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The individual and simultaneous removal of NOx by Storage and Reduction with H2 (H2‐NSR) and combustion of soot have been studied for La and CuLa catalysts. The NOx storage capacity of pure lanthanum oxide is improved either by copper addition or by using a colloidal crystal hard template for the synthesis of a macroporous structure. Although the NOx storage capacity of the CuLa macroporous material is around ten times lower regarding conventional PtBa catalysts, the kinetics of the H2‐NSR cycles are fast enough to allow high NOx removal (until 90 % removal). Lanthanum oxide catalyst prepared with uncontrolled structure has no activity for soot combustion, but the activity increases for a macroporous counterpart prepared using the colloidal crystal template because the macroporous structure improves the soot‐catalyst contact and allows the nitrogen‐oxygen surface groups yielded upon NOx chemisorption to oxidize soot. The soot combustion activity of lanthanum catalysts is also enhanced upon copper loading, because copper improves the NO2‐assisted soot combustion mechanism and favors the chemisorption of NOx, enhancing soot oxidation by nitrogen‐oxygen surface species. Finally, it is demonstrated that the simultaneous removal of NOx by H2‐NSR and soot combustion can be carried out with a CuLa catalyst at 450 °C. The simultaneous removal does not affect the combustion of soot and only has a small effect in NOx removal. [ABSTRACT FROM AUTHOR]

A new concept, referred to as key‐lock catalyst, is presented in this article. Soot combustion ceria catalysts were prepared combining hard (polymethylmethacrylate colloidal crystals) and soft (Pluronic F127) templates, tuning the porosity of ceria in different size ranges to match the morphology of soot aggregates. The catalysts porosity was characterized in detail by N2 adsorption‐desorption isotherms and Hg‐porosimetry. XRD and H2‐TPR characterization ruled out that differences in activity are related neither with crystallographic nor with redox properties. As a proof of key‐lock catalyst concept, an optimum key‐lock ceria catalyst was synthesized by combining large macropores (100–300 nm) with mesopores (10–30 nm), because they fit to the large soot aggregates and to primary soot particles sizes, respectively. The best soot combustion activity of the optimum key‐lock catalyst is attributed to the optimum transfer of ceria active oxygen from catalyst to soot. The catalytic results confirmed that all ceria catalysts prepared with different porosity oxidize NO to NO2 at the same rate, and the NO2‐assisted soot combustion pathway is not affected by tuning ceria porosity. This double‐templated synthesis and the key‐lock concept opens a new synthesis approach to design noble‐metal free soot combustion catalysts based on the highly effective active oxygen mechanism. [ABSTRACT FROM AUTHOR]

Ni/CeO 2 catalysts are very active and selective for total hydrogenation of CO 2 to methane, but the nature of the active sites is still unclear. The surface of a Ni/CeO 2 catalyst has been monitored under CO 2 methanation conditions by Near Ambient Pressure-XPS (NAP-XPS) using synchrotron radiation, and has been concluded that t he species involved in the redox processes taking place during the CO 2 methanation mechanism are the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ pairs. In addition, a small fraction of nickel is present on the catalyst surface forming NiO and Ni2+-carbonates/hydroxyls (around 20% of the total surface nickel), but these species do not participate in the redox processes of the methanation mechanism. Under CO 2 methanation conditions the H 2 reduction rate of the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ couples is much faster than their CO 2 reoxidation rate (2 times faster, at least, at 300ºC), but a certain proportion of nickel always remains oxidized under reaction conditions. The high activity of Ni/CeO 2 catalysts for CO 2 methanation is tentatively attributed to the simultaneous presence of Ni2+-CeO 2 and Ni0 active sites where CO 2 and H 2 are expected to be efficiently dissociated, respectively. [Display omitted] • The redox processes during CO 2 methanation involve the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ pairs. • H 2 reduction rate of the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ couples is faster than their CO 2 reoxidation rate. • Ni/CeO 2 catalysts keep simultaneously Ni2+-CeO 2 and Ni0 active sites under reaction conditions. • NiO and Ni2+-carbonates/hydroxyls do not participate in redox processes [ABSTRACT FROM AUTHOR]

[Display omitted] • CO 2 methanation kinetics on low-loaded Ni/Al 2 O 3 catalyst is described based on DRIFTS and kinetic data. • LHHW rate equations are deduced including the role of water, carbonyls and formates. • Formates decomposition as RDS rate equation represents most accurately the kinetic performance. • The participation of both carbonyls and formates in the CO 2 hydrogenation is confirmed. The mechanism and kinetic of CO 2 methanation reaction of 9.5 % Ni/Al 2 O 3 catalyst is analysed under a wide range of operating conditions. Once the catalyst activity is stabilized, the influence of temperature, total pressure and space velocity is studied for kinetic characterisation. A data set comprising of 153 experimental runs has been used to develop a kinetic model capable to accurately predict the reaction rate. Ni/Al 2 O 3 catalyst shows an apparent activation energy of 80.1 kJ mol−1 in CO 2 hydrogenation. Data obtained under differential mode adjust quite precisely to a power-law model with H 2 O inhibition, with a water adsorption constant of 3.1 atm−1 and apparent orders of 0.24 and 0.27 for H 2 and CO 2 , respectively. Based on DRIFTS results, we propose for the first time the H-assisted CO formation route, which is compared with the more conventionally reported carbonyl route, and describe the corresponding reaction rate LHHW equation, resulting in notable improvement for mean deviation (D) of 7.0 % in our model related to that based on the carbonyl route (D = 20.1 %) usually suggested for catalysts with higher Ni loads around 20 %. The H-assisted CO formation route considers the formate species decomposition into carbonyls via H-assisted CO formation mechanism and further carbonyls hydrogenation into CHO as the rate determining step. Thus, the LHHW mechanism, in which carbonyls as well as formate species participate in CO 2 methanation, is capable to reflect the kinetics of lowly-loaded Ni/Al 2 O 3 catalyst with high accuracy under relevant process conditions (315−430 °C, 1−6 bar, H 2 to CO 2 molar ratios between 1–16 and, different reagents and products partial pressures). [ABSTRACT FROM AUTHOR]

The preferential CO oxidation (so-called CO-PROX) is the selective CO oxidation amid H2-rich atmospheres, a process where ceria-based materials are consolidated catalysts. This article aims to disentangle the potential CO–H2 synergism under CO-PROX conditions on the low-index ceria surfaces (111), (110) and (100). Polycrystalline ceria, nanorods and ceria nanocubes were prepared to assess the physicochemical features of the targeted surfaces. Diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) shows that ceria surfaces are strongly carbonated even at room temperature by the effect of CO, with their depletion related to the CO oxidation onset. Conversely, formate species formed upon OH + CO interaction appear at temperatures around 60 °C and remain adsorbed regardless the reaction degree, indicating that these species do not take part in the CO oxidation. Density functional theory calculations (DFT) reveal that ceria facets exhibit high OH coverages all along the CO-PROX reaction, whilst CO is only chemisorbed on the (110) termination. A CO oxidation mechanism that explains the early formation of carbonates on ceria and the effect of the OH coverage in the overall catalytic cycle is proposed. In short, hydroxyl groups induce surface defects on ceria that increase the COx–catalyst interaction, revealed by the CO adsorption energies and the stabilization of intermediates and readsorbed products. In addition, high OH coverages are shown to facilitate the hydrogen transfer to form less stable HCOx products, which, in the case of the (110) and (100), is key to prevent surface poisoning. Altogether, this work sheds light on the yet unclear CO–H2 interactions on ceria surfaces during CO-PROX reaction, providing valuable insights to guide the design of more efficient reactors and catalysts for this process. [ABSTRACT FROM AUTHOR]

• The optimum Ru loading for Ru/CeO 2 CO 2 methanation catalysts is 2.5 wt. %. • 2.5 wt. Ru/CeO 2 is reduced at the lowest temperature. • 2.5 wt. Ru/CeO 2 achieves the highest proportion of ruthenium cations with strong interaction with ceria. • 2.5 wt. Ru/CeO 2 combines good CO 2 chemisorption capacity with efficient further hydrogenation. • The balance between formation and hydrogenation of surface carbon intermediates is optimum for 2.5 wt. Ru/CeO 2. The conversion of CO 2 towards added valuable products is considered as a potential alternative to achieve the increase of the petrochemical industry while reducing the CO 2 emissions. In the present work, the effect of Ru loading on CeO 2 supports has been studied for the CO 2 methanation reaction, and catalysts with different Ru loading in the 1–5 wt. % range have been prepared, characterized, and tested. The optimum Ru loading has been found to be 2.5 wt. %. Ruthenium cations are reduced at the lowest temperature for this optimum loading according to H 2 -TPR experiments (even at room temperature), and the highest proportion of ruthenium cations with strong interaction with ceria is achieved, as deduced from XPS. XRD characterization suggests partial insertion of ruthenium cations into the ceria lattice. In situ DRIFTS experiments evidenced that the balance between formation upon CO 2 chemisorption and further hydrogenation of surface carbon intermediates is optimum for 2.5 wt. % Ru/CeO 2. For low metal contents, the CO 2 chemisorption is limited and no relevant, while as the metal content is increased, the hydrogenation of carbon species is less favourable. The 2.5 wt.% Ru/CeO 2 catalyst comprises a balance between surface-carbon groups formation and further hydrogenation. [Display omitted] [ABSTRACT FROM AUTHOR]

Honeycomb monoliths are the preferred supports in many industrial heterogeneous catalysis reactions, but current extrusion synthesis only allows obtaining parallel channels. Here, we demonstrate that 3D printing opens new design possibilities that outperform conventional catalysts. High performance carbon integral monoliths have been prepared with a complex network of interconnected channels and have been tested for carbon dioxide hydrogenation to methane after loading a Ni/CeO2 active phase. CO2 methanation rate is enhanced by 25% at 300 °C because the novel design forces turbulent flow into the channels network. The methodology and monoliths developed can be applied to other heterogeneous catalysis reactions, and open new synthesis options based on 3D printing to manufacture tailored heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

• Synergistic CuO – cryptomelane effect confers outstanding catalytic properties to Cu/CR catalyst with a higher molecular affinity to CO and O 2. • The enhanced reducibility in Cu/CR catalyst favors Cu+ interfacial sites, active in CO oxidation. • Oxygen vacancy refilling occurs mainly in bulky CuO particles aided by the support. • The correct balance between CuO and Cu+ sites in the 7% Cu/CR catalyst turns into the optimum CO-PROX catalytic performance. Nominally different Cu contents have been loaded on synthetic Cryptomelane oxide and the resulting CuO/Cryptomelane catalysts have been tested in the CO-PROX reaction. Catalytic activity was assessed in terms of the tunable synergistic interaction between copper and cryptomelane. This work entails the use of conventional characterization techniques such as XRD, Raman, FE-SEM, XPS with complementary DFT simulation. Additionally, it is reported for the first time, in-situ Work Function measurements of CO and O 2 interaction in CuO/Cryptomelane catalysts. Results reveal the strong influence of the interfacial properties on CuO/Cryptomelane reducibility, where Cu+ species are formed by means of redox interplay between Cu+2/Cu+ and Mn3+/ Mn4+. The optimal performance is achieved by the efficient participation of two active species: (1) Cu+ from an intimate MnO x contact, providing the active sites for CO oxidation; and (2) surface Cu+ species stabilized in CuO bulky particles for the efficient O 2 refilling. [ABSTRACT FROM AUTHOR]

[Display omitted] • The shape of a Ce 0.5 Pr 0.5 Ox soot combustion catalyst was tunned (Nanoparticles, NP, and macroporus, MS). • An hybrid-shape catalyst was prepared combining NP and MS. • The macropores of MS Ce 0.5 Pr 0.5 Ox are large enough to disperse Ce 0.5 Pr 0.5 Ox NP. • The hybrid catalyst decreased soot combustion by ca. 100 °C even after an aging process. • NP provide high activity and MS structure, high thermal stability and improved soot-catalyst contact. A Ce 0.5 Pr 0.5 Ox soot combustion catalyst has been shaped combining this material prepared in two different structures (nanoparticles and MS-macroporous) in a single active phase. Nanoparticles, prepared by reversed microemulsion method, provide high activity to the hybrid material, and the MS structure, obtained by a hard template synthesis method, provides high thermal stability and improved soot-catalyst contact. Ce 0.5 Pr 0.5 Ox nanoparticles present high surface area (148 m2/g; 5 nm) and improved redox properties with regard to other Ce 0.5 Pr 0.5 Ox structures, and the macropores size of MS Ce 0.5 Pr 0.5 Ox are large enough (around 100 nm) to properly disperse Ce 0.5 Pr 0.5 Ox nanoparticles inside and also to host soot particles, creating a high reactive catalyst environment. As a result, the as prepared Ce 0.5 Pr 0.5 Ox hybrid catalyst, mixed in loose-contact mode with soot, decreased soot combustion by ca. 100 °C with regard to the uncatalyzed reaction, and thermal aging at 800 °C only decreased this difference to ca. 75 °C. The as-prepared counterpart hybrid catalyst obtained dispersing pure ceria nanoparticles on pure ceria MS support was also active for soot combustion, but the activity was almost lost completely upon thermal aging due to ceria sintering. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon monoliths with tailored channel architecture and porosity were synthesized. • The PSD and macropore volume were controlled by varying the synthesis conditions. • Active-phase dispersion and gas diffusion through the carbon network were optimized. • The role that the monolith porosity plays in the catalytic performance was studied. • The potential of 3D printing to improve the catalytic supports is demonstrated. Sponge-like carbon monoliths with tailored channel architecture and porosity were prepared by combining sol–gel polymerization and 3D printing technology. The pore size distribution (PSD) and macropore volume were controlled by varying the water concentration used in the synthesis. The size and interconnection degree of primary particles, and consequently the pore width and macropores volume, increases by increasing the water concentration. However, a more heterogeneous PSD was detected at high water concentration, due to the better-defined spheres-like morphology of primary particles which leaves voids and corners between fused spheres together with bigger macropores leaves by the coral-like structure. The role of this porosity control on the CuO/CeO 2 catalytic performance was pointed out in the CO-PrOx reaction. The CuO/CeO 2 dispersion and distribution along the carbon network increases by increasing the water concentration, i.e. the pore width and macropore volume, enhancing the catalytic activity. However, this improvement is not observed at high water concentration in which preferential flow pathways are created favored by the heterogeneous PSD. This manifest that the porosity control plays an important role in the catalytic performance of monolithic catalysts and thus, the monolithic support must be specifically designed to optimize the catalytic performance of active phases for each application. [ABSTRACT FROM AUTHOR]

[Display omitted] • PrO x nanoparticles (10 nm; 81 m2/g) have been synthesized and tested in soot combustion. • Three morphological architectures were analysed: nanoparticles, 3DOM and uncontrolled structure. • PrO x nanoparticles reached the highest activity compared to other structured PRO x and CeO 2 catalysts. • PrO x nanoparticles kept high activity after aging at 800 °C. • CeO 2 catalysts suffer almost total deactivation upon aging. PrO x nanoparticles (10 nm; 81 m2/g) were synthesized and analysed as soot combustion catalyst in comparation with other reference materials including CeO 2 nanoparticles and PrO x and CeO 2 catalysts with three dimensionally ordered (3DOM) and without controlled structure. PrO x nanoparticles reached the highest activity; T50 decreases from 603 °C (uncatalysed combustion) to 494 °C. This high activity can be attributed to the high surface area/low crystal size, which enhances the soot catalyst contact, and to the improved reducibility. PrO x nanoparticles kept high activity (T50 = 520 °C) after aging at 800 °C, being significantly more active than aged PrO x catalysts with 3DOM and uncontrolled structure and also significantly more active than all aged CeO 2 catalysis which suffer almost total deactivation upon aging. In all cases, PrO x catalysts are more active than CeO 2 counterpart materials with the same structure and thermal history, and this applies to nanoparticles, 3DOM and uncontrolled structures. [ABSTRACT FROM AUTHOR]

• Increasing loading of Ni and Ru increases the surface basicity and forms new CO 2 adsorption sites. • High calcination temperature leads to an increase of RuO 2 particle size and formation of inert Ni species. • Ni/Al 2 O 3 catalysts present high metal-support interaction, so that only a relative amount of metal is active for CO 2 methanation. • Ru/Al 2 O 3 catalysts are more efficient than Ni/Al 2 O 3 in hydrogen dissociation; TOF of the former is about ten times than TOF of Ni catalysts. • Optimal behavior was found for 12% Ni and 4% Ru, which provide metal surfaces of 5.1 and 0.6 m2 g−1, respectively. The hydrogenation of CO 2 into CH 4 from H 2 produced by renewable energy is considered an interesting alternative in order to promote the development of such green energies. In the present work, the effect of Ni and Ru loadings on the catalytic performance of alumina-supported catalysts is studied for CO 2 methanation reaction. All catalysts were prepared by wetness incipient impregnation, characterized by several techniques (N 2 -physisorption, CO 2 -TPD, XRD, H 2 -chemisorption, XPS and H 2 -TPR) and evaluated for CO 2 methanation in a fixed bed reactor at GHSV = 10,000 h−1 and W / F C O 2 0 = 4.7 (g cat.) h mol−1. Characterization results showed that addition of increasing loadings of Ni and Ru lead to the formation of both CO 2 adsorption and H 2 dissociation active sites, which are necessary to carry out CO 2 hydrogenation into methane. Easily reducible ruthenium was dispersed on γ-Al 2 O 3 in form of large agglomerates, whereas Ni was better dispersed presenting a great interaction with the support. 12% Ni and 4% Ru resulted to be the optimal contents providing metal surfaces of 5.1 and 0.6 m2 g−1, T 50 values of 340 and 310 °C and activity being quite stable for 24 h-on-stream. In terms of turnover frequency (TOF), 4%Ru/Al 2 O 3 catalyst was quite more efficient than 12%Ni/Al 2 O 3 , probably due to a greater ability of ruthenium to dissociate hydrogen. The apparent activation energies for alumina supported Ni and Ru were 129 and 84 kJ mol−1, respectively. [ABSTRACT FROM AUTHOR]

CO 2 hydrogenation to CH 4 (or methanation) has been proposed to diminish CO 2 emissions producing a valuable fuel. A catalyst consisting of NiO-CeO 2 mixed oxide 6–7 nm nanoparticles with enhanced properties has been prepared, and compared with other NiO-CeO 2 reference catalysts including a mixed oxide with the same composition but without control of the size, a counterpart NiO-CeO 2 mixed oxide with three dimensionally ordered macroporous (3DOM) structure and an inverse catalyst consisting of bulk NiO-supported CeO 2 nanoparticles among others. At 275 °C the CO 2 methanation rate is near 3 times higher to that achieved with the counterpart reference catalyst prepared without control of the size, being more active than all reference catalysts. The selectivity towards CH 4 formation is ~100% in the whole range of temperature studied (until 500 °C), and kept the same activity and selectivity during a 25 h long-term test. The high activity of this catalyst is related with its high specific surface area (122 m2/g) and with the presence of highly-reducible Ni-O-Ce species on the nanoparticles surface • 6-7 nm NiO-CeO2 with enhanced activity for CO2 methanation has been prepared. • Reaction rate is 3 times higher to that of a catalyst prepared without size control. • Nanoparticles selectivity towards CH4 is near 100 % until 500 °C. • Nanoparticles kept the same activity and selectivity for 25 hours. [ABSTRACT FROM AUTHOR]