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Cold-start emissions significantly contribute to total vehicular pollutant emission profiles. There has therefore been a significant amount of research focused on catalytic aftertreatment systems that can mitigate CO, hydrocarbon and NO emissions at low temperatures. Recently, passive NO adsorbers (PNAs) have been developed, and these can store or trap NO at low temperature and are designed to release the trapped NO at higher temperature ranges, where downstream NO reduction catalysts are active. Pd/BEA is reported to be one such PNA. In this study its NO storage at low temperatures and release at higher temperatures was characterized using temperature programmed (TP) experiments and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The influence of CO was investigated and was shown to improve the amount stored at low temperature and also induce higher temperature desorption, in a range that is applicable for downstream NO reduction. Without the reductant, NO release primarily occurred at temperatures too low to be practically relevant. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The effect of Cu loading on the selective catalytic reduction of NO by NH was examined over a series of Cu ion-exchanged (20-80%) SSZ-13 zeolite catalysts. High NO reduction efficiencies (80-95%) were obtained over all catalyst samples between 250 and 500 °C, and at the gas hourly space velocity of 200,000 h. Both NO reduction and NH oxidation activities under these conditions were found to increase slightly with increasing Cu loading at low temperatures. However, NO reduction activity was suppressed with increasing Cu loadings at high temperatures (>500 °C) due to excess NH oxidation. The optimum Cu ion exchange level appears to be ~40-60% since higher than 80% NO reduction efficiency was obtained over 50% Cu ion-exchanged SSZ-13 up to 600 °C. The NO oxidation activity of Cu-SSZ-13 was found to be low regardless of Cu loading, although it was somewhat improved with increasing Cu ion exchange level at high temperatures. During the 'fast' SCR (i.e., NO/NO = 1), only a slight improvement in NO reduction activity was obtained for Cu-SSZ-13. Regardless of Cu loading, near 100% selectivity to N was observed; only a very small amount of NO was produced even in the presence of NO. The apparent activation energies for NO oxidation and NO SCR were estimated to be ~58 and ~41 kJ/mol, respectively. Graphical Abstract: [Figure not available: see fulltext.]. [ABSTRACT FROM AUTHOR]

Nickel doped manganese oxide supported on titania materials were investigated for the low-temperature NH-SCR. For this purpose, a series of Ni modified Mn/TiO catalysts were prepared and evaluated for the low-temperature SCR of NO with ammonia in the presence of excess oxygen. The catalytic performance of these materials was compared with respect to the nickel weight percentage in order to examine the correlation between physicochemical characteristics and reactivity of optimized materials. It was found that the 5% Mn-2% Ni/TiO catalyst showed the highest activity and yielded 100% NO conversion at 200 °C. XRD results reveal highly dispersed manganese-nickel species on TiO support for the Mn-Ni/TiO catalysts. Our TPR data results suggested an increase in reducibility of manganese species in Mn-Ni/TiO catalysts. The absence of the high-temperature (736 K) peak indicates that the dominant phase is MnO. This increase of reducibility and dominant MnO phase seems to be the reason for the enhanced activity and time on stream patterns of nickel-promoted titania-supported manganese catalysts. BET results illustrate that the high NO conversion is strongly dependant on the specific surface area and pore volume of this catalyst. All the physicochemical techniques we used suggested that the composition of manganese and nickel oxides on the support surface is playing an important role for the enhancement of NO conversion and the prominent time on stream stability. [ABSTRACT FROM AUTHOR]

In-Fe loaded sulfated zirconia (SZ) was firstly studied for the selective catalytic reduction (SCR) of NO with methane and exhibited higher activity than In/SZ and Fe/SZ. The addition of iron to the In/SZ increases its surface area and strong acid sites, which can be helpful for the SCR of NO. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A series of VO-MnO/TiO-CNTs, VO/TiO-CNTs, and MnO/TiO-CNTs catalysts were synthesized via solvothermal method and their NO removal activities were studied. A catalytic performance improvement was observed over catalysts prepared by mechanical mixing MnO/TiO-CNTs and VO/TiO-CNTs. XRD, SEM, EDS, TPD, TPR, and BET were employed to analyze the improvement which is ascribed to the separation of Mn and V as well as the increase in reducibility and acidic strength. Graphical Abstract: The existence of catalytic activity promotion between VO and MnO was clarified by TOF. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ag-promoted Co-ZSM-5 catalyst was prepared and tested for the selective catalytic reduction of NO with methane. The low-temperature activity and water-resistant ability of the promoted catalyst were markedly improved in comparison to Co-ZSM-5. The NO conversion was about 100% in the temperature range of 350-550 °C at a space velocity of 6,000 h and nearly 60% in the presence of 2% water steam. The results showed that with Ag presence, the redox nature of cobalt species changed. The improvement of low-temperature activity and water-resistance of catalyst is attributed to the suppression of methane combustion and the formation of surface nitrate species. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Gold supported on alumina catalysts were investigated for selective NO reduction by propene. Two types of alumina, commercial and sol-gel alumina, were employed. The catalytic performance was mainly studied over the impregnated sol-gel alumina catalyst. The catalytic activity was tested under various propene and oxygen concentrations. NO conversion and the activity window of the catalysts increased as the propene or oxygen concentration increased. The presence of water also enhanced the NO conversion and widened the activity window of the catalysts. The sol-gel alumina supported catalysts gave much higher activity than the commercial alumina supported catalysts. Graphical Abstract: Catalytic activity of gold supported on alumina prepared from various techniques.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this work we studied the effect of acidity and of oxygen on the reduction of NO with CH on Pd sulphated zirconia and alumina supports under reducing and oxidizing feed conditions. The acidity of sulphated zirconia (SZ) is higher than sulphated alumina (SA). The surface acids are Lewis sites and are responsible for the NO dissociation. The introduction of Pd affects the acidity and surface area. The conversion of NO is higher on the Pd/SA than on Pd/SZ catalyst under reducing condition. The addition of O increased the oxidation of methane. The NO molecules are adsorbed dissociatively into N and O species. The higher acidity inhibits the dissociation and reaction over the metallic Pd particles. Oxygen favored the oxidation of Pd particles and influences negatively the NO conversion. Graphical Abstract: Effect of acidity and oxygen on the reduction of NO with CH on Pd sulphated zirconia and alumina supports. The introduction of Pd affects the acidity and surface area. The NO molecules are adsorbed dissociatively on the Pd/SA but not on the Pd/SZ. The higher acidity inhibits the dissociation and reaction over the metallic Pd particles. Oxygen favored the oxidation of Pd particles and influences negatively the NO conversion. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The article discusses a study which investigates how the copper and cerium oxide deposition on alumina influence the activity of the prepared catalysts in the reduction of nitric oxide and carbonic oxide. It conducted chemical analysis and adsorption characterization. It is concluded that the method of preparation leads to the formation of different surface groups on the samples contain different mass percentage of copper and cerium.

The role of Ag in simultaneously catalyzing NO reduction and C3H6 oxidation was shown to be strongly dependent on the redox properties of its local environment. Under an atmosphere of 1,000 ppm NO, 3,000 ppm C3H6, and 1% O2 and a GHSV of 30,000 h−1, a perovskite La0.88Ag0.12FeO3 prepared by reactive grinding is active giving a complete NO conversion and 92% C3H6 conversion at 500 °C. These values are much higher than the NO conversion of 55% and C3H6 conversion of 45% obtained over a 3 wt.% Ag/Al2O3 catalyst under the same conditions. Under an excess of oxygen (10% O2) a good SCR performance with a plateau of N2 yield above 97% over a wide temperature window of 350–500 °C along with C3H6 conversion of 90% at 500 °C was observed over Ag/Al2O3, while minor N2 yields (∼10% at 250–350 °C) and high C3H6 conversions (reaching ∼100% at 450 °C) were obtained over La0.88Ag0.12FeO3. Abundant molecular oxygen is desorbed from Ag substituted perovskite after 10% O2 adsorption as verified by O2- temperature programmed desorption (TPD). This reflects the strongly oxidative properties of La0.88Ag0.12FeO3, which lead to a satisfactory NO reduction at 1% O2 due to the ease of nitrate formation but to a significant C3H6 combustion above that value. The formation of nitrate species over the less oxidizing Ag/Al2O3 was accelerated under an excess of oxygen resulting in an excellent lean NO reduction behavior. The redox properties of silver catalysts could be adjusted via mixing perovskite with alumina for an optimal elimination of both NO and C3H6 over the whole range of oxygen concentration between 0 to 10%. [ABSTRACT FROM AUTHOR]

A simple molecular beam instrument (MBI) was fabricated for measuring the fundamental parameters in catalysis such as, sticking coefficient, transient and steady state kinetics and reaction mechanism of gas/vapor phase reactions on metal surfaces. Important aspects of MBI fabrication are given in detail. Nitric oxide (NO) decomposition and NO reduction with carbon monoxide (CO) on Pd(111) surfaces were studied. Interesting results were observed for the above reactions and they support the efficiency of the MBI to derive the fundamental parameters of adsorption and catalysis. Sustenance of CO oxidation at 400 K is dependent mostly on the absence of CO-poisoning; apparently, CO + O recombination is the rate determining step ≤400 K. NO adsorption measurements on Pd(111) surface clearly indicating a typical precursor kinetics. Displacement of the chemisorbed CO by NO on Pd(111) surfaces was observed directly with NO + CO beams in the transient kinetics. It is also relatively easy to identify the rate-determining step directly from the MBI data and the same was demonstrated for the above reactions. [ABSTRACT FROM AUTHOR]

Contact of adsorbed ammonium nitrite, NH4NO2, with HCl vapor or a solid acid such as the zeolite HY, significantly lowers the temperature of its decomposition to N2 + H2O. Protonated NH4NO2 decomposes at room temperature. The decomposition of ammonium nitrite is one of the steps in the catalytic reduction of NO x with ammonia or other reductants. [ABSTRACT FROM AUTHOR]

Mono – (Ag/SiO2, Pd/SiO2) and bimetallic (Ag+Pd/SiO2) catalysts have been obtained via sol-gel method from tetra-ethoxy-silane (TEOS) and their activity in reduction of Nitric oxide (NO) with carbon monoxide (CO) has been investigated. The highest activity in the process of reduction of NO with CO possesses the sample Ag + Pd/SiO2. It has been found that the sol-gel method for preparation of bimetallic catalysts allows the formation of various catalytic active centers (CAC) which leads to high activity in reaction of NO reduction. The presence of Ag2O and PdO in these CAC allows the elimination of NO. The process of this elimination includes reduction of NO with CO at temperatures up to 200 оC as well as direct decomposition of NO at higher temperatures. [ABSTRACT FROM AUTHOR]

An unusual behavior was observed during experiments conducted at 371 and 465 °C with a commercial NOX storage/reduction catalyst: the outlet NOX concentration during the trapping phase reached a cycle minimum after regeneration, increased for 20–30 s, as expected, but then surprisingly decreased, indicating the catalyst had become more efficient in trapping the entering NOX. The results reported in this letter indicate that this phenomenon was caused by a superposition of two factors: a substantial exotherm associated with the regeneration event from reductant reacting with surface oxygen species and a negative impact of an evolving temperature profile on the dynamic NOX storage capacity. [ABSTRACT FROM AUTHOR]

The ability of H2S to reduce NO in a fixed bed reactor using a γ-alumina catalyst was studied with the objective of generating new methods for conversion of NO to N2. Compared to the homogenous reaction of NO with H2S, the catalyzed reaction showed improved conversions of NO to N2. Using a gas space velocity of 1000 h−1 and a feed of 1% NO and 1% H2S in argon, it was found that the conversion of NO to N2 was complete at 800 °C. This result compared to a 38% conversion of NO to N2 for the homogeneous gas phase reaction at 800 °C. At temperatures below 800 °C, a short fall in the nitrogen balance was discovered when the γ-alumina was employed as a catalyst. This discrepancy was explained by conversion of NO to NH3 and subsequent reaction of the NH3 with any SO2 in the system to form ammonium sulfur oxy-anion salts. This suggestion is supported by the finding that when larger amounts of H2S were used relative to NO, more NH3 was formed together in tandem with lower N2 mass balances. Several reaction pathways have been proposed for the catalytic reduction of NO by H2S. [ABSTRACT FROM AUTHOR]