed over Cu(x)Ce mixed oxide, and AgCu(x)Ce catalysts presented improved activity in comparison to Ag/CeO2. Raman spectra and H2-TPR showed that the complex effects of the Ag-CeO2 and CuO-CeO2 interactions enhanced the ability to generate highly active superoxide (O2−) and greatly improved the reducibility of AgCu(x)Ce catalysts. The amount of Cu affected degrees of both the Ag-CeO2 and CuO-CeO2 interactions, and consequently, the ratio of active oxygen species (Oxn−) and the reducibility of the catalysts varied. AgCu(0.4)Ce with adequate surface oxygen vacancies promoted the generation of O2−, and the promoting effects enhanced the reducibility, resulting in greatly improved activity. It is suggested that introduction of Cu to Ag/CeO2 significantly improves the activity of the catalyst and that the optimized Cu content induces positive interrelations, whereas excessive Cu hinders the improvement in catalytic performance due to decreased synergistic effects between the Ag-CeO2 and CuO-CeO2 interactions.

In this study, SiO2-supported Pd catalyst (Pd/SiO2) and CeO2-encapsulated Pd/SiO2 core-shell catalysts (SiO2@Pd@CeO2) were prepared and examined for CO oxidation. After aging at 700 ℃, the thermal stability of SiO2@Pd@CeO2 catalyst was improved in comparison to Pd/SiO2 because the CeO2 shell increased the structural stability and effectively inhibited the sintering of Pd particles on SiO2. Moreover, the differences in activity and properties of the catalysts were investigated through various characterization methods. The CeO2 shell induced changes in the chemical properties of the Pd particles adjacent to CeO2 due to the strong interaction between Pd and CeO2 (PdxCe1-xO2 solid solution), and the interaction improved the activity of the SiO2@Pd@CeO2 catalysts. As a result, the SiO2@Pd@CeO2 core-shell catalysts have an enhanced thermal stability and catalytic activity resulting from both a morphology effect and a synergistic effect between Pd and CeO2.

To evaluate the usability of TiO2 support for silver in soot oxidation, Ag/TiO2 and Ag/CeO2 catalysts were prepared and soot oxidation experiment was performed. The catalytic activity of silver was more enhanced on P25 and rutile than on anatase and CeO2 in tight contact, as evidenced from comparing the activities of supports and silver impregnated catalysts. The reasons for the difference in active metal enhancement were elucidated by various characterization methods (TEM, H2 TPR, and XPS), and it is verified that it resulted not from dispersion of silver but from oxidation ability. On the other hand, Ag/P25 showed poor activity in loose contact because of low contact between silver and soot. To improve the loose contact activity of the Ag/P25 catalyst, CeO2 was introduced for active oxygen delivery. The synthesized CeO2-Ag/P25 catalyst showed enhanced loose contact activity when compared with Ag/P25 and Ag/CeO2 due to synergistic effects from the active oxygen supply ability of silver on P25 and the oxygen transfer ability of loaded CeO2. Thermal stability of the catalyst was identified by recycling test to 800℃, and the maintained T20 and T50 demonstrated its durability for practical use in automobile exhaust removal.

TWC activity and thermal stability of LaAlO3-based Pd catalysts were investigated under simulated gasoline engine exhaust conditions. The LaAlO3-based catalysts revealed a stronger thermal stability than the conventional Al2O3-based ones. Pd-substituted for Al in the LaAlO3 perovskite structure exhibits a stronger thermal stability than that impregnated on the LaAlO3 surface. The increased electron density around Pd induced by the electron donation from the more electronegative La may enhance the thermal stability of PdO by suppressing the decomposition of PdO. The strong interaction between Pd and La appears also contributing to the improvement of the TOFs for the TWC reactions over the Pd-substituted LaAlO3 (i.e., LaAlPdO3) catalyst, as evidenced by CO-chemisorption, TGA, XPS, XANES, H2-TPR, DRIFT and TPD studies. CO and C3H6 oxidation reactions over the LaAlO3-based Pd catalysts are strongly structure-sensitive, while those over the Al2O3-based Pd catalysts are weakly structure-sensitive. The NO reduction and H2 oxidation reactions are strongly structure-sensitive over all the Pd-containing catalysts examined.

Ag-doped perovskite catalysts (La1−xAgxMnO3) prepared by the citric acid method were investigated for the catalytic oxidation of NO. Compared to LaMnO3, La1−xAgxMnO3 revealed a superior NO oxidation activity with its maximum activity at x = 0.2, confirming the potential of La0.8Ag0.2MnO3 as one of the most promising NO oxidation catalysts. The high reactivity of La0.8Ag0.2MnO3 is mainly due to the high oxygen vacancy concentration on its surface produced by the partial substitution of La3+ with Ag+ in LaMnO3, as determined by the XRD, SEM, XPS, O2-TPD, H2-TPR, (NO + O2)-TPRD and DRIFT studies. The mono- and bi-dentate nitrates formed on the oxygen vacancies of perovskite appear to be the primary reaction intermediates for the NO oxidation reaction over the Ag-doped perovskite catalyst. A plausible reaction pathway of the NO oxidation over La1−xAgxMnO3 has been postulated on the basis of the redox process involving the oxygen vacancy, oxygen, NO, NO2 and NO3.

A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (α) and NO (β), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations.

Gasoline particulate filters (GPFs) contain small amounts of O2 and excess H2O; however, the effect of H2O on soot oxidation has not been thoroughly explored to date. Thus, it is necessary to understand the effect of H2O on soot oxidation to improve the catalytic performance in GPFs. This study investigates the role of H2O in soot oxidation on macroporous Ce-Zr mixed oxide catalysts (M-CeZr). The results revealed an improvement in the catalytic activity of soot oxidation in the presence of H2O over that afforded under oxygen-only conditions. Since the mechanism of soot oxidation under dry conditions involves the conversion of gaseous oxygen to active oxygen (Ox−) species on the oxygen vacancies of the catalyst, Ox− and oxygen vacancy are critical factors that affect the catalytic performance in the absence of H2O. Notably, when H2O was introduced into the reaction, it was predominantly used as an oxidant rather than gaseous oxygen. Further, the dissociation of H2O into active oxygen over the catalyst surface was not related to the number of oxygen vacancies. Therefore, even when the catalyst comprised few oxygen vacancies, its activity improved under wet conditions. In addition, although the catalysts were damaged by high temperatures, the catalytic performance was maintained in the presence of H2O, unless the morphology of the catalysts collapsed.

A Mn–Fe/ZSM5 catalyst has been developed for removing NOx from diesel engine exhausts and its excellent low-temperature SCR activity and N 2 selectivity demonstrated in comparison with other representative SCR catalysts including CuZSM5 and a Cu-based commercial catalyst (COM). The well-dispersed MnO 2 and the high NH 3 adsorption capacity of the Mn–Fe/ZSM5 catalyst have been identified as the primary sources for its high deNOx activity for NH 3 /SCR. Hydrothermal stability and durability of the Mn–Fe/ZSM5 catalyst have been examined and compared to those of the CuZSM5 and COM catalysts. The hydrothermal stability of the catalyst improved upon the increase of Mn content and/or the addition of Er, the latter of which helps to stabilize the dispersion of MnOx on the catalyst surface during hydrothermal aging. The deNOx activity of the Mn–Fe/ZSM5 and its Er-promoted counterpart was less affected by HC poisoning, C 3 H 6 poisoning in particular, compared to the CuZSM5 and COM catalysts, mainly due to the excellent C 3 H 6 oxidation activity of MnO 2 . No poisoning of the Mn-based ZSM5 and CuZSM5 catalysts has been observed upon the addition of 2 wt.% of K + and Ca 2+ to their surface, primarily due to the high NH 3 adsorption capacity of the ZSM5 support, whereas the COM catalyst has been severely deactivated by the deposition of K + and Ca 2+ . The deNOx activity of the Mn-based ZSM5 catalyst, particularly the Er-promoted one, was less affected by SO 2 compared to the CuZSM5 and COM catalysts, although it was hardly regenerated at 500 °C. Formation of MnSO 4 on the catalytic surface appears to be the primary cause for the deactivation of the Mn-based ZSM5 catalysts in the presence of SO 2 in the feed gas stream.

The catalytic activity and thermal durability of Rh supported on a variety of metal oxides for removing NOx in the three-way catalyst (TWC) converter have been investigated under realistic gasoline engine exhaust conditions. Among the Rh/metal oxide catalysts examined, the Rh/ZrO2 catalyst has the best thermal durability. The catalytic activity and thermal stability of the Rh/ZrO2 catalysts have shown strong dependence on the ZrO2 support employed, with the ZrO2 prepared by the sol–gel (SG) and precipitation (P) methods exhibiting the most favorable catalytic performance. The improved TWC performance and thermal stability of the Rh/ZrO2 (SG and P) catalysts compared to other Rh/ZrO2 catalysts are mainly due to the structural difference in the underlying ZrO2 supports. Both ZrO2 (P) and ZrO2 (SG) contain the tetragonal as well as the monoclinic phase of ZrO2, whereas the others are primarily in the monoclinic phase. Deactivation of the Rh/ZrO2 upon thermal aging is mainly caused by the loss of the active metal surface area of Rh due to sintering and/or burial of Rh into the sublattice of ZrO2. The strong interaction of Rh with the tetragonal phase of ZrO2 appears to prevent the burial of Rh into ZrO2 lattice during the thermal aging. A series of comparative kinetic experiments revealed that the Rh/ZrO2 (SG and P) catalysts among other Rh/metal oxide catalysts produce the least amount of harmful NH3, which can be subsequently oxidized to hazardous NOx over the Pd-based oxidation catalyst co-existing in the TWC converter. A dual-brick monolith system washcoated with Rh/ZrO2 (P) and Pd/Al2O3 in the front and the rear bricks, respectively, has shown superior thermal durability over monolith configurations investigated in the present study.

The effect of C 3 H 6 on the deNO x activity of CuZSM5, FeZSM5 and V 2 O 5 /TiO 2 catalysts by NH 3 has been examined. The catalytic NO removal activity decreased by the continuous inclusion of C 3 H 6 into the reactor feed gas stream. The higher the feed concentration of C 3 H 6 , the more severe the retardation of the catalyst activity. The primary cause for the inhibition is the competitive adsorption of NH 3 and C 3 H 6 onto the catalyst surface and the useless consumption of NH 3 by the side reaction, including the NH 3 oxidation and ammoxidation reactions during the course of NH 3 /SCR reaction with C 3 H 6 .

The deactivation of a three-way catalyst (TWC) included in warm-up catalytic converters (WCC) employed in passenger vehicles has been examined with respect to the catalyst field mileage by drivers. By a sweep test (ST) under the A/F oscillation of 1 Hz simulating the actual operation of a gasoline engine, the gradual deactivation of CO oxidation activity under rich condition over the Pd TWCs customer-aged was clearly observed with respect to the catalyst mileage, while the oxidation activity of C3H6 had been hardly altered. No proportional dependence of the deactivation of the CO and C3H6 oxidation activity on the catalyst mileage, however, was determined by both a steady-state sweep test (st-ST) and a light-off test (LOT) without A/F perturbation, although the initial deactivation of both reactions by both test modes was apparent. The sintering of noble metal (NM) itself might not be the only cause for the deactivation of TWC with respect to the catalyst aging mileage. The gradual alteration of the oxygen storage capacity (OSC) of TWC, mainly due to the degradation of the oxygen storage components and the weakness of the Pd-Ce interaction, is also the cause for TWC deactivation, particularly for the CO oxidation reaction under rich condition. No deactivation of the oxidation reaction of C3H6 by ST, regardless of the catalyst mileages is likely due to the strong oxidative capability of Pd toward hydrocarbons.

To enhance the chlorine tolerance of copper ion exchanged mordenite (CuHM) catalyst under NH3-SCR reaction condition when HCl exists in the feed gas stream, mainly from a waste incinerator, a second metal, particularly cerium, has been additionally exchanged onto the catalyst along with Cu. It prevents Cu(II) ion from being evaporated from the catalyst surface by HCl and significantly improves the catalyst deactivation. The loss of copper from CeCuHM catalyst has been observed at a reaction temperature of 450 °C, while that from CuHM catalyst without Ce begins at 350 °C. Ce simply stabilizes Cu(II) ion on the catalyst surface, generally recognized as an active reaction site for the present reaction system. X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), synchrotron radiation X-ray diffraction (SR-XRD), and X-ray photoelectron spectroscopy (XPS) have been employed to identify the stabilization of Cu(II) ion on CuHM catalyst by Ce. As confirmed by SR-XRD, the lattice parameters of the unit cell of CeCuHM catalyst are less altered than those of CuHM catalyst without Ce during the course of the catalyst deactivation. Similarly, as identified by XPS, Cu(II) on the surface of CeCuHM catalyst is less transformed to Cu(I) ions. Ce ions and Ce–Cl compounds formed on the catalyst surface may decrease the average electronegativity of the catalyst and increase the charge of the lattice oxygen in the zeolite framework, resulting in an enhancement of the stability of the Cu–O bond in the present catalytic system.

The deactivation characteristics of copper ion exchanged mordenite type zeolite catalyst (CuHM) by HCl for the reduction of NO x , particularly from an incinerator with NH 3 , have been investigated over a fixed bed flow reactor system. X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), synchrotron radiation X-ray diffraction (SR-XRD), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD) have been employed to illustrate the deactivation mechanism of CuHM by HCl due to the formation of the deactivation precursor through the reaction between HCl and Cu on the catalyst surface. Cu 2 Cl(OH) 3 has been identified as the precursor for the present reaction system and can also be converted to CuCl 2 ·2H 2 O during the course of the reaction, particularly at high reaction temperature. XANES and EXAFS analyses reveal that the oxidation state of Cu ion on CuHM catalyst is mainly divalent, regardless of the degree of the catalyst deactivation. However, XPS study provides evidence for an increase of the content of Cu(I) ion on the surface of the catalyst deactivated at 450 °C for 110 h. Moreover, CuCl 2 ·2H 2 O that forms on the catalyst surface during the course of the reaction evaporates at a reaction temperature higher than 350 °C. It eventually converts to CuCl and then it may evaporate to the bulk gas stream and/or introduce a copper ion onto the zeolite surface again through solid-state ion exchange.

The effect of tungsten and barium on the thermal stability of V2O5/TiO2 catalyst for NO reduction by NH3 was examined over a fixed bed flow reactor system. The activity of V2O5/sulfated TiO2 catalyst gradually decreased with respect to the thermal aging time at 600 °C. The addition of tungsten to the catalyst surface significantly enhanced the thermal stability of V2O5 catalyst supported on sulfated TiO2. On the basis of Raman and XRD measurements, the tungsten on the catalyst surface was identified as suppressing the progressive transformation of monomeric vanadyl species into crystalline V2O5 and of anatase into rutile phase of TiO2. However, the NO removal activity of V2O5/sulfated TiO2 catalyst including barium markedly decreased after a short aging time, 6 h at 600 °C. This may be due to the transformation of vanadium species to inactive V–O–Ba compound by the interaction with BaO which was formed by the decomposition of BaSO4 on the catalyst surface at high reaction temperature of 600 °C. The addition of SO2 to the feed gas stream could partly restore the NO removal activity of thermally aged V2O5/sulfated TiO2 catalyst containing barium.

The stability of mordenite-type zeolite catalyst by hydrochloric acid was examined to remove NOx contained in the flue gas from an industrial waste incinerator. Cu ion-exchanged mordenite (CuHM) catalyst was is easily deactivated under selective catalytic reduction reaction conditions when water and HCl simultaneously exist in the flue gas. The deactivation of CuHM catalyst is mainly caused by the evaporation of Cu ions from the framework of mordenite structure. To enhance the acidic tolerance of the catalyst, the Si/Al ratio of the catalyst was controlled and second metals were added to the catalyst. Such a modification significantly improved the deactivation of the catalyst by HCl, commonly contained in the flue gas from the industrial waste incinerator as well as NO.