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A generalizedapproach to determine the complete distribution ofmacropores, mesopores, and micropores from argon adsorption and mercuryporosimetry is developed and validated for advanced zeolite catalystswith hierarchically structured pore systems in powder and shaped forms.Rather than using a fragmented approach of simple overlays from individualtechniques, a unified approach that utilizes a kernel constructedfrom model isotherms and model intrusion curves is used to calculatethe complete pore size distribution and the total pore volume of thematerial. An added benefit of a single full-range pore size distributionis that the cumulative pore area and the area distribution are alsoobtained without the need for additional modeling. The resulting completepore size distribution and the kernel accurately model both the adsorptionisotherm and the mercury porosimetry. By bridging the data analysisof two primary characterization tools, this methodology fills an existinggap in the library of familiar methods for porosity assessment inthe design of materials with multilevel porosity for novel technologicalapplications. [ABSTRACT FROM AUTHOR]

Without techniques sensitive to complex pore architectures, synthetic efforts to enhance molecular transport in zeolite and other porous materials through hierarchical structuring lack descriptors for their rational design. The power of positron annihilation lifetime spectroscopy (PALS) to characterize the pore connectivity in hierarchical MFI zeolites is demonstrated, establishing a direct link with the enhanced catalyst lifetime in the conversion of methanol to valuable hydrocarbons. The unique ability to capture subtleties of the hierarchical structure originates from the dynamic nature of the ortho-positronium response to the pore network. The findings reveal the strong dependence on the way in which the hierarchical zeolites are manufactured, having direct implications for the practical realization of these advanced catalysts. [ABSTRACT FROM AUTHOR]

The determination of structure-performance relationships of ceria in heterogeneous reactions is enabled by the control of the crystal shape and morphology. Whereas the (100) surface, predominantly exposed in nanocubes, is optimal for CO oxidation, the (111) surface, prevalent in conventional polyhedral CeO2 particles, dominates in C2H2 hydrogenation. This result is attributed to the different oxygen vacancy chemistry on these facets. In contrast to oxidations, hydrogenations on CeO2 are favored over low-vacancy surfaces owing to the key role of oxygen on the stabilization of reactive intermediates. The catalytic behavior after ageing at high temperature confirms the inverse face sensitivity of the two reaction families. [ABSTRACT FROM AUTHOR]

The determination of structure-performance relationships of ceria in heterogeneous reactions is enabled by the control of the crystal shape and morphology. Whereas the (100) surface, predominantly exposed in nanocubes, is optimal for CO oxidation, the (111) surface, prevalent in conventional polyhedral CeO2 particles, dominates in C2H2 hydrogenation. This result is attributed to the different oxygen vacancy chemistry on these facets. In contrast to oxidations, hydrogenations on CeO2 are favored over low-vacancy surfaces owing to the key role of oxygen on the stabilization of reactive intermediates. The catalytic behavior after ageing at high temperature confirms the inverse face sensitivity of the two reaction families. [ABSTRACT FROM AUTHOR]

Herein, we report the preparation of small and narrowly distributed (2.1 ± 0.5 nm) Ag nanoparticles supported on passivated silica, where the surface OH groups are replaced by OSiMe3 functionalities. This synthetic method involves the grafting of silver(I) bis(trimethylsilyl)amide ([AgN(SiMe3)2]4) on silica partially dehydroxylated at 700 °C, followed by a thermal treatment of the grafted complex under H2. The catalytic performance of this material was investigated in the semi-hydrogenation of propyne and 1-hexyne and compared with that of 2.0 ± 0.3 nm Ag nanoparticles supported on silica. Whilst surface passivation slightly decreases the activity in both reactions (by a factor 2-3), probably as a result of the decreased alkyne adsorption properties or the presence of less accessible active sites on the passivated support, the AgNP@SiO2 catalysts demonstrate a remarkable selectivity for the production of alkenes. [ABSTRACT FROM AUTHOR]

Rutile TiO2 is a heavily investigated oxide with, to date, scarce applications in industrial catalysis. The inactivity of this material in oxidations has been related to its inability to dissociate molecular oxygen. Herein we show how rutile catalyzes the oxidation of HBr to Br2 through defect states that are introduced during the reaction. The identification of active, stable, and abundant materials for bromine production is key to the future implementation of Br2-mediated alkane functionalization processes. The catalytic properties of TiO2 are discussed in comparison to expensive rutile-type oxides, such as RuO2 and IrO2, on the basis of surface characterization and molecular modeling. [ABSTRACT FROM AUTHOR]

Rutile TiO2 is a heavily investigated oxide with, to date, scarce applications in industrial catalysis. The inactivity of this material in oxidations has been related to its inability to dissociate molecular oxygen. Herein we show how rutile catalyzes the oxidation of HBr to Br2 through defect states that are introduced during the reaction. The identification of active, stable, and abundant materials for bromine production is key to the future implementation of Br2-mediated alkane functionalization processes. The catalytic properties of TiO2 are discussed in comparison to expensive rutile-type oxides, such as RuO2 and IrO2, on the basis of surface characterization and molecular modeling. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mechanochemical treatment, a versatile tool for zeolite synthesis and modification. [•] Scalable, efficient, and mechanistically-distinct to solvent-intensive routes. [•] Structural transformations classified according to the energy required. [•] Catalytic properties enhanced by mechanochemical activation. [•] Rationalization will facilitate the scale up of future zeolite technologies. [ABSTRACT FROM AUTHOR]

CO 2 hydrogenation, green methanol, indium oxide, metal speciation, promotion Flame Spray Pyrolysis as a Synthesis Platform to Assess Metal Promotion in In2O3-Catalyzed CO2 Hydrogenation (Adv. Keywords: CO 2 hydrogenation; green methanol; indium oxide; metal speciation; promotion EN CO 2 hydrogenation green methanol indium oxide metal speciation promotion 1 1 1 04/18/22 20220414 NES 220414 B Flame Spray Pyrolysis b In article number 2103707, Núria López, Javier Pérez-Ramírez and co-workers apply flame spray pyrolysis as a standardized synthesis method to investigate promotional effects of nine transition metals in In SB 2 sb O SB 3 sb -catalyzed CO SB 2 sb hydrogenation to methanol, revealing that catalyst architecture (single atoms, clusters, and nanoparticles) and corresponding reactivity are dictated by the nature of the promoter. [Extracted from the article]

Highlights: [•] Alkyl lactates production is studied over gallium-modified FAU zeolites. [•] Alkaline-assisted galliation outperforms dry impregnation and ion exchange of Ga3+. [•] The method is successfully applied to MOR, MFI, FER, and BEA zeolites. [•] Galliated FAU is the best tin-free catalyst for C2–C4 alkyl lactates production. [•] Retained performance upon 5-fold increase in substrate feed concentration. [ABSTRACT FROM AUTHOR]

TiO2-, Al2O3-, and ZrO2-supported CeO2 catalysts with different Ce loadings were prepared by wet impregnation of the carriers with an acidified solution of cerium ammonium nitrate. The calcined catalysts were characterized by bulk and surface-sensitive techniques, which included microcalorimetry, and evaluated in the three-phase hydrogenation of alkynes under continuous-flow conditions at variable temperature (293-413 K) and pressure (1-90 bar). A number of acetylenic compounds, which contain terminal or internal triple bonds, conjugated unsaturations, and additional functionalities, were systematically assessed. The results revealed the full stereo- and chemoselective character of the ceria catalysts, which outperform the well-known Lindlar catalyst, and open promising perspectives for the revolutionary use of a cost-effective oxide for the production of olefinic compounds in the vitamin and fine chemical industries. [ABSTRACT FROM AUTHOR]

The principle of integral metal-organic framework (MOF) reconstruction is demonstrated for differently degraded HKUST-1 via a facile, one-step, solvent-assisted treatment. Controlled MOF degradation by exposure to 77% humidity, liquid water, and diluted hydrochloric acid produces a mixture of non-porous crystalline hybrid materials containing protonated linker and copper-oxo species, which are then reconstructed back into high-quality HKUST-1 by contacting them with ethanol. X-ray diffraction and sorption kinetics reveal a true memory effect of the system from completely degraded materials. The reconstruction approach is consequently extrapolated to gas- and liquid-phase treatments in a fixed-bed reactor with ethanol and ethanol/water mixtures for use in CO2 capture from a simulated pre-combustion gas stream. Up to a maximum of 94% porosity and 85% CO2 sorption capacity can be recovered from a steamed material. A degradation-reconstruction model is put forward based on X-ray diffraction observations and structural analyses, microscopy, N2 sorption, thermogravitry-mass spectrometry and IR spectroscopy observations, particularly elucidating the influence of various degradation pathways on the reconstruction. [ABSTRACT FROM AUTHOR]

Site modification and isolation through selective poisoning comprise an effective strategy to enhance the selectivity of palladium catalysts in the partial hydrogenation of triple bonds in acetylenic compounds. The recent emergence of supported hybrid materials matching the stereo- and chemoselectivity of the classical Lindlar catalyst holds promise to revolutionize palladium-catalyzed hydrogenations, and will benefit from an in-depth understanding of these new materials. In this work, we compare the performance of bare, lead-poisoned, and ligand-modified palladium catalysts in the hydrogenation of diverse alkynes. Catalytic tests, conducted in a continuous-flow three-phase reactor, coupled with theoretical calculations and characterization methods, enable elucidation of the structural origins of the observed selectivity patterns. Distinctions in the catalytic performance are correlated with the relative accessibility of the active site to the organic substrate, and with the adsorption configuration and strength, depending on the ensemble size and surface potentials. This explains the role of the ligand in the colloidally prepared catalysts in promoting superior performance in the hydrogenation of terminal and internal alkynes, and short-chain alkynols. In contrast, the greater accessibility of the active surface of the Pd-Pb alloy and the absence of polar groups are shown to be favorable in the conversion of alkynes containing long aliphatic chains and/or ketone groups. These findings provide detailed insights for the advanced design of supported nanostructured catalysts. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles are deposited on the surface of highly magnetic carbon-coated cobalt nanoparticles. In contrast to the established synthesis of Pd nanoparticles via reduction of Pd(II) precursors, the microwave decomposition of a Pd(0) source leads to a more efficient Pd deposition, resulting in a material with considerably higher activity in the hydrogenation of alkenes. Systematic variation of the Pd loading on the carbon-coated cobalt nanoparticle surface reveals a distinct trend to higher activities with decreased loading of Pd. The activity of the catalyst is further improved by the addition of 10 vol% Et2O to iso-propanol that is found to be the solvent of choice. With respect to activity (turnover frequencies up to 11 095 h−1), handling, recyclability through magnetic decantation, and leaching of Pd (≤6 ppm/cycle), this novel magnetic hybrid material compares favorably to conventional Pd/C or Pd@CNT catalysts. [ABSTRACT FROM AUTHOR]

Uranium oxide finely dispersed on ZrO2 crystals represents an effective and robust catalyst for the industrially relevant oxidation of HCl to chlorine. Remarkably, the catalytic performance increases significantly during the first 80 h on stream and remains stable thereafter. According to XRD results, this self-activation of the catalyst is accompanied by the disappearance of the starting α-U3O8 phase. The uranium distribution on the ZrO2 crystals at different stages of the reaction was visualized by aberration-corrected HAADF-STEM. The mostly mono-atomic uranium oxide layers present in the fresh catalyst broaden during reaction and often form a homogeneous coating over the support crystals comprising small uranium oxide species mostly comprising a single uranium atom. These species are found to be often located on top of columns of ZrO7 polyhedra, pointing to a strong fixation on the carrier. This observation likely explains the unique stability of the zirconia-supported uranium oxide catalyst in the Deacon reaction. [ABSTRACT FROM AUTHOR]

The aqueous-phase heterogeneously catalysed isomerisation of bio-oil derived glyoxal is herein introduced as a novel route for the sustainable production of glycolic acid. While commercial ultra-stable Y zeolites displayed only moderate performance, their evaluation enabled us to highlight the crucial role of Lewis acidity in the reaction. Gallium incorporation into these zeolites boosted the glycolic acid yield, although the best catalytic results were obtained over tin-containing MFI-type zeolites, reaching 91% yield of the desired product at full conversion. These materials comprised hydrothermally-synthesised Sn-MFI as well as a novel catalyst obtained by the introduction of tin into silicalite-1 by means of a simpler and more scalable method, i.e. alkaline-assisted metallation. In-depth spectroscopic characterisation of these systems uncovered a substantial similarity of the tin centres obtained by the top-down and bottom-up synthetic approaches. NMR spectroscopic studies gave evidence that the reaction follows a 1,2-hydride shift mechanism solely catalysed by Lewis-acid sites. The Sn-MFI analogue could be reused in 5 cycles without the need for intermediate calcination, did not evidence any tin leaching, and demonstrated suitability for utilisation under continuous-flow operation. The tin-based zeolites exhibited remarkable performance also in alcoholic solvents, leading to the one-pot production of relevant alkyl glycolates. [ABSTRACT FROM AUTHOR]

Galliation of USY zeolites in alkaline media creates tetracoordinated Lewis-acid centres linked to the framework which display outstanding selectivity in the isomerisation of dihydroxyacetone to ethyl lactate and full reusability. This simple and affordable post-synthetic route enables to tune the amount of Lewis acidity in the zeolite and has great potential for application in related biomass conversions. [ABSTRACT FROM AUTHOR]

Mass transfer in zeolite crystals can be enhanced by the introduction of a hierarchical network of auxiliary mesopores. To fully exploit pore engineering in the design of more efficient industrial catalysts, the benefit needs to be demonstrated over technically relevant forms. Here, the influence of shaping on the adsorption and diffusion properties of hierarchical ZSM‐5 is assessed by studying the gravimetric uptake of 2,2‐dimethylbutane over powders and millimeter‐sized bodies. Formed by extrusion or granulation with clay binders, the latter display a complex trimodal network of micro‐, meso‐, and macropores. The enhanced intracrystalline diffusivity due to the interconnected mesopores is preserved in the macroscopic bodies, independent of the shaping method or binder applied. Furthermore the superior overall diffusivity is retained in the hierarchical bodies compared to their conventional (purely microporous) counterparts, despite the significant extracrystalline resistance to mass transfer. The connective participation of mesopores, leading to a 6 times improved effective diffusivity in hierarchical with respect to conventional zeolite powders, is revealed by the distinct dependence on the adsorbate concentration and the relationship with the mesopore surface area. Analysis of the thermodynamic parameters derived from the adsorption isotherm proves a sensitive method to detect binder‐zeolite interactions induced upon shaping. [ABSTRACT FROM AUTHOR]

The conversion of layered metal hydroxides into a metal–organic framework is studied for the case of Fe–BTC (BTC = 1,3,5-benzenetricarboxylate). The synthesis occurs at room temperature as early as 5 min using a layered double hydroxide, green rust, as a precursor and yielding a product with high surface area. Monitoring of the Fe–BTC crystallisation kinetics as a function of the degree of crystallinity of the iron hydroxide reveals the dependence of MOF assembly on the presence of a layered structure in the precursor. Further insights into the evolution of the structure and Fe centers are provided by thermogravimetric analysis, infrared, Mössbauer and electron paramagnetic resonance spectroscopy. The obtained Fe–BTC exhibited a higher crystallinity and a higher content of accessible Lewis-acid sites compared to the commercial counterpart, which in turn resulted in a higher catalytic activity for Knoevenagel condensation. [ABSTRACT FROM AUTHOR]

The gas-phase partial hydrogenation of propyne was investigated over supported Ag nanoparticles (2-20 nm in diameter) prepared by using different deposition methods, activation conditions, loadings, and carriers. The excellent selectivities to propene attained over the catalysts, exceeding 90 %, are independent of the particle size but the activity is maximal over approximately 4.5 nm Ag particles. Certain kinetic fingerprints of Ag, such as the positive dependence on the alkyne pressure, the relatively low reaction order in H2, and the low apparent activation energy, deviate from those of conventional hydrogenation metals such as Pd and Ni, questioning the applicability of the classical Horiuti-Polanyi scheme. Periodic dispersion-corrected density functional theory (DFT-D) calculations and microkinetic analysis demonstrate the occurrence of an associative mechanism, which features the activation of H2 on the adsorbed propyne at structural step sites. By using the atomistic Wulff model, the number of B5 sites available on the Ag nanoparticles was estimated to be maximal in the size range of 3.5-4.7 nm. The rate of propene production correlates with the density of B5 sites, which suggests that the latter are potential active centers for the reaction. This alternative pathway broadens the mechanistic diversity of hydrogenation reactions over metal surfaces and opens new directions for understanding metals that do not readily activate H2. [ABSTRACT FROM AUTHOR]

Making a quick recovery: The widespread implementation of bromination reactions to manufacture value‐added products is contingent upon the development of sustainable and cost‐effective means to recycle copious amounts of HBr byproduct. We report families of heterogeneous catalysts for the full recovery of Br2 through HBr oxidation that display unprecedented low‐temperature activity and stability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hierarchization of ZSM-22 favors hydroisomerization and limits hydrocracking [•] Hierarchical ZSM-22 has lower acidity in micropores and higher acidity in pore mouths [•] Branching occurs in pore mouths; hydrocracking in pore mouths and micropores [•] Hierarchization is a unique tool to design superior hydroisomerization catalysts [•] Pristane is a convenient model molecule for probing pore mouth catalysis [Copyright &y& Elsevier]

Cuprous delafossites exhibit exceptionalelectrical, magnetic,optical, and catalytic properties. Through the application of a batteryof in situand ex situcharacterizationmethods complemented by density functional theory (DFT) calculations,we gathered an in-depth understanding of the synthesis of CuMO2(M = Al, Cr, Fe, Ga, Mn) by the solid-state reaction of Cu2O and M2O3and of their stability againstoxidative disproportionation to CuM2O4and CuO.TGA-DTA and XRD studies of the synthesis revealed that the natureof the M3+cation strongly impacts (i)the formation temperature of the delafossite phase, which occurredat a much lower temperature for CuCrO2than for the othermetals (1073 versus 1273–1423 K), (ii) themechanism of formation of the CuMO2in different atmospheres,which was found to comprise up to four steps in air and a single stepin N2, and (iii) the kinetics of the process,which could be significantly accelerated upon mechanochemical activationof the precursors by ball milling. The identification of unstableintermediate phases and, thus, a proper description of the synthesismechanism was only possible by the application of in situXRD. Electron microscopy, nitrogen sorption, and mercury porosimetryanalyses of the precursor oxide mixtures at different stages of thesynthesis in air revealed that particle agglomeration took place priorto the solid-state reactions forming the intermediate spinel phaseand the delafossite, respectively, and that these led to a substantialdrop in porosity and specific surface area. On the basis of XRD andHe pycnometry, the resulting CuMO2samples exhibit puredelafossite phase with rhombohedral structure (R3̅m), except for CuMnO2which features a monoclinicstructure (C2/m). Upon heating inair, CuCrO2retained its structure up to 1373 K, whileall other delafossites decomposed, CuAlO2at 1073 K, CuGaO2at 873 K, CuFeO2at 773 K, and CuMnO2at 673 K. The DFT-calculated surface phase diagram of CuCrO2and CuAlO2indicated that, at elevated oxygenpressures, the terminations with 1/2 and 0 ML of Cu are the most stablefor the (0001) facet. The formation enthalpy for interstitial oxygenspecies in the bulk is endothermic for both delafossites, while thatfor oxygen insertion in subsurface layers of these terminations isstill endothermic for CuCrO2but slightly exothermic forCuAlO2. These results provide an improved understandingof the chemistry of these mixed oxides, enabling their optimizationfor specific applications. [ABSTRACT FROM AUTHOR]

The manifestation of zeolite recrystallizationand the formationof amorphous aluminosilicate species during desilication are examinedto better understand the properties of alkaline-treated hierarchicalzeolites and their catalytic performance. This is achieved using asystematic experimental strategy, starting from treating the filtrateof alkaline-treated silicalite-1 in the presence of various externaladditives. No recrystallization is evidenced upon addition of tetrapropylammonium(TPA+) and/or aluminum hydroxide ions [Al(OH)4–], confirming the low probability of zeolite nucleationand/or growth during desilication. Conversely, ordered mesoporousmaterials (OMMs) form upon addition of cetyltrimethylammonium (CTA+) to the filtrate. By using other silicon sources, i.e., tetramethylorthosilicate or the organosilane dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium,we verify the facile formation of amorphous materials during alkalinetreatment of USY zeolites in the presence of hydrophobic micelle-formingalkyl moieties. A systematic characterization by X-ray diffraction,transmission electron microscopy, N2and Ar adsorption,inductively coupled plasma optical emission spectroscopy, and Fouriertransform infrared spectroscopy of pyridine adsorbed, demonstratesthat zeolites exposed to base solutions containing CTA+display weaker zeolitic properties, compared to those prepared usingTPA+, and should be considered as hierarchical zeolite/OMMcomposites. Catalytic tests in the alkylation of toluene with isopropylalcohol or benzyl alcohol evidence that CTA+-derived compositesdo not outperform the conventional USY zeolite. Only the hierarchicalUSY zeolite prepared by alkaline treatment in the presence of TPA+yielded a superior catalytic performance. [ABSTRACT FROM AUTHOR]

The article discusses a study which shows the stability of copper chromium oxide (CuCrO2), a copper-based catalyst with high hydrogen chloride (HCl), under oxidizing and chlorinating environments. It says that a novel CuCrO2-CeO2 composite for HCl oxidation has been developed. It concludes that the first copper-based CuCrO2 delafossite that has unique bulk chlorination resistance and allows stable chlorine production has been developed.

The article discusses the unique stability of delafossite copper chromium oxide (CuCrO2) during oxidation and chlorination. It presents a novel CuCrO2-cerium oxide (CeO2 composite for hydrogen chloride (HCl) oxidation to build on the result with fourfold activity. It states that in an equimolar mixture of copper oxide (Cu2O), single-phase cuprous delafossites were synthesized at 1273-1423 Kelvin (K) for 30 hours.

Hierarchical FAU- and LTA-type catalysts are prepared by post-synthetic modifications and evaluated in the base-catalyzed Knoevenagel condensation of benzaldehyde with malononitrile. A novel route to attain mesoporous Al-rich zeolites (A and X) is demonstrated, while mesoporous Y and USY zeolites are prepared using recently developed methods. Base functionality is introduced by alkali ion exchange (Cs, Na) or by high-temperature nitridation in ammonia. A thorough characterization of the zeolites' structure, composition, porosity, morphology, and basicity demonstrates that the presence of a secondary mesopore network enhances the ion-exchange efficiency and the structural incorporation of nitrogen. The modified USY zeolites display twice the conversion, while the hierarchical A, X, and Y are up to 10 times more active based on the enhanced accessibility. These results demonstrate that the Knoevenagel condensation takes place predominately at the external surface, highlighting secondary porosity as a key criterion in the design of basic zeolite catalysts. [ABSTRACT FROM AUTHOR]

In their Communication, A. J. Saadun et al. study bimetallic systems of distinct composition and equivalent nanoparticle size, showing that the formation of dilute ruthenium alloys with iridium suppresses deactivating overhydrogenation or coking pathways observed on the respective monometallic systems. Bimetallic catalysts, hydrodebromination, iridium, nanoparticles, ruthenium Keywords: bimetallic catalysts; hydrodebromination; iridium; nanoparticles; ruthenium EN bimetallic catalysts hydrodebromination iridium nanoparticles ruthenium 1 1 1 01/25/22 20220121 NES 220121 B The Cover Feature b shows a bimetallic Ir-doped Ru nanoparticle supported on carbon with unprecedented selective and stable character in the hydrodebromination of dibromomethane to bromomethane. [Extracted from the article]

Hierarchical clinoptilolite and Lzeolites are prepared using optimizedtandem dealumination–desilication treatments. The main challengein the postsynthetic modification of these zeolites is the high Alcontent, requiring a tailored dealumination prior to the desilicationstep. For natural clinoptilolite, sequential acid treatments usingaqueous HCl solutions were applied, while for L a controlled dealuminationusing ammonium hexafluorosilicate is required. Subsequent desilicationby NaOH treatment yields mesopore surfaces of up to 4-fold (clinoptilolite,64 m2g–1; L, 135 m2g–1) relative to the parent zeolite (clinoptilolite,15 m2g–1; L, 45 m2g–1). A thorough characterization sheds light on thecomposition, crystallinity, porosity, morphology, coordination, andacidity of the modified clinoptilolite and L zeolites. It is elaboratedthat, besides the degree of dealumination, the resulting Al distributionis a critical precondition for the following mesopore formation bydesilication. Adsorption experiments of Cu2+and methyleneblue from aqueous solutions and the catalytic evaluation in alkylationsand Knoevenagel condensation evidence the superiority of the hierarchicalzeolites, as compared to their purely microporous counterparts. Finally,the postsynthetic routes for clinoptilolite and L are generalizedwith other recently reported modification strategies, and presentedin a comprehensive overview. [ABSTRACT FROM AUTHOR]

RuO2/SnO2-Al2O3 has been recently reported as an industrial catalyst for Cl2 production through HCl oxidation. The stabilizing role of the alumina binder in the material, essential for its durable performance, is elucidated here. Al2O3 prevents chlorination of the SnO2 carrier under relevant reaction conditions, whereas, in its absence, SnO2 losses exceed 80 wt % in very short times owing to volatilization as SnCl4. Characterization by using X-ray diffraction, temperature-programmed reduction with hydrogen, and high-resolution TEM indicates expansion of the cassiterite cell in the SnO2-Al2O3 composite with respect to pure SnO2, which suggests the insertion of certain Al species upon mechanochemical and thermal activation of the oxide mixture. 27Al magic-angle spinning NMR and X-ray photoelectron spectroscopy studies reveal that the pentahedrally coordinated Al3+ cations interact with SnO2, generating an electron-depleted region near the surface of SnO2 particles. This induces some acidic character in cassiterite, which possibly makes it inert toward HCl. Besides this electronic effect, the presence of thin porous amorphous alumina films, partly covering the SnO2 surface, can offer additional geometric protection of the support. Mechanical mixing followed by calcination is essential to attain stabilization, and maximized effects are achieved with a high-surface area alumina. Other oxides such as SiO2 are ineffective in preventing tin losses during HCl oxidation. The practical implications of these findings are very important. The metal loading (fourfold decrease) and, thus, the cost of the catalyst can be significantly lowered without compromising its long-term stability. [ABSTRACT FROM AUTHOR]

Abstract: In situ (operando) investigations aim at establishing structure-function and/or coverage-reactivity correlations. Herein, we investigated the gas-phase HCl oxidation (4HCl+O2 →2Cl2 +2H2O) over ceria. Despite its remarkable performance, under low oxygen over-stoichiometry, this oxide is prone to a certain extent to subsurface/bulk chlorination, which leads to deactivation. In situ Prompt Gamma Activation Analysis (PGAA) studies evidenced that the chlorination rate is independent of the pre-chlorination degree but increases at lower oxygen over-stoichiometry, while dechlorination is effective in oxygen-rich feeds, and its rate is higher for a more extensively pre-chlorinated ceria. Even bulk CeCl3 could be transformed into CeO2 under oxygen excess. Electron Paramagnetic Resonance experiments strongly suggested that oxygen activation is inhibited by a high surface chlorination degree. The coverages of most abundant surface intermediates, OH and Cl, were monitored by in situ infrared spectroscopy and PGAA under various conditions. Higher temperature and p(O2) led to enhanced OH coverage, reduced Cl coverage, and increased reactivity. Variation of p(HCl) gave rise to opposite correlations, while raising p(Cl2) did not induce any measurable increase in the Cl coverage, despite the strong inhibition of the reaction rate. The results indicate that only a small fraction of surface sites is actively involved in the reaction, and most of the surface species probed in the in situ observation are spectators. Therefore, when performing in situ steady-state experiments, a large set of variables should be considered to obtain accurate conclusions. [Copyright &y& Elsevier]

A major challenge in the implementation of laboratory-designed catalysts is the scale-up into technically relevant forms. Advanced characterization is essential to understand and optimize catalyst assembly and function in industrial reactors. This Article presents an integrated approach to visualizing millimetre-sized extrudates and granules of a hierarchical MFI-type zeolite, displaying trimodal networks of micropores (0.56 nm), intracrystalline mesopores (?10 nm) and macropores (?200-300 nm). As exemplified for the conversion of methanol to olefins, the hierarchical zeolite yields a superior performance compared to its conventional analogue. The combination of dedicated specimen preparation with state-of-the-art optical, X-ray and electron-based microscopic and tomographic techniques proves a powerful methodology to reveal otherwise inaccessible information regarding structural organization over the whole range of length scales. It is expected that these tools will play a crucial role in the rationalization of scale-up principles in catalyst development. [ABSTRACT FROM AUTHOR]

In heterogeneous catalysis, rates with Arrhenius-like temperature dependence are ubiquitous. Compensation phenomena, which arise from the linear correlation between the apparent activation energy and the logarithm of the apparent pre-exponential factor, are also common. Here, we study the origin of compensation and find a similar dependence on the rate-limiting surface coverage term for each Arrhenius parameter. This result is derived from an experimental determination of the surface coverage of oxygen and chlorine species using temporal analysis of products and prompt gamma activation analysis during HCl oxidation to Cl2 on a RuO2 catalyst. It is also substantiated by theory. We find that compensation phenomena appear when the effect on the apparent activation energy caused by changes in surface coverage is balanced out by the entropic configuration contributions of the surface. This result sets a new paradigm in understanding the interplay of compensation effects with the kinetics of heterogeneously catalysed processes. [ABSTRACT FROM AUTHOR]

Abstract: Co-feeding of two relevant by-products of methanol synthesis, viz. dimethyl ether and methyl formate, in CO+H2 and CO+CO2 +H2 streams was used as a strategy to gain understanding of the reaction over ternary Cu/ZnO/Al2O3 and binary Cu/ZnO, Cu/Al2O3, and ZnO/Al2O3 catalysts. While dimethyl ether does not participate in the process, the addition of methyl formate remarkably increases the MeOH production by its oxygen-assisted split into active intermediate species (CH3O⁎ and HCOO⁎). Specifically, a breakthrough role was assigned to ZnO as catalytic partner for methyl formate conversion to methanol, since even the Cu-free ZnO/Al2O3 sample shows a considerable MeOH yield on MeF co-feeding. Alternatively, in the Zn-free Cu/Al2O3 sample, the presence of carbon dioxide in the inlet mixture was crucial to activate the methyl formate conversion path, likely because CO2 provides readily available oxygen to the Cu surface. [Copyright &y& Elsevier]

We present 100 % selectivity to p-chloroaniline through the continuous gas-phase (atmospheric pressure; T=393-523 K) catalytic hydrogenation of p-chloronitrobenzene over an activated CuAl (molar Cu/Al ratio 3:1) hydrotalcite. The synthesis by continuous co-precipitation and application of a CuNiAl (atomic Cu/Ni/Al ratio 2.75:0.25:1) catalyst is also described. Temperature-programmed reduction in hydrogen and XPS analyses of the ternary catalyst suggest CuNi interaction with no evidence of (bulk) alloy formation (based on XRD). Under the same reaction conditions, CuNiAl exhibited a higher (by up to a two-fold) hydrogenation rate when compared to CuAl, while the exclusive nitro-group reduction was maintained. [ABSTRACT FROM AUTHOR]

Abstract: Experimental and theoretical studies reveal performance descriptors and provide molecular-level understanding of HCl oxidation over CeO2. Steady-state kinetics and characterization indicate that CeO2 attains a significant activity level, which is associated with the presence of oxygen vacancies. Calcination of CeO2 at 1173K prior to reaction maximizes both the number of vacancies and the structural stability of the catalyst. X-ray diffraction and electron microscopy of samples exposed to reaction feeds with different O2/HClratios provide evidence that CeO2 does not suffer from bulk chlorination in O2-rich feeds (O2/HCl⩾ 0.75), while it does form chlorinated phases in stoichiometric or sub-stoichiometric feeds (O2/HCl⩽ 0.25). Quantitative analysis of the chlorine uptake by thermogravimetry and X-ray photoelectron spectroscopy indicates that chlorination under O2-rich conditions is limited to few surface and subsurface layers of CeO2 particles, in line with the high energy computed for the transfer of Cl from surface to subsurface positions. Exposure of chlorinated samples to a Deacon mixture with excess oxygen rapidly restores the original activity levels, highlighting the dynamic response of CeO2 outermost layers to feeds of different composition. Density functional theory simulations reveal that Cl activation from vacancy positions to surface Ce atoms is the most energy-demanding step, although chlorine–oxygen competition for the available active sites may render re-oxidation as the rate-determining step. The substantial and remarkably stable Cl2 production and the lower cost of CeO2 make it an attractive alternative to RuO2 for catalytic chlorine recycling in industry. [Copyright &y& Elsevier]

Abstract: The improvement of molecular transport properties of hierarchical H-ZSM-5 obtained by desilication was evidenced by studying the desorption of o-xylene and isooctane by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This technique enabled monitoring simultaneously bands associated with the molecular probes and the zeolite, using powdered sample masses as low as 1mg. Two H-ZSM-5 samples with markedly different crystal sizes were investigated. The first sample was commercial and consisted of small crystallites (ca. 250nm). The second sample were laboratory-made large crystals with coffin-like shape (ca. 17×4×4μm3). The hierarchical derivatives of the small and large zeolite crystals displayed 250 and 120m2 g−1 of mesopore surface area, respectively, in contrast to the 62 and 5m2 g−1 of the parent counterparts. The data based on o-xylene desorption were partly disguised by site-desorption limitations. Desorption experiments using isooctane evidenced a 4-fold reduction in the characteristic diffusion path length on both mesoporous small and large zeolites with respect to their purely microporous analogues. These results confirm the substantial potential for improvement of commercial nanocrystalline zeolites in diffusion-limited reactions upon the introduction of intra-crystalline mesoporosity by post-synthesis modification. [Copyright &y& Elsevier]

Abstract: Rationally designed RuO2-based Deacon catalysts can contribute to massive energy saving compared to the current electrolysis process in chemically recycling HCl to produce molecular chlorine. Here, we report on our integrated approach between state-of-the-art experiments and calculations. The aim is to understand industrial Deacon catalyst in its realistic surface state and to derive mechanistic insights into this sustainable reaction. We show that the practically relevant RuO2/SnO2 consists of two major RuO2 morphologies, namely 2–4 nm-sized particles and 1–3-ML-thick epitaxial RuO2 films attached to the SnO2 support particles. A large fraction of the small nanoparticles expose {110} and {101} facets, whereas the film grows with the same orientations, due to the preferential surface orientation of the rutile-type support. Steady-state Deacon kinetics indicate a medium-to-strong positive effect of the partial pressures of reactants and deep inhibition by both water and chlorine products. Temporal Analysis of Products and in situ Prompt Gamma Activation Analysis strongly suggest a Langmuir–Hinshelwood mechanism and that adsorbed Cl poisons the surface. Under relevant operation conditions, the reactivity is proportional to the coverage of a specific atomic oxygen species. On the extensively chlorinated surface that can be described as surface oxy-chloride, oxygen activation is the rate-determining step. DFT-based micro-kinetic modeling reproduced all experimental observations and additionally suggested that the reaction is structure sensitive. Out of the investigated models, the 2ML RuO2 film-covered SnO2 gives rise to significantly higher reactivity than the (101) surface, whereas the 1ML film seems to be inactive. [Copyright &y& Elsevier]

Abstract: We introduce a novel ‘spray deposition’ method as a continuous, reproducible, versatile, simple, and scalable method for the preparation of highly-dispersed, uniformly-sized, and sintering-resistant supported metal nanoparticles on porous supports. Instant drying of aqueous aerosol droplets containing the metal precursor (e.g. palladium nitrate) and the support (e.g. ferrierite zeolite) in a commercial bench-scale spray drier proves the key for maximizing the metal dispersion. In contrast, the much lower rates of solvent removal characteristic of dry and wet impregnation methods using classical drying or even freeze drying led to broad particle size distributions. The spray-dried Pd/ferrierite catalyst exhibited high alkene selectivity in the gas-phase hydrogenation of propyne. These results demonstrate that spray drying is not only a highly suited unit operation to prepare catalyst supports but also functional catalysts in one step. The method offers attractive opportunities for large-scale catalyst manufacture and as well as for preparation of well-defined systems for academic studies. [Copyright &y& Elsevier]

Abstract: The mechanisms of direct N2O decomposition and N2O reduction by H2 or NH3 on RuO2 has been studied by means of steady-state catalytic tests at ambient pressure, transient experiments in a temporal analysis of products (TAP) reactor, and density functional theory (DFT) simulations. Bulk RuO2 is very active for N2O decomposition into N2 and O2, achieving full conversion at 723K. According to the DFT calculations, coordinatively unsaturated ruthenium (Rucus) sites are active for the decomposition and oxygen elimination from the surface is rate-limiting step. When pre-reducing RuO2 with H2, the de-N2O activity in the low-temperature region increases. This is attributed to the higher reactivity of surface oxygen vacancies created by H2 at bridge sites compared to Rucus sites. Co-feeding of hydrogen or ammonia with nitrous oxide strongly accelerates the rate of N2O elimination. TAP studies show that oxygen species formed upon N2O decomposition over RuO2 react with NH3 and H2 yielding N2, NO, N2O, and H2O. Both TAP experiments and DFT simulations show that the N-containing intermediates coming from ammonia adsorb much stronger on the catalyst surface than H-containing intermediates coming from hydrogen. This causes blockage of active sites for N2O decomposition by the former species, accounting for the higher efficiency of H2 as reductant for N2O. The presence of O2 in the feed cancels the reducing effect of H2 or NH3 due to the more favorable re-oxidation of reduced RuO2 by O2 compared to N2O. [Copyright &y& Elsevier]

Abstract: Temporary supply of CO during propyne hydrogenation over a copper-based catalyst derived from a Cu–Al hydrotalcite permanently increased the alkene selectivity from 60% to 92% at 100% alkyne conversion (473K). The superior performance of the CO-modified copper catalyst (higher alkene selectivity and resistance against deactivation by fouling) was further confirmed at lower temperature (373K). Our catalytic results suggested that carbon monoxide in the presence of propyne and hydrogen irreversibly restructures the catalyst surface leading to a smaller copper ensemble that minimizes C–C coupling. Consequently, the enhanced alkene production in the CO-modified catalyst was coupled to a decreased oligomer production and very little propane production. The pretreatment mixture, feed CO concentration, and type of alkyne are important aspects to attain a selective copper catalyst. The CO effect in alkyne hydrogenation over copper radically differs from that over palladium or nickel. On the latter two metals, the increased alkene selectivity in the presence of CO is mostly due to a reduction in the over-hydrogenation channel. In addition, the effect is fully reversible, that is, it vanishes on removing CO from the feed. The permanent modification of the copper ensemble by CO might be advantageous for (chemo) selective hydrogenations of high acetylenic substrates. [Copyright &y& Elsevier]

Abstract: The oxidation of HCl to Cl2 (Deacon process) was studied over RuO2-based catalysts in bulk and supported forms. RuO2 (7wt.%) was incorporated onto different TiO2 carriers (rutile, anatase, and P25) by deposition–precipitation of Ru(OH)2 followed by calcination. RuO2/TiO2-rutile exhibits the highest activity at ambient pressure in a continuous flow fixed-bed reactor. Insights into the mechanism of this experimentally demanding reaction on RuO2 and the influence of the TiO2-rutile carrier were gained by studies in the Temporal Analysis of Products (TAP) reactor at 623K. HCl multipulsing in the absence of O2 leads to chlorination of the catalysts with no detectable gas-phase Cl2 production. The chlorine uptake of RuO2 amounts to 0.16mmolCl , which enables to estimate that ca. 75% of the total surface Ru atoms (coordinatively unsaturated and bridge sites) are chlorinated, forming a RuO2− x Cl x oxychloride. RuO2 is also chlorinated by Cl2, but to a lesser extent compared to HCl. The chlorine uptake of fresh RuO2/TiO2-rutile per gram of sample was four times higher than that of fresh RuO2, namely due to chlorination of the high surface area carrier. Upon equilibration at ambient pressure under Deacon conditions, the TAP-derived chlorine uptake in the supported catalyst experienced a 6-fold decrease with respect to the fresh sample due to permanent chlorination. Pulsing of a mixture of O2 and HCl over the catalysts revealed that both gas-phase Cl2 evolution and H2O desorption are impeded processes. Pump–probe experiments of O2 and HCl evidenced the tight dependence of the net Cl2 production on both the oxygen and chlorine coverage. In addition, a limited contribution of lattice surface species could be detected by the production of small amounts of Cl2 at very low coverages. The equilibration procedure (ambient or TAP conditions) influences the reaction mechanism and the net Cl2 production, giving account of the reaction complexity due to the highly dynamic state of the catalyst surface. The Deacon process on RuO2− x Cl x -based catalysts can be mostly described by a Langmuir–Hinshelwood scheme with a minor 2D Mars–van Krevelen contribution. [Copyright &y& Elsevier]

Abstract: Treatment of Mg–Al hydrotalcites (LDHs, layered double hydroxides) in aqueous (NH4)2CO3 at 298 K leads to composites of dawsonite, hydrotalcite, and magnesium ammonium carbonate. The mechanism and kinetics of this transformation, ultimately determining the relative amounts of these components in the composite, depend on the treatment time (from 1 h to 9 days), the Mg/Al ratio in the hydrotalcite (2-4), and on the starting layered double hydroxide (solid or delaminated form). The materials at various stages of the treatment were characterized by inductive coupled plasma-optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetry, and nitrogen adsorption at 77 K. The progressive transformation of hydrotalcite towards crystalline dawsonite and magnesium ammonium carbonate phases follows a dissolution–precipitation mechanism. A gradual decrease of the Mg/Al ratio in the resulting solids was observed in time due to magnesium leaching in the reacting medium. Dawsonite–hydrotalcite composite formation is favored at high aluminum contents in the starting hydrotalcite, while the formation of magnesium ammonium carbonate is favored at high Mg/Al ratios. The synthetic strategy comprising hydrotalcite delamination in formamide prior to aqueous (NH4)2CO3 treatment is more reactive towards composite formation than starting from the bulk solid hydrotalcite. [ABSTRACT FROM AUTHOR]

Abstract: Mechanistic and kinetic aspects of direct N2O decomposition over BaFeAl11O19 hexaaluminate were investigated in the Temporal Analysis of Products (TAP) reactor and compared with those previously determined for Fe-MFI zeolites. The catalysts were chosen due to their de-N2O operation in significantly different temperature regimes. Several micro-kinetic models were evaluated for describing the transient responses of N2O, N2, and O2 obtained in N2O pulse experiments at 823–973K. Thorough discrimination between these models enabled us to conclude that the preferred models of N2O decomposition over BaFeAl11O19 and Fe-MFI zeolites differ in the reaction pathways leading to O2 and N2. Gas-phase N2 and O2 are simultaneously formed over BaFeAl11O19 upon interaction of gas-phase N2O with a bi-atomic surface oxygen (*–O2) species. Contrarily, the formation of O2 over Fe-MFI occurs via a sequence of three elementary heterogeneous steps and limits the overall rate of N2O decomposition. Despite the easy O2 formation, BaFeAl11O19 is less active for N2O decomposition below 973K than the Fe-MFI zeolites due to the low coverage by *–O2. According to our quantitative micro-kinetic analysis, this species is formed when gas-phase N2O reacts with a mono-atomic oxygen (*–O) species. This reaction pathway is strongly influenced by the degree of isolation of iron species. The higher the degree of iron isolation in the catalyst, the lower the de-N2O activity. [ABSTRACT FROM AUTHOR]

Abstract: SO2 has been recognized as an effective reducing agent for N2O over iron-containing zeolite catalysts, lowering the operation temperature up to 100K with respect to the direct N2O decomposition. This unique behavior contrasts with the common poisoning effect of SO2 over other active de-N2O metals (e.g. Co, Cu, Rh, and Ru). The formation of surface sulfates has been generally posed as the main cause for catalyst deactivation by SO2. Through the use of in situ infrared spectroscopy (DRIFTS), we show that steam-activated FeZSM-5 indeed builds up stable sulfate species during the N2O+SO2 reaction. Significant amounts of sulfur were detected in the used catalyst by elemental analysis and X-ray photoelectron spectroscopy. However, the enhanced N2O conversion is remarkably stable, indicating that the reducing action by SO2 and the sulfation of the surface are decoupled. The resulting sulfate species are thus spectators in the catalytic process and do not block or alter the structure of the active sites for N2O reduction and decomposition. [Copyright &y& Elsevier]

Abstract: Desilication of ITQ-4 (IFR code, 1-dimensional 12-MR channel system of 0.62nm×0.72nm) in aqueous NaOH solutions was practiced in order to produce the zeolite in the hierarchical form, i.e. combining the native micropores with a secondary network of intracrystalline mesopores. The parent material (Si/Al=32) was synthesized using benzylquinuclidinium as the structure-directing agent in the presence of fluoride anions. The samples were characterized by ICP-OES, XRD, TEM, N2 adsorption, and FTIR spectroscopy. In a representative treatment, the mesopore surface area of the ITQ-4 experienced a sevenfold increase (from 29 to 206m2 g−1) upon optimized NaOH post-treatment, whereas the microporosity was reduced by 70% (from 0.20 to 0.06cm3 g−1). Chemical analysis and infrared spectroscopy of adsorbed pyridine showed that after alkaline treatment the amount of Brønsted acid sites remains practically constant whereas a significant increase in Lewis acid sites was obtained. Infrared studies with adsorbed 2,4,6-collidine concluded that the accessibility of acid sites in the hierarchical zeolite increased substantially due to an increase in the available active sites at the pore mouths of the hierarchical zeolite. [Copyright &y& Elsevier]

Abstract: As-synthesised and reconstructed NH4-Al-dawsonite and NH4-Ga-dawsonite, and the materials obtained by thermal treatment in the range 373–873K, were studied as heterogeneous catalysts for the epoxidation of cyclooctene with hydrogen peroxide at 353K and ambient pressure by means of High-Throughput Experimentation. The structural, morphological, and textural properties of the materials were investigated by elemental analysis, ICP-OES, XRD, FTIR, TEM, N2 adsorption, and TGA. The temperature at which the dawsonite precursors were treated proved to be crucial in determining the activity of the catalysts. The best catalyst identified in this work was obtained by calcination at 573K of reconstructed Ga-dawsonite. This material provides an epoxide yield of 51% and 99% selectivity after 4h at 353K. Remarkably, many of the catalysts derived from Al-dawsonite displayed an enhanced epoxidation activity upon recycling, reaching up to 30% epoxide yield with 98% selectivity over Al-dawsonite treated at 473K. [Copyright &y& Elsevier]

Abstract: Desilication in alkaline medium is demonstrated as a general route to synthesize hierarchical metallosilicate zeolite crystals with preserved crystallinity. The lattice trivalent cation (not only Al3+ but also Ga3+, Fe3+, and B3+) regulates the alkaline-assisted hydrolysis of silicon towards controlled mesoporosity development. This finding widens the family of modified zeolite compositions that integrate in a single crystalline material micropores and mesopores and enables better accessibility in catalytic applications compared to the purely microporous counterparts. [Copyright &y& Elsevier]