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The challenge of improving the activity of TiO

Developing functional materials from biomass is a significant research subject due to its unique structure, abundant availability, biodegradability and low cost. A series of chitosan–lignin (CL) composites were prepared through a hydrothermal method by varying the weight ratio of chitosan and lignin. Subsequently, these CL composites were combined with titania (T) to form a nanocomposite (T/CL) using sol–gel and hydrothermal based methods. T/CL nanocomposites exhibited improved photocatalytic performance in comparison with sol–gel and hydrothermally prepared pristine titania (SGH-TiO2), towards the selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (Bnald) under UV (375 nm) and visible light (515 nm). More specifically, the 75T/CL(25 : 75) nanocomposite (a representative photocatalyst from the 75T/CL nanocomposite series) showed very high selectivity (94%) towards Bnald at 55% BnOH conversion under UV light. Whereas, SGH-TiO2 titania exhibited much lower (68%) selectivity for Bnald at similar BnOH conversion. Moreover, the 75T/CL(25 : 75) nanocomposite also showed excellent Bnald selectivity (100%) at moderate BnOH conversion (19%) under visible light. Whereas, SGH-TiO2 did not show any activity for BnOH oxidation under visible light. XPS studies suggest that the visible light activity of the 75T/CL(25 : 75) nanocomposite is possibly related to the doping of nitrogen into titania from chitosan. However, according to UV-visible-DRS results, no direct evidence pertaining to the decrease in band-gap energy of titania was found upon coupling with the CL composite and the visible light activity was attributed to N-doping of titania. Overall, it was found that T/CL nanocomposites enhanced the photocatalytic performance of titania via improved light harvesting and higher selectivity through mediation of active radical species.

Exploration of the synergistic effect in catalysis upon simultaneous utilization of two sources of power, ultrasound and light, is barely explored and remains a challenging issue. A crucial reason behind this is the difficulty in designing and constructing a well-defined sonophotoreactor capable of taking advantage of the benefits of combining sonochemistry and photochemistry. Herein, we present our successful reactor and a detailed study regarding how the utilization of ultrasonication can act as a process intensification tool for selective and partial photooxidation of a biomass derived model compound, benzyl alcohol. The main outcome was the enhanced selectivity in the case of sonophotocatalysis compared to photocatalysis. This selectivity was ascribed to the effects derived from the cavitation phenomena, leading to phenomena such as hot spot formation and jetting. Our study can act as guidance towards understanding the unique effects of ultrasound irradiation as a hybrid process intensification method (HPIM) towards application in more complex chemical reactions and manipulation of the nanocatalysts’ photoreactivity in catalytic valorization applications.

Solar energy‐driven processes for biomass valorization are priority for the growing industrialized society. To address this challenge, efficient visible light‐active photocatalyst for the selective oxidation of biomass‐derived platform chemical is highly desirable. Herein, selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) was achieved by visible light‐driven photocatalysis over titania. Pristine titania is photocatalytically inactive under visible light, so an unconventional approach was employed for the visible light (λ=515 nm) sensitization of titania via a formation of a visible light‐absorbing complex of HMF (substrate) on the titania surface. Surface‐complexation of HMF on titania mediated ligand‐to‐metal charge transfer (LMCT) under visible light, which efficiently catalyzed the oxidation of HMF to DFF. A high DFF selectivity of 87 % was achieved with 59 % HMF conversion after 4 h of illumination. The apparent quantum yield obtained for DFF production was calculated to be 6.3 %. It was proposed that the dissociative interaction of hydroxyl groups of HMF and the titania surface is responsible for the surface‐complex formation. When the hydroxyl groups of titania were modified via surface‐fluorination or calcination the oxidation of HMF was inhibited under visible light, signifying that hydroxyl groups are decisive for photocatalytic activity., From ligand to metal: The selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) by visible light photocatalysis over titania is achieved with high DFF selectivity (87 %) at 59 % HMF conversion after 4 h of illumination. A complex of HMF on the titania surface acts as a sensitizer via a ligand‐to‐metal charge transfer (LMCT) under visible light.

The herein presented ultrasound-assisted ultra-wet (US-UWet) impregnation synthetic approach was followed in order to avoid the drawbacks of the conventional wet impregnation synthesis. The goal was to homogeneously decorate the surface of the TiO2 nanoparticles with nanometric sized (< 4 nm) clusters of mixed cupric and cuprous oxides. The physicochemical features of the nanocomposite (TiO2CuOx) were determined by high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and Diffuse reflectance (DR) spectroscopy. TiO2CuOx showed an enhanced and continuous capability to generate molecular hydrogen upon low power ultraviolet irradiation. The benchmark commercial TiO2 P25 did not reveal any H2 formation under these conditions. TiO2CuOx presented also a high efficiency for the additives-free selective partial oxidation of two well established biomass derived model platform chemicals/building blocks, 5-hydroxymethylfurfural (HMF) and benzyl alcohol (BnOH) to the value-added chemicals 2,5-diformylfuran (DFF) and benzyl aldehyde (PhCHO), respectively. The nanocomposite showed higher DFF and PhCHO yield compared to P25.

Sono- and photochemical reactions were combined in the synthesis of Pd-Fe- and Pt-Fe-doped titania-based photocatalysts supported on zeolite Y. In the applied procedure, no harmful reducing agents were used. The resulting photocatalysts were characterized using diffuse reflectance UV–vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), N 2 physisorption and inductively coupled plasma mass spectrometry (ICP-MS) techniques. The applied methodology leads to the formation of a mainly metallic form of platinum and oxidized forms of palladium and iron, with respect to different reduction potentials of metals. The photocatalytic degradation of phenol under UV light was applied as a test reaction. The photocatalyst containing Pt-Fe showed better results in this reaction in comparison with the Pd-Fe material, mainly because of the presence of the metallic form of platinum.

It has been demonstrated that sonophotodeposition can be one choice as a green method to synthesize bimetallic supported photocatalysts with enhanced performance for selective oxidations. A series of Pd–Cu supported on Titania-P90 photocatalysts were successfully prepared using this innovative method of effective synergistic combination of sonication and light. In addition, our method does not require the use of strong chemical reduction agent and it is executed in a short time, room temperature and atmospheric pressure. The prepared materials were characterized by a number of techniques such as High-Resolution Transmission Electron Microscopy (HRTEM), DR UV–vis spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and powder X-ray diffraction (XRD). Additionally, better bimetallic systems were obtained (methanol conversion >50% and selectivity to methyl formate >80%) by SonoPhotoDeposition (SPD) than in the case of the conventional photodeposition methodology. It has been discussed the possible reasons of the observed slight deactivation (8% after 2 h reaction test) of the best performing material in gas phase methanol selective photo-oxidation.

Commercial TiO2 (P25), alone or in the presence of graphite oxide (GO), was exposed to ultrasound treatment (US) with the objective to modify the surface of nanoparticles through introducing defects and chemical heterogeneity, and to build the composite with GO of synergistic features. The obtained materials were extensively characterized using XRD, HR-TEM, TA-MS, FTIR, XPS, potentiometric titration, adsorption of nitrogen, and UV/Vis diffuse reflectance techniques. The results showed that the US treatment/activation led to the formation of defects on the surface of the TiO2 nanoparticles, which were associated with an increase in the amount of terminal hydroxy groups, and which resulted in narrowing of the band gap energy. The composite formed upon the ultrasonic activation contained partially reduced GO particles deposited on the surface of TiO2 aggregates and bonded with the titania phase through its carboxylic groups existing at the edges of small defectous graphene particles, leading to a high volume of mesopores formed between the particles/aggregates of the nanoparticles. The US-treated materials showed a superior bifunctional detoxification performance, to adsorb and photocatalytically decompose vapors of a chemical warfare agent surrogate, as a result of the surface alteration/activation and an increase in the porosity.

The present paper reports on an innovative and simple route for the preparation of new hybrid materials based on TiO2 and carbonaceous supports with relatively high biochar content prepared via controlled laboratory batch pyrolysis system. Pine tar was used as a precursor for secondary char (confirmed by TGA) serving as a coating and “connecting material” between commercially available Degussa P25 TiO2 and biomass derived porous carbon support (biochar) produced from softwood or Lignin. The prepared hybrid materials were characterized by a series of physico-chemical characterization techniques such as XRD, XPS, TGA, UV–vis, XRF, SEM, COD and BET analysis. The results confirmed that the method used is viable and can be used to embed TiO2 in the structure of biochar. In aqueous phase phenol degradation, the TiO2/(secondary char-coated biochar) hybrid materials proved photocatalitically active, and especially the TiO2/secondary char-coated SWP700) showed better photocatalytic performance than the commercial TiO2 counterpart.

The aim of this work is to develop bimetallic Pd-Au/TiO2 P90 systems, which are highly active and selective for the photocatalytic oxidation of methanol to form methyl formate. Modification of commercial TiO2 P90 with Pd-Au nanoparticles was successfully achieved for the first time by means of a sonophotodeposition (SPD) method. The prepared materials were characterized by TEM, UV/Vis spectroscopy, X-ray photoelectron spectroscopy, and powder XRD. The Pd-Au bimetallic nanoparticles supported on titania exhibited remarkably enhanced catalytic activity in selective methanol oxidation to form methyl formate due to the synergism of Au and Pd particles, as well as the strong interaction between TiO2 and Pd-Au. SPD is a green methodology that can be used to prepare well-defined bimetallic surfaces on semiconductor supports with great promise for catalytic applications, in which selectivity can be tuned through adjustment of the surface composition.

In nuclear power plants, the concentration of hydrogen generated during the reaction of water with the zircaloy is diminished using the passive autocatalytic recombiners. Pd–Ni/Al\(_{2}\)O\(_{3}\) catalysts were tested in the recombination reaction and compared with the results for Pd/Al\(_{2}\)O\(_{3}\) and Pt/Al\(_{2}\)O\(_{3}\) catalysts. The catalytic reaction was performed in the flowing system under atmospheric pressure with a mixture of 0.5 % H\(_{2}\)-air in the stream in dry and wet conditions. The bimetallic, nickel-containing low-priced catalysts revealed a little lower activity than the high-priced Pd/Al\(_{2}\)O\(_{3}\), but their activity per active metal is promising. The lower atomic percentage of palladium in the active Pd–Ni phase resulted in higher turnover frequencies. Small amounts of water in the reaction mixture greatly decreased the catalytic performance but simple drying of the reaction mixture eliminated this effect.

Two series of highly dispersed supported Pd–Cu catalysts were prepared using different supports: highly acidic aluminum fluoride HS-AlF3, characterized by high surface area, and active carbon, both prepared by different preparation methods (fluorolytic sol–gel method and co-impregnation). A variety of techniques: chemisorption of hydrogen, XRD, TEM, and catalytic performance in two hydrogen-related probe reactions (in n-pentane hydroisomerization and CCl4 hydrodechlorination) were employed to probe metal dispersion and the extent of interaction between two metal components. A reasonable degree of bimetal intermixing in Pd–Cu/HS-AlF3 catalysts synthesized by fluorolytic co-gelation was recognized by the catalytic behavior in bifunctional hydroisomerization of n-pentane. A significantly decreased, compared to pure palladium, hydrogenation–dehydrogenation potential of Pd–Cu alloys led to a weaker performance of bimetallic catalysts. Similarly, it was found that incipient wetness co-impregnation of active carbon resulted in the formation of catalysts characterized by good metal dispersion and significant extent of Pd–Cu alloying. Although the monometallic 2 wt% Cu/carbon catalyst is nearly inactive in CCl4 hydrodechlorination, copper addition to palladium in the co-impregnated catalysts had very pronounced effect, vastly increasing the selectivity toward longer than methane hydrocarbons.

Formation of thin layers of photocatalyst in photo-microreactor is a challenging work considering the properties of both catalyst and the microchannel material. The deposition of semiconductor materials on fluoropolymer based microcapillary requires the use of economical methods which are also less energy dependent. The current work introduces a new method for depositing nanoparticles of TiO2 on the inner walls of a hexafluoropropylene tetrafluoroethylene microtube under mild conditions using ultrasound technique. During the ultrasonication process, changes in the polymer surface were observed and characterized using Attenuated Total Reflectance spectroscopy, Scanning Electron Microscopy and Confocal Microscopy. The rough patches form sites for catalyst deposition resulting in the formation of thin layer of TiO2 nanoparticles in the inner walls of the microtube. The photocatalytic activity of the TiO2 coated fluoropolymer based microcapillary was evaluated for removal of phenol present in water.

A series of new inorganic-organic hybrid materials based on TiO2 and new biochar-based supports (biochar obtained by pyrolysis of Miscanthus Straw Pellets (MSP) and Soft Wood Pellets (SWP) at 550 and 700 oC) were successfully prepared using ultrasound-assisted methodology. The resulting composites were characterized by a wide range physicochemical techniques and investigated in water and gas phase photocatalytic test reaction. Our best composite (TiO2/SWP700) achieved phenol degradation of 64.1% (under UV light) and 33.6% (under visible light). In addition, it also showed an extraordinarily high activity (~90 %) in selective oxidation of methanol to methyl formate in flow gas phase, high selectivity to methyl formate (~80 %) and high yield of methyl formate (~88 %) after 240 minutes of illumination. It can be noticed that when TiO2 is supported on biochar, presented a superior photocatalytic ability and could be recycled at least 5 times in both photocatalytic runs tests with reproducible high photocatalytic efficiency.

A new simultaneous combination of ultrasonication and ultraviolet irradiation was proposed to synthesize materials with photocatalytic properties. Different palladium modified TiO 2 systems were synthesized, using commercial TiO 2 P90 as a support. Morphological and surface characterization of the samples as well as photocatalytic activity for methanol photo-oxidation was studied. Among different characterization techniques X-ray diffraction, diffuse reflectance UV–vis spectroscopy, N 2 physisorption, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy with X-ray microanalysis (HRTEM-EDS) were applied. Degradation of methanol was studied in the gas phase. The results of this study demonstrate that palladium in the reduced form was obtained in sonophotodeposition method (SPD), although the calcination step at 300 °C in air flow during 4 h was the last in the synthesis procedure. All Pd modified photocatalysts obtained by SPD method were very active (>90%) in gas phase methanol degradation and highly selective (>80%) to CO 2 . The optimum palladium loading was fixed at 1 wt. %.

We report an operando XRD/MS experiment on nanocrystalline Pt supported on silica, monitoring quick growth of Pt in an NO atmosphere. XRD data following NO flow show structural changes typical of surface reconstruction. Although a small pressure of NO lifts surface reconstruction of a clean surface, a higher pressure of NO causes the surface to reconstruct again. TEM photographs show formation of clusters of Pt nanoparticles, pointing to growth controlled by coalescence. As surface reconstruction is the phenomenon that we always see accompanying quick growth, we postulate a mechanism of self-lifting cyclic reconstruction that drives the transport of whole clusters and their fusion.

Herein, we thoroughly investigate the role of the turbostratic structure, surface area and pore size of activated carbon supports on catalytic behaviour of 2 wt% Ni catalysts in aqueous phase hydrotreatment of drinking water contaminated by trichloroethylene (TCE) in batch and flow mode. Carbon materials with different physicochemical properties were obtained from the same parent amorphous material via the pretreatment procedure. Both carbons and Ni catalysts were characterized by BET, TPR, XRD, STEM, HRTEM, XAS and TPH on different stages of their biography. The studies showed the significant impact of turbostratic support structure as well as pore distribution on catalytic behaviour of nickel catalysts. Ni uniformly dispersed on mesoporous turbostratic carbon exhibited the highest efficiency in water purification. Additionally, we showed unique results of continuous flow water purification. Application of the flow mode plays the beneficial role in water hydrotreatment, which was proved for the two catalysts with negligible activity in batch mode. Our promising results open completely new perspectives in water purification.

International audience; HAlBEA zeolite is prepared by calcination of parent TEABEA zeolite at 823 K for 3 h in air following ionic exchange with NH4NO3 solution. NixHAlBEA zeolites are prepared by impregnation of HAlBEA with an aqueous solution of Ni(NO3)2, following a drying at 333 K to obtain NixHAlBEA. The calcination of HAlBEA and NixHAlBEA at 773 K for 3 h in air leads to the formation of C-HAlBEA and C–NixHAlBEA with appeared, for the latter, an octahedral and tetrahedral Ni(II) species incorporated in BEA framework as evidenced by XRD, DR UV–vis and XPS. Red-C-HAlBEA and red-C–NixHAlBEA are investigated as the catalysts in dehydrochlorination of 1,2-dichloroethane into vinyl chloride monomer in the presence of hydrogen at 503–523 K. Red-C-HAlBEA and red-C–Ni1.0HAlBEA show an excellent selectivity toward vinyl chloride (∼100%). Activity of HAlBEA and NixHAlBEA in the catalytic conversion of 1,2-dichloroethane strongly depends on the acidic properties of these materials and for the latter the catalytic activity depend on metal dispersion. The small Ni particles favor the dehydrochlorination of 1,2-dichloroethane to vinyl chloride. With increasing nickel particles size decreases activity of the red-C–NixHAlBEA catalysts. For these catalysts after kinetic run sintering of nickel phase is observed. Besides of carburization the nickel sintering is the main cause of red-C–NixHAlBEA deactivation. It is stronger for spent-red-C–Ni2.0HAlBEA with larger nickel particles than for red-C–Ni1.0HAlBEA containing smaller nickel particles (smaller than 5 nm).

The average size of the TiO2 nanoparticles was controlled at around 30 nm on Starbon 800 without using any surfactant, which is attributed to the hydrolysis and condensation (it is also proposed to be a plausible condensation with the carboxylate groups on the carbon surface) of the dissolved titanium(IV) isopropoxide into TiO2 by ultrasonic waves. As the Starbon in the composites has very good contact with the TiO2 nanoparticles (there is no Ti leaching after 240 min of photocatalysis, XRF analysis) it enhances the photo-electron conversion (better than Norit and graphene oxide carbons) of TiO2 by reducing the recombination of photo-generated electron–hole pairs. We have prepared an excellent new hybrid photocatalyst for aqueous phase phenol total mineralization.

Platinum and palladium supported on nanoscopic high surface area aluminum trifluoride (HS-AlF3) were prepared by the sol–gel synthesis. The properties of the HS-AlF3 support, catalyst precursors and catalysts were characterized by XRD, TEM, H2 chemisorption and FTIR-PAS of adsorbed pyridine. Both Pt/HS-AlF3 and Pd/HS-AlF3 catalysts were tested in the hydroconversion of n-pentane showing very good activity, stability and selectivity towards isomerization (80–90%) at 350 °C. The performance of catalysts was related to their bifunctional character. Very strong acidity of HS-AlF3 is the prerequisite for isomerization but the presence of metal is also essential to maintain a high conversion level.

Correction for ‘A novel biomass-based support (Starbon) for TiO2 hybrid photocatalysts: a versatile green tool for water purification’ by Juan Carlos Colmenares et al., RSC Adv., 2013, 3, 20186–20192.

The subjects of the research were barium-promoted ruthenium catalysts for ammonia synthesis supported on graphitized carbon. The purpose of this work was to study in detail the process of an active Ba–Ru/C catalyst formation. Another goal was to characterize the active state of the Ba promoter, that is the state corresponding to ammonia synthesis conditions. In situ XRD and TPR–MS techniques were applied to monitor the changes in the Ba–Ru/C specimens when heating in hydrogen (or H 2 + N 2 ) and H 2 + Ar mixtures, respectively. The post-activation state of the catalyst was characterized chemically via interaction of the reduced samples with water vapour at 50 °C and also via interaction with oxygen at 0 °C. The above mentioned experiments were supplemented with those of ammonia synthesis. It was shown that ruthenium facilitates decomposition of the promoter’s precursor (Ba(NO 3 ) 2 ) deposited onto the surface of Ru/C catalysts when heating the specimens in a hydrogen-containing stream. The Ba(NO 3 ) 2 /C reference materials, which do not contain ruthenium, are stable in a flowing H 2 + Ar mixture up to about 400 °C, whereas the Ba(NO 3 ) 2 decomposition starts at 100–120 °C in the Ba(NO 3 ) 2 –Ru/C systems (XRD, TPR–MS). The decomposition of Ba(NO 3 ) 2 in hydrogen leads to barium oxide (BaO) and metallic barium. Under steady-state conditions BaO is the only Ba-containing phase detected by the X-ray diffraction technique. Characterization of the post-activation catalysts showed that barium is partially reduced during the aforementioned operations and that these catalysts react with oxygen and water vapour. Based on the comparison of the O 2 consumption and H 2 evolution data one may deduce that the active form of the promoter is a mixture: Ba 0 + BaO. It can be stated that the temperature and content of the promoter (C Ba ) have a significant influence on NH 3 formation. The shape of reaction rate vs. barium content function is assumed to be an outcome of the promoter distribution on the active carbon surface and ruthenium surface. The trend of the integral reaction rate clearly reflects that of the Ru coverage by the barium-containing species, which is controlled by the heats of adsorption on ruthenium and carbon, respectively.

Pd/Nb 2 O 5 –Al 2 O 3 catalysts exhibited interesting properties in the hydrodechlorination of dichlorodifluoromethane. Introduction of niobia to alumina increases the selectivity for CH 2 F 2 , from ∼40% (for Pd/ Al 2 O 3 ) up to ∼75%, for similar metal dispersions. High-temperature reduction (773 K, HTR) of Pd/Nb 2 O 5 –Al 2 O 3 generates the SMSI state, understood as blocking the Pd surface by (partly) reduced niobia. The extent of SMSI effect is judged from a direct comparison between the performance of differently pretreated Pd/Nb 2 O 5 –Al 2 O 3 catalysts tested in n -hexane conversion (hydrogenolysis/isomerisation). After HTR of the niobia-containing Pd catalysts, the hydrodechlorination activity disappeared, however the SMSI state became reversed during hydrodechlorination. It is speculated that CCl 2 F 2 and liberated HCl, interact with NbO x decorants, converting them into volatile niobium oxychloride species.

Carboxylic acids were selectively reduced to aldehydes when their mixture with formic acid in the form of vapour had been passed over solid catalyst. The activities of 20 wt.% MO2/A catalysts, where M = Mn, Ce or Zr and A = Al2O3 have been studied in the mentioned reaction at the temperature range of 573–723 K. Hexanoic acid and its branched monomethyl and dimethyl isomers were used as substrates. For hexanoic acid reduction (HCOOH/C5H11COOH molar ratio 3) the following order of the maximum yield of aldehyde (in %) has been observed: Mn(58) > Ce(36) ≫ Zr(5) > support(1). Ketonization of an acid into undecan-6-one was the main side reaction in the upper range of reaction temperatures. Small amounts of hexan-1-ol and methyl hexanoate have also been detected among reaction products. An increase in the molar ratio of HCOOH/C5H11COOH diminished the ketone formation. The reactivity of branched x-methylpentanoic ( x = 2 , 3 and 4) acids in the reduction by formic acid depended strongly on the position of the substituent in the acid molecule and decreased in the following order: 4-methyl- > 3-methyl- > 2-methyl-. 2,2-Dimethyl- and 3,3-dimethylbutanoic acids were reduced to alkanals with very low yields (6%) even at the highest temperatures. The same order of reactivity of isomeric hexanoic acids has been observed in the homo-ketonization of pure acids. The MnO2/A catalyst has had a constant activity and selectivity in the reduction of hexanoic acid by formic acid. In the presence of HCOOH, methyl hexanoate was transferred below 673 K into hexanal and hexan-1-ol with 12 and 5% yields, respectively. Under the same conditions hexanal was reduced to hexan-1-ol with moderate yields (23%). Above 648 K, the ketonization of methyl hexanoate or hexanal took place and undecan-6-one was found to be the main product in both cases (94–96% at 723 K). It has been also shown that neither dihydrogen nor the products of the decomposition of formic acid can reduce hexanoic acid in the presence of the studied catalytic systems. The highest yields of hexanal (up to 3%) were reached at 673 K for the H2/C5H11COOH molar ratio equals 3. An increase in this ratio up to 15 resulted in an increase in the yield of hexanal up to 7%. A mechanism of the formation of an aldehyde in the reaction between formic and carboxylic acid has been proposed. It is assumed that a mixed formic-carboxylic anhydride is formed with its subsequent decarboxylation to an aldehyde. On the basis of XRD measurements of freshly prepared manganese catalyst, it was concluded that its active phase contains β -MnO2 which is almost quantitatively reduced to MnO in contact with either formic or hexanoic acid or their mixture.

We report an operando XRD/MS experiment on a nanocrystalline Pd(70%)Ag(30%) alloy supported on silica (10 wt% of metal) monitoring slow reversible Pd (in CO) and subsequently Ag (in He) surface segregation at 673 K. XRD data following CO and He flow show structural changes that can be modeled and interpreted in terms of the diffusion phenomena within a typical metal nanocluster. Qualitative differences in the rate of both segregation processes suggest different diffusion mechanisms as the Pd segregation involves vacancy depletion. The experimental details suggest that this kind of experiment can provide a very sensitive response to subtle changes at the surface of nanoclusters. Segregation processes can be stopped at any time by lowering the temperature below 573 K which allows engineering of the metal surface e.g. preparing for a catalytic low temperature reaction on a well-defined surface.

The 20 wt.% MO x /Al 2 O 3 catalysts, where M = Mn, Ce or Zr have been studied in ketonization of alkyl esters of heptanoic acid. A series of esters with the general formula C 6 H 13 COOR, where R = Me, Et, n -Pr, i -Pr, n -Bu, i -Bu, s -Bu and t -Bu, was used as substrates. At high conversions, manganese catalyst showed the highest selectivity. For heptanoates with primary and secondary alkyl groups the maximum yield of 7-tridecanone was observed in the 673–698 K temperature range. In the case of n -alkyl heptanoates the value of maximum yield increased with the elongation of the n -alkyl chain. The highest reactivity was observed for t -butyl heptanoate. In the presence of manganese catalyst, its quantitative conversion and the theoretical yield of 7-tridecanone were observed already at temperatures above 548 and 573 K, respectively. On the basis of XRD and TPR measurements of freshly prepared manganese catalyst, it was concluded that its active phase contains β -MnO 2 which is almost quantitatively reduced to MnO during contact with ethyl or t -butyl heptanoates. TPD measurements of ethyl and t -butyl heptanoates revealed dominant CO 2 desorption peak for both esters and lesser peaks for octan-2-one, heptanal, 1-heptanol and 7-tridecanone, and the substrates. Ethene, diethyl ether and ethanol, and 2-methylpropene were found to be desorbates for ethyl and t -butyl ester, respectively.

This work provides evidence that reduction of Pd/SiO 2 catalysts in dihydrogen at temperatures as low as 450 and 500 °C may already lead to a considerable interaction between palladium and silica, identified by the formation of palladium silicides (Pd 4 Si and Pd 3 Si). This result seems significant in view of the frequent usage of this temperature level in activation and pretreatment of Pd/SiO 2 catalysts. Application of a high flow of a reducing gas mixture and different reduction time periods indicates that an efficient removal of water vapor from the catalyst zone during hydrogen pretreatment facilitates reduction of silica to silicon, which, in turn, interacts with nearby palladium species. Silation of palladium in Pd/SiO 2 catalysts during a prolonged reduction at 450 and 500 °C has a considerable effect on the catalytic properties in the reaction of 2,2-dimethylbutane with dihydrogen. Incorporation of silicon into palladium lowers the catalytic activity, decreases the activation energy, increases the selectivity toward isomerization (at the expense of hydrogenolysis), and also changes the type of 2,2-dimethylbutane interaction with the surface of catalyst (from αγ to αγ ′ mode).

A comparable study of catalytic conversion of two C6-alkanes (n-hexane and 2,2-dimethybutane) has shown several analogies in the catalytic behavior of a series of differently loaded, chlorine-free Pd/Al2O3 catalysts. Different sample pretreatments have been used to modify the catalytic behavior. The catalytic performance of lowly reduced (at 573 K) samples of Pd/Al2O3 catalysts is similar to that exhibited by unsupported or silica-supported palladium, i.e. the predominance of metal-catalyzed reactions is observed with high hydrogenolysis selectivity and a bond-shift mode of isomerization. Highly reduced (at 873 K) samples experience a serious increase in overall activity, and simultaneously, big enhancement of isomerization selectivity (at ≤563 K), in agreement with previous reports [1] , [2] , [3] . At the same time, the activity is strongly correlated with the amount of activated alumina in the catalyst and only insignificantly dependent on Pd content in the catalyst. TPD of ammonia has been employed to confirm expected changes in the acidity generated by various catalyst pretreatments. It is considered that Lewis acidity of alumina, increased upon high temperature reduction (HTR), is a source of enhanced isomerization activity exhibited by Pd/Al2O3 catalysts. However, a palladium-free alumina cannot serve as efficient catalyst in alkane hydroconversion. Metallic function is needed to provide active hydrogen for a hydrogenative desorption of rearranged hydrocarbon species from acid sites of γ-Al2O3.

During reduction in dihydrogen at 873 K, a silica-supported palladium catalyst is initially converted to Pd4Si which further reacts with silicon-containing species to a Pd3Si phase. Such a stepwise phase change suggests that the mechanism of Pd silicide formation involves incorporation of silicon into a palladium phase, not vice versa, as was suggested in our previous work. This transformation has a great effect on catalytic properties of Pd–silica-containing systems in 2,2-dimethylpropane hydroconversion.

International audience; Influence of copper addition to nickel containing zeolite on activity and product selectivity in the hydrodechlorination of 1,2-dichloroethane was investigated. Ni2.0SiBEA and Cu2.0Ni2.0SiBEA zeolites were prepared by a two-steps postsynthesis method which consist of (1) creation of vacant T-atom sites by dealumination of calcined BEA zeolite with nitric acid and then (2) impregnation of as resulting SiBEA with aqueous nickel nitrate solution or co-impregnation with aqueous nickel and copper nitrate solution, respectively. Calcination at 773 K for 3 h in air and then reduction at 873 K over 3 h in flowing 10% H2/Ar of Ni2.0SiBEA and Cu2.0Ni2.0SiBEA, with an isolated pseudo-tetrahedral Ni(II) and Cu(II) species incorporated into BEA framework, leads to formation of red-C-Ni2.0SiBEA and red-C-Cu2.0Ni2.0SiBEA catalysts with very well dispersed metal nanoparticles. The state of nickel and copper in catalysts after calcination, reduction and reaction was characterized by XRD, low-temperature N2 sorption, TPR and XPS. The red-C-Ni2.0SiBEA and red-C-Cu2.0Ni2.0SiBEA catalysts were active in hydrodechlorination of 1,2-dichloroethane with very high selectivity into ethylene (90 and 96% respectively), desired product of this reaction. Thus, the simultaneous introduction of copper and nickel ions in SiBEA in the second step of postsynthesis procedure allows obtaining bimetallic red-C-Cu2.0Ni2.0SiBEA catalyst with well dispersed, separated Cu and Ni particles with higher selectivity toward ethylene than red-C-Ni2.0SiBEA catalyst. TEM experiments have shown that after catalytic run a very small agglomeration of metal particles took place. According to TPH and XPS measurements chlorine containing species are present in spent zeolite catalysts.

Ni 2.0 SiBEA and Ni 2.0 HAlBEA zeolites were prepared by two different procedures: (i) a two-step postsynthesis method that consist of (1) creation of vacant T-atom sites by dealumination of HAlBEA (Si/Al = 17) with nitric acid and then (2) impregnation of as resulting SiBEA (Si/Al > 1300) with aqueous nickel nitrate solution and (ii) conventional wet impregnation of HAlBEA (Si/Al = 17) respectively. The calcination of Ni 2.0 SiBEA and Ni 2.0 HAlBEA at 773 K for 3 h in air led to the formation of C-Ni 2.0 SiBEA and C-Ni 2.0 HAlBEA with appearance, for the former mainly pseudo-tetrahedral Ni(II) incorporated in BEA framework and for the latter, pseudo-tetrahedral and extra-framework octahedral Ni(II) as evidenced by XRD, DR UV–vis and XPS. After reduction at 873 K for 3 h in flowing 10% H 2 /Ar, red-C-Ni 2.0 SiBEA and red-C-Ni 2.0 HAlBEA were obtained and investigated as the catalysts in hydrodechlorination of 1,2-dichloroethane at 523–543 K. The activity of the catalysts carried out at atmospheric pressure depended on the reaction temperature, nature of nickel species present in C-Ni 2.0 SiBEA and C-Ni 2.0 HAlBEA, acidity of zeolites, distribution and size of nickel nanoparticles present in red-C-Ni 2.0 SiBEA and red-C-Ni 2.0 HAlBEA catalysts. Selectivity to desired product – ethylene was very high for red-C-Ni 2.0 SiBEA (∼90%) and low for red-C-Ni 2.0 HAlBEA (maximally 30%). The latter catalyst promoted strongly formation of vinyl chloride (up to ∼70%). We have shown that prepared by two-step postsynthesis procedure red-C-Ni 2.0 SiBEA was more resistant to sintering during hydrodechlorination of 1,2-dichloroethane than red-C-Ni 2.0 HAlBEA prepared by conventional wet impregnation.

Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect of various pretreatments of two chlorine‐free Pd/γ‐Al2O3 catalysts. The most important changes are observed when severely prereduced (at 600 °C) Pd/Al2O3 catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts, is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/γ‐Al2O3 catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of Pd after various pretreatments, as probed by temperature‐programmed hydride decomposition, can hardly be correlated with changes in the catalytic behaviour in the exchange reaction.

The effect of pretreatment conditions on the final metal dispersion and chemistry of precalcination of Pd/SiO 2 catalysts prepared from Pd(NH 3 ) 4 (NO 3 ) 2 and palladium acetylacetonate [Pd(acac) 2 ] have been studied. The fate of the Pd(NH 3 ) 4 2+ /SiO 2 precursor strongly depends on precalcination conditions. In helium, a vast majority of the ammine ligands desorb in a stepwise fashion, whereas considerable amounts of N 2 , N 2 O and NO are also liberated at various stages of precalcination in O 2 –He. The latter finding, not observed by others, is explicable by the known propensity of palladium to catalyse NH 3 oxidation. Pretreatment of the Pd(NH 3 ) 4 2+ /SiO 2 in He leads to well dispersed reduced Pd species, but an analogous pretreatment in O 2 –He results in the formation of an even more dispersed PdO species. In precalcination of the Pd(acac) 2 /SiO 2 precursor, an oxidizing atmosphere and temperatures 250 °C are essential for complete removal of carbonaceous species. After decomposition in He, the catalytic role of a carbonaceous material, retained by Pd/SiO 2 , depends on the temperature of the pretreatment. The low-temperature treatment (at 250 °C), followed by reduction in H 2 , supposedly leads to a loosely packed carbonaceous residue, leaving a considerable part of the palladium surface still capable of 2,2-dimethylpropane conversion. On the other hand, a high-temperature decomposition of the Pd(acac) 2 precursor (at 500 °C) in He greatly suppresses the activity. It is speculated that the decomposition in He at 500 °C leads to a carbide-like surface material, which is not eliminated by reduction in H 2 .