Effects of structural defects and acid–basic properties on the activity and selectivity of isopropanol decomposition on nanocrystallite sol–gel alumina catalyst

Catalytic nanomedicine: a brief review of bionanocatalysts

Catalytic nanomedicine is a research area and source of disruptive technology that studies the application of bionanocatalysts (organically functionalized mesoporous nanostructured materials with catalytic properties) in diverse areas such as disinfection, tissue regeneration in chronic wounds and oncology. This paper reviews the emergence of catalytic nanomedicine in 2006, its basic principles, main achievements and future perspectives, as well as giving a summary of the knowledge gaps that need to be addressed to exploit the full potential of this novel discipline. This review intends to foster knowledge dissemination regarding catalytic nanomedicine, and to encourage further research to elucidate the mechanisms and possible applications of these nanomaterials.

Hydride species on oxide catalysts

Hydride species on oxide catalysts are widely involved in oxide-catalyzed reactions, and relevant fundamental understanding is important to establish reaction mechanisms and structure-performance relations of oxide catalysts. In this topical review, recent progresses on the formation and reactivity of hydride species on the surface or in the bulk of oxides are briefly summarized. Firstly, characterization techniques for hydride species are introduced. Secondly, formation of hydride species on the surface or in the bulk of various oxides and their reactivity in oxide-catalyzed hydrogenation and dehydrogenation reactions are reviewed. Finally, short summary and outlook are given.

Vapor-phase oxidation of cyclohexane over supported Fe-Mn catalysts: in situ DRIFTS studies

Alumina-supported Fe-Mn oxide catalysts were synthesized by the incipient wetness impregnation method. The catalysts were characterized using various characterization techniques such as surface area, XRD, H2-TPR, and Raman spectral analysis. The adsorption (Cy-H, CO2) and oxidation of cyclohexane (Cy-H) were conducted by considering the in situ DRIFTS studies. The iron-impregnated catalyst possessed a higher surface area than the manganese-impregnated catalyst. The manganese-oxides remained dispersed in the support and the iron oxides remained in the crystalline phase in the catalyst 20Fe50Mn50/Al2O3. The reduction temperature of the catalyst decreased due to the synergistic effects of the iron-manganese oxides. The catalyst 20Fe50Mn50/Al2O3 was the most active for the vapor-phase oxidation of cyclohexane at 220 °C and 1 atm pressure. The cyclohexanolate, phenolate, and unidentate carbonate species were observed during the study. The lattice oxygen of the catalyst activates the C-H bond of cyclohexane for the formation of reactive-cyclohexanol, further decomposed by dehydration and dehydrogenation.

Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis

In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.

In Situ Friction-Induced Graphene Originating from Methanol at the Sliding Interface between the WC Self-Mated Tribo-Pair and Its Tribological Performance

Alcohols are reported to have superlubricity at low loads during sliding; however, their lubricity under high loads has rarely been reported. Meanwhile, the lubrication mechanism of alcohols under high loads is still not well understood. Here, we first report the lubricity of methanol under 98 N and 1450 rpm and demonstrate the formation of graphene and fullerene-like nanostructures induced by tribochemical reactions. Results show that the lubrication mechanism was mainly attributed to the friction-induced graphene under boundary lubrication condition. Besides that, the wear rate of a YG8 hard alloy ball mainly occurred at the run-in processes, and the friction-induced graphene effectively inhibited further wear after the run-in processes. The formation mechanism of graphene was well investigated, and the flash temperature rise and catalyst (WC, WO₂, and WO₃) were the major causes for the formation of graphene.

Sulfur-tolerant BaO/ZrO2/TiO2/Al2O3 quaternary mixed oxides for deNOX catalysis

A novel AZT – supported NSR/LNT catalyst with enhanced sulfur regeneration performance.

Evaluating and understanding the hydrothermal stability of alumina aerogel doped with yttrium oxide and used as a catalyst support for the thermo-catalytic cracking (TCC) process

The current work presents results concerning the hydrothermal stability of yttria-doped alumina aerogel, which was prepared by the sol–gel method using a supercritical drying technique. The influence of atmospheric steam at 750 and 1000 °C on the rate of sintering of yttria-doped alumina aerogel with various yttria contents was investigated. BET N2 adsorption measurements, X-ray diffraction, thermogravimetric analysis, FTIR of adsorbed pyridine, and 1H and 27Al MAS NMR were used for characterization of solid samples. It was found that the hydrothermal stability of yttria-doped alumina aerogel was greatly improved compared with alumina aerogel and conventional alumina. This was evident from the decrease in the loss of surface area and pore volume, and the minimization of structural transformations. These significant improvements were attributed to the combined effect of sol–gel method and the presence of yttrium ions. Yttria-doped alumina aerogel with various yttria loadings, when compared with undoped alumina aerogel, exhibited lower concentrations of surface –OH groups, higher amounts of bridged –OH groups, and lower degrees of crystallinity with smaller particle sizes. It was also observed that the thermal and hydrothermal stabilities of both yttria-impregnated alumina aerogel and conventional alumina were improved but to a much lower extent. These improvements were attributed to the presence of yttria, and subsequently the formation of surface yttrium aluminate. This structure was found to be more thermally stable than bare alumina owing to the presence of less surface defects and –OH groups. Therefore, it was concluded that to observe the most effective role of yttria, it is quite essential to incorporate it into the alumina structure via the sol–gel technique.Key words: thermo-catalytic cracking (TCC), yttria-doped alumina aerogel, yttria-impregnated alumina, hydrothermal stability, surface –OH groups, Lewis sites.

Characterization of various zinc oxide catalysts and their activity in the dehydration-dehydrogenation of isobutanol

Mono and bifunctional zinc oxide catalysts were prepared to study their activity in the catalytic conversion of isobutanol. The prepared catalysts were characterized by X-ray diffraction analysis and nitrogen adsorption measurements. The conversion of isobutanol was taken as a model reaction to measure the catalytic activity of the prepared oxide catalysts. The overall conversion yield of competitive dehydration-dehydrogenation reactions of isobutanol was found to be higher over the binary oxide catalysts than over the single oxide one at all reaction temperature within the range 250-400?C. The binary oxide catalysts were more selective for isobutene, as the predominant dehydrated product. The single oxide catalyst exhibited higher selectivity towards isobutyraldehyde as the dehydrogenated product, and the selectivity increased with increasing reaction temperature.

Adsorption of formaldehyde vapor by amine-functionalized mesoporous silica materials

The amine-functionalized mesoporous silica materials were prepared via the co-condensation reaction of tetraethoxysilane and three types of organoalkoxysilanes: 3-aminopropyl-trimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 3-(2-(2-aminoehtylamino)ethylamino) propyl-trimethoxysilane. Cetyltrimethylammonium bromide was used as a template for forming pores. Specific surface area and pore volume of the amine-functionalized mesoporous silica materials were determined using surface area and pore size analyzer. Fourier transform infrared (FTIR) spectroscope was employed for identifying the functional groups on pore surface. In addition, the amine-functionalized mesoporous silica materials were applied as adsorbents for adsorbing formaldehyde vapor. FTIR spectra showed the evidence of the reaction between formaldehyde molecules and amine groups on pore surface of adsorbents. The equilibrium data of formaldehyde adsorbed on the adsorbents were analyzed using the Langmuir, Freundlich and Temkin isotherm. The sample functionalized from n-(2-aminoethyl)-3-aminopropyltrimethoxysilane showed the highest adsorption capacity owing to its amine groups and the large pore diameter.

Aerogels: II. Applications in catalysis

Sol-gel synthesis, and the resulting materials (xerogels and aerogels) are finding increasing application in the synthesis of catalysts, due to their unique characteristics. The most important features of the sol-gel process are: the ability to achieve homogeneity at the molecular level, the introduction of several species in only one step and the ability to stabilize metastable phases. The supercritical drying process produces aerogels with structural features quite different to conventional materials. Some of these characteristics of aerogels can make them very effective catalysts.