Trimodal porosity was generated in a spent coffee ground-derived biochar structure due to the synergistic effect between lanthanum and zinc, resulting in a lactic acid yield of 14% over 10% Ti–0.5% Nb/AC.

This study examines the impact of the composition, texture and structure of sodium- and calcium-rich bentonite clays further exchanged with cobalt cations and then combined with a polyaniline-type polymer, with the aim of obtaining an efficient photocatalyst for the degradation of methyl orange azo dye in wastewater under natural sunlight irradiation. The structural, textural and optical properties, as well as the differences between the resulting nanostructures were evaluated using X-ray diffraction, UV–Visible and infrared spectroscopy, scanning electron microscopy coupled to energy-dispersive spectroscopy, and nitrogen physisorption. The photocatalytic activity enhancement observed on the nanocomposites has been attributed mainly to their lower band gap energy (Eg = 2.31 eV for polyaniline/cobalt-modified purified calcium bentonite clay (PAn/Co-PBC-c) and Eg = 2.14 eV for polyaniline/cobalt-modified purified sodium bentonite clay (PAn/Co-PBC-s)), enhancement of visible light absorption, less recombination of electron–hole induced by incorporation of bentonite modified with cobalt cations, surface heterogeneity and more open porosity, resulting in methyl orange photodegradation rates of 31.5

The influence of cobalt substitution in the Fe3O4 spinel structure on the catalytic properties in methane oxidation under lean and stoichiometric conditions has been studied in the presence and in the absence of water. An interesting kinetic feature was related to a weak inhibiting effect of water on methane conversion on CoxFe3-xO4 mixed oxides. Remarkable catalytic properties were obtained for the composition Co2FeO4 characterized by two Fe-rich and Co-rich spinel structures. A partial replacement of Fe3+ by Co3+ in octahedral sites induces an elongation of the Co-O bond improving the mobility of oxygen species and the reducibility of Co3+ cations. Subsequent gain in methane conversion is obtained on Co2FeO4 pre-reduced at 250 degrees C in H2. At this reduction temperature, the structural properties seem not altered. A significant cobalt enrichment is observed which could be responsible of improved catalytic properties in connection with the stabilization of highly reducible Co3+ species and anionic vacancies conductive for the reaction. On the other hand, extensive reduction at 500 degrees C leads to strong deactivation likely related to the disappearance of the cubic spinel structure associated to a loss of oxygen mobility.

The Three-Way Catalytic performances of Pd supported on dual-substituted LaFeO3 catalysts have been studied from temperature-programmed experiments in typical TWC operating conditions. La has been partly substituted by Ca and Fe by Cu. Pd was introduced simply by wet impregnation. Particular attention was paid to the structure and composition of La-substituted by calcium and A-deficient perovskites to stabilize palladium dispersion and oxidation state. Weak interactions between oxidic Pd species and LaFeO3 lead the prevalence of metallic Pd species which are responsible of the highest metallic Pd dispersion. In contrast, much less reducible oxidic Pd species can be stabilized in defective sites characteristic of La-deficient et Ca-substituted perovskite structures then improving oxygen mobility. The changes in reaction rates, activation energies, and selectivities for oxidation and reduction reactions would solely reflect the participation of Pd as active sites on Pd/LaFeO3, while the cooperative effect between palladium and surface oxygen species belonging to the perovskite lattice would be responsible for the superior performance of Pd/La1− xCaxFe0.8Cu0.2O3. The practical interest of this composition is emphasized through the comparison with a benchmark Pd/CexZr1−xO2 catalyst.

Nickel-promoted molybdenum carbide (Mo2C) catalysts supported on γ-Al2O3 were synthesized via incipient wetness impregnation and evaluated for dry methane reforming (DMR). Comprehensive physicochemical characterizations including XRD, SEM-EDS, H2-TPR, XPS, TPSR, and TG-DSC were conducted to elucidate structure-performance relationships. Non-promoted Mo2C exhibited poor catalytic stability due to oxidation during DMR. The incorporation of nickel significantly enhanced catalytic activity and stability by promoting the in-situ re-carburization of oxidized Mo species and facilitating methane activation. The optimized Ni/Mo molar ratio of 1:1 led to the formation of a stable Ni-Mo synergistic phase, which exhibited superior resistance to sintering and deactivation.

The kinetics of the CH4/O-2 reaction was studied in lean conditions on Natural-Gas-Vehicle Pd-doped LaMnO3 catalysts. The impact of the method for Pd incorporation, sol-gel vs. impregnation, has been examined. The calcination temperature to obtain the perovskite structure turned out to be a key to determine the strength of the interaction between Pd and LaMnO3. Steady-state kinetic measurements at 400 degrees C have been modeled according to a single site or a dual site reaction mechanism representative of the cooperation between Pd and surface lattice oxygen species supplied by the support material. Impregnated catalysts are found sensitive to particle sintering inducing a deterioration of the metal-support interface. On the contrary, aging leads to strenghening of the metal-support interaction on sol-gel Pd catalysts which promotes methane conversion notably near three-way operating conditions.

The photocatalytic degradation of methyl orange has been studied under visible light. The combination of polyaniline and montmorillonite doped by cobalt and nickel cations enhanced the photocatalytic activity compared to pristine polyaniline. Kinetic measurements have been tentatively explained on the basis of their composition, electronic structures, structural and textural properties. Separate experiments performed on doped montmorillonites show weak performances, reflecting their insulating behaviour, altered by diffusion limitations. A pseudo-first order agrees with a weak methyl orange adsorption. More open porosity of composite materials led to improved efficiency. Their superiority compared to doped montmorillonites has been preferentially related to surface heterogeneity, stronger methyl orange adsorption and lower band gap energy.

The kinetics of the CH 4 /O 2 reaction, occurring on post-combustion catalysts to treat the exhaust gases of natural gas-powered engines, has been investigated in lean conditions on model Pd catalysts supported on K-doped LaMnO 3 . Experimental and predicted reaction rates have been compared according to a single site on Pd active sites and dual site reaction mechanism on active sites located at the Pd-perovskite interface. Comparisons with a benchmark Pd/LaMnO 3 emphasized significant changes induced by thermal aging at 750 degrees C in wet atmosphere (10 vol% H 2 O in 5 vol% O 2 ). Indeed, the contribution of the single site mechanism grows on aged Pd/LaMnO 3 emphasizing a deterioration of the Pd-LaMnO 3 interface. The opposite trend is observed on Pd/La 1_ x K x MnO 3 with kinetics obeying to a single site mechanism on pre-reduced catalyst and then shifting to a quasi-exclusive dual site mechanism after aging. Such kinetic features have been discussed with respect to bulk and surface physicochemical characterization pointing out the key role of potassium in the stability of the Pd-support interface.

The effect of La-deficiency and Ce/Sr-substitution in the benchmark LaCo0.8Fe0.2O3 has been investigated for the decomposition of N2O between 500 and 900 degrees C. Real inlet gas composition and space velocity reveal that La-deficiency and Ce/Sr-substitution can improve the thermal stability of catalyst, while La1-xSrxCo0.8Fe0.2O3 with x >= 0.1 was highlighted as a promising formula due to the strongest resistance to deactivation and suppressed undesired NOx decomposition at high space velocity. This phenomenon is mainly ascribed to the incorporation of Sr2+ into the perovskite lattice during the reaction consequently stabilizing the Co3+ species and creating the oxygen vacancies in La1-xSrxCoO3-delta. On the contrary, the loss of activity on Ce-substituted LaCo0.8Fe0.2O3 has been preferentially related to the cobalt exsolution to extra framework of perovskite making the catalytic cycle with Co3+ unfavorable. All these bulk and surface changes are accompanied with opposite evolution of apparent activation energy and pre-exponential factor which can be discussed based on a redox mechanism.

More stringent regulations on air pollutant emissions from engines fuelled by diesel and gasoline inevitably raise the question of the future of this type of motorization. Indeed, significant additional economic efforts by car manufacturers would be needed for compliant, that could be detrimental for their competitiveness. The promising alternatives are associated to the generalization of electric motorization. However, it will not be effective in the short and medium term. An intermediate scenario lies in the development of internal combustion engines powered by less harmful gaseous fuels towards environment. This review examines the different schemes and scenarios associated to this transition regarding the necessary adaptations on the existing catalytic after-treatment technologies. More stringent regulations on air pollutant emissions from engines fuelled by diesel and gasoline inevitably raise the question of the future of this type of motorization.

Trace N2O emissionsNO emission in ammonia burnerAmmonia burner during the nitric acid productionNitric acid production process have received special attention as N2O is recognized as a potent greenhouse gasGreenhouse gas that actively participates in global warmingGlobal warming. The abatement of N2O complies to international commitments aiming to reduce the greenhouse gas emissionsGreenhouse gas emissions through the installation of appropriate technologies. Different strategies have been categorized, the most efficient one involving the implementation of heterogeneous catalytic reactorHeterogeneous catalytic reactor in various positions of nitric acid plantNitric acid plant. The catalystCatalyst compositionComposition strongly depends on the running temperatureTemperature privileging mixed-metal oxidesMixed metal oxide for N2O decompositionNO decomposition at medium and high-temperatureTemperature whereas PlatinumPlatinum GroupGroup Metal-supported catalystsCatalyst can be preferred for end-of-pipeEnd-of-pipe technologies running at low temperatureTemperature with the help of reducing agentReducing agent. This present chapter focusses on medium and high-temperatureTemperature (350–900 °C) applicationApplication. Different theoretical and experimental approaches will be discussed in order to get more insights into the design of active sitesActive site, especially under more realistic running conditions to improve the understanding of kineticsKinetic and get more relevant reactionReaction mechanisms that could further provide guidelines for the preparation of more stable and selective catalystsCatalyst.

Increasingly stricter regulations for vehicle emissions require more competitive exhaust emission control systems. Three-way catalysis is a major up-to-date emission control technology, though the activity could be limited during the cold start as well as steady state operation including the three regimes: rich (λ<1), lean (λ>1), and stoichiometric (λ=1). Periodic rich/lean switching emerges as a promising strategy to address this challenge. In this work, we investigate the influence of the switching process, using a fixed lambda air-to-fuel ratio amplitude of λ = 1±0.02 (0.5 Hz), on pollutant conversion from 100 to 400 °C, under a complex matrix including nitrogen monoxide (NO), carbon monoxide (CO), hydrogen (H2), and hydrocarbons (C1-C5), simulating the typical car exhaust gas. Moreover, two catalysts were tested: one homogeneously coated with Pd, and another zone-coated with Pd, both containing the same total amount of Pd, in order to identify the effect of the catalyst zone-coating and rationalize the use of increasingly scarce platinum group metals. Simple binary pollutant oxidation reactions were also performed to determine the reactivity of individual pollutant gases. Interestingly, NO, CH4 and C5H12 displayed highest conversions during the switching regime compared to steady-state periods, attributed to the beneficial balance between active site poisoning/regeneration during the rich/lean regimes respectively. The zone-coated catalyst showed an overall higher activity under the full gas mixture that could be explained by a slightly higher Pd content, more effective Pd-support interactions, exothermic effect or the better OSC properties.

The kinetics of the catalytic CH4/O-2 reaction has been studied on 1 wt% Pd/LaxMnO3 with x = 0.7, 1.0 and 1.3. Steady-state kinetic measurements have been performed in lean conditions at 400 degrees C on pre-reduced and on aged catalysts after exposure to wet atmosphere at 750 degrees C. A single site reaction mechanism occurs preferentially on Pd/La1.3MnO3 exhibiting a La-rich surface. In contrast a dual-site reaction mechanism, combining Pd and surface reactive oxygen species from the support, is preferentially involved on Pd-La0.7MnO3 characterized by a Mn-rich surface. Pd/LaMnO3 exhibits a mixed regime but subsequent deterioration of the Pd-LaxMnO3 interface during thermal aging leads to increasing contribution of the single site reaction mechanism. High surface Pd/Mn ratio and high concentration of Pd-n(+) with n > 2 can be considered as good descriptors to probe the efficacy of Pd/LaxMnO3 catalysts. Remarkably, the high thermal stability of the Pd-La0.7MnO3 interface, preserving the Pd dispersion on Pd/La0.7MnO3, leads to lower sensitivity to deactivation.

The SCR performance of V2O5-WO3/TiO2 SCR-catalysts characterized by different surface W density (2.1W/nm2 and 9.5W/nm2) and different surface V density varying in the range 1–8V/nm2 has been investigated in order to clarify existing controversies on the preferential involvement of electronic and geometric effects in the catalytic properties. It was found that tungsten has a weak effect on the VOx cluster size distribution through contraction of dilution effect. In contrast, the optimal interaction between W and V, when both reach their highest composition, appears to be a relevant parameter that can enhance their acidic properties and improve the catalytic efficiency in dry conditions. On the other hand, an absence of significant interaction leads to discontinuity due to deactivation. In the presence of steam, acidic properties are averaged, lowering the impact of the V to W ratio. Finally, the critical importance of acidic properties which outperform redox properties in the definition of active site is pointed out in the light of this study.

The catalytic combustion of methane is a key reaction taking place on Natural Gas Vehicle three-way catalysts in unfavorable stoichiometric and rich operating conditions. Pd-doped LaxMnO3 based materials have been developed. Their efficacy has been studied on the basis of the following parameters: La-composition (x = 0.7 or 1), homogeneity of perovskite composition according to the protocol synthesis (sol–gel vs. combustion method), strategy for Pd incorporation. The control of Pd dispersion is closely related to the method used for Pd addition. Stabilization of Pd inside the perovskite lattice through a sol–gel route outperforms classical wet impregnated samples in terms of catalytic activity. This trend is accentuated on La-deficient composition as the creation of defective sites can strengthen the Pd–LaxMnO3 interaction. The best compromise was found on La0.7Mn0.98Pd0.02O3.

Methane oxidation has been studied on Rh/Ce x Zr 1− x O 2 . Catalytic performances were found highly sensitive to the preparation method of Ce x Zr 1− x O 2 support. Coprecipitation method leads to the highest conversion and the lowest activation barrier suggesting improved metal-support interaction. In contrast, weak resistance to thermal aging is observed. Finally aged coprecipitated Rh/Ce x Zr 1− x O 2 mimics the kinetic behavior of catalysts prepared by crystal templating method. Kinetic measurements performed on this latter catalyst show that a single site reaction mechanism is more appropriate compared to dual site mechanism which agrees with the assumption that deactivation of coprecipitated samples would be related to the suppression of the metal-support interface.

New insights into reaction mechanism for catalytic methane combustion are provided in broad operating conditions on Pd/La0.7MnO3 as model natural gas vehicle catalyst. Under lean and dry conditions, a dual mechanism is suggested with active sites combining reactive oxygen species from La0.7MnO3 and palladium instead of single site reaction mechanism. Aging in wet atmosphere has no consequence on the kinetic behavior. On the other hand, in wet atmosphere near the stoichiometry, strong accumulation of hydroxyl groups on the support would suppress the metal-support interface. Accordingly, methane combustion would take place only on Pd particles.

Monolith-shaped three-way catalysts (TWC) are always at the edge of science and technology as a response to the stringent updates on the emission standards worldwide. In spite of rapid research on TWC materials, the exact compositions adapted by major automotive companies are not fully known. This study focuses on comparing two fresh commercial monolithic catalysts for gasoline engines, namely, monolith-A and monolith-B, to highlight the significance of their manufacturing strategies by its characterization and catalytic evaluation under realistic lean/rich/stoichiometric regimes. Firstly, monolith-A demonstrates a zoning on its front and back side with high Pd and Rh loading to enhance CO/HC oxidation and NOx reduction, respectively, having higher amounts of trace dopants like La, Y, Pr and S. Whereas, monolith-B has a homogeneous composition with much lower noble metal/trace elements content without any Pr and S. Secondly, the double-layer washcoating is employed by following different routes with distinct compositions of alumina and ceria-zirconia. Monolith-B showed better low temperature CO oxidation performance while monolith-A performed better for NOx reduction owing to higher Rh loading. Overall, the zoning strategy of monolith-A raises question on its cost effectiveness in regards to its performance while poor reduction capabilities is exhibited by monolith-B. This study highlights that the latest TWC strategies have a scope of further development particularly with respect to the catalytic performance/expense ratio.