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Ethanol catalytic dehydration was studied on a γ-Al2O3 and Co-Al2O3 catalyst prepared by the strong electrostatic adsorption (SEA) method. Specific surface area characterization indicated that the Co-Al2O3 catalyst possessed higher surface area because of opening of γ-Al2O3 occluded pores. Acidity and basicity measurements of the catalysts by temperature programmed desorption (TPD) as followed by infrared and mass spectrometry (TPD-FTIR-MS) of adsorbed pyridine and CO 2, respectively, indicated that the Co-Al2O3 catalyst possessed about half the Lewis acidity (accessible to pyridine) and moderately higher basicity than the parent γ-Al2O3. However, similar acidity measurements by NH3-TPD suggested the presence of occluded micropore acidity inaccessible to pyridine. XRD and IR measurements indicated that the support in the Co-Al2O3 catalyst underwent partial nitridation forming aluminum nitride and nitrogen containing Co species due to the SEA synthesis conditions. It was found that the Co-Al 2O3 catalyst, under identical reaction conditions, could achieve similar ethanol conversion and ethylene selectivity to ethylene at lower temperatures than the original γ-Al2O3 support. Analysis of apparent activation energies contributions and water co-feeding tests indicated that the Co-Al2O3 was less inhibited by water and that water dimers and trimers were required to explain the experimental data. Furthermore, in situ modulation excitation-phase sensitive detection-diffuse reflectance infrared Fourier transform spectroscopy (ME-PSD-DRIFTS) during ethanol dehydration at reaction conditions confirmed the enhanced hydrophobic properties of the Co-Al2O3, making this catalyst less propense to water inhibition at low to moderate temperatures. The enhanced surface hydrophobicity in combination with new micropore acidity allowed more active sites for reaction not accessible in the parent γ-Al2O3. Additionally, evidence is also presented from in situ ME-PSD-DRIFTS for the participation of adsorbed ethanol and ethoxide species as well as terminal and bridging hydroxyls bonded to octahedral and tetrahedral Al on Al2O3 (1 0 0) and (1 1 0) facets as likely reaction intermediates in the conversion of ethanol to diethyl ether and ethylene.

UV–visible (UV–vis) spectroscopy is a common, powerful, and affordable technique for the characterization of heterogeneous catalysts. Here, we present an improved design of the commercial ubiquitous Harrick Scientific high temperature reaction cell for use in diffuse reflectance (DR) UV–vis spectroscopy with fiber optics at very close proximity of a catalyst sample and with high time resolution. The cell possesses significant dead volume which was reduced by a homemade compact dome and by volume reduction of cell void space with simple addition of glass beads, thereby, enabling faster transfer of gases. The cell was also improved by adding a second thermocouple to directly monitor the temperature of the catalyst bed via the outlet port without requiring any additional machining. This modified design and the use of an optical fiber DR probe in conjunction with a miniature concave-CCD combination based spectrometer allowed fast acquisition of in situ UV–vis spectra in the order of seconds and at temperatures up to about 500 °C. It is also shown that, unlike probes used in tubular reactors, expensive high temperature DR probes are not required in this design. The flow dynamics of the reaction setup were followed by an analysis of residence time distributions (RTD) via pulse experiments of Ar, O2, H2, CO, and CO2 as analyzed online by mass spectrometry (MS). These tests enabled a rigorous analysis of the fluid dynamics of the modified cell showing average gas residence times (after correcting for transfer lines and MS contributions) of ∼13 s at gas flow rates of 45 cm3/min (or ∼4 s at gas flow rates of 120 cm3/min) and a fluid behavior that could be approximately described by a CSTR reactor model. The RTD method is of general application and can be easily implemented to other reaction cells to rigorously determine gas mean residence times and distribution, regardless of setup and transfer lines design, provided that a reaction cell bypass line is added to the system. A thermal analysis indicated that significant heat losses due to radiation, conduction, and convection contribute to the observed sample bed vs heater temperature differences. Additionally, an example is presented to show the utility of the modified cell to monitor quickly (every 2 s) and continuously UV–vis spectra over an extended period of time during the in situ dynamic response of gold surface plasmon resonance (Au-SPR) peak shifts on a Au(1 wt%)/ZrO2 catalyst as it is exposed to controlled and cycling oxidizing and reducing environments. The results showed that the Au-SPR peak responded rapidly and shifted reversibly at the studied cyclic oxidizing and reducing conditions. The reported modifications of the reaction cell setup were shown to enable in situ spectroscopic characterization of heterogeneous catalysts. It proved useful for monitoring adsorption and desorption of gas species near gold nanoparticles via Au-SPR and for potentially tracking rapid changes (within seconds) on catalysts with characteristic finger prints in the UV–vis region.

The ketonization of various renewable biomass-derived oxygenated feedstocks such as carboxylic acids, aldehydes, alcohols, and esters is presented. As most previous ketonization reports focused on carboxylic acids, this overview extends the scope to homo-, cross-, and cyclo-ketonization of not only carboxylic acids (e.g., acetic, propionic, butyric, lactic, valeric, levulinic, dicarboxylic, and higher acids), but also of lesser reported aldehydes (e.g., acetaldehyde, propionaldehyde, and butyraldehyde), alcohols (e.g., ethanol, propanol, butanol, diols, and higher alcohols), and esters (e.g., small, intermediate, and large alkanoate chain length esters) aiming at obtaining more stable products, biofuels, and high-value chemicals. Ketonization of carboxylic acids (e.g., catalysts, mechanisms) is presented to provide the basis for understanding the ketonization of aldehydes, alcohols, and esters over metal oxides including ceria, titania, and zirconia, which have been the most active and studied catalysts for this reaction. Whenever possible, examples of ketonization of biomass-derived oxygenated compounds are presented to highlight the utility of the reaction and its practical application. As biomass product streams can contain a large number of different oxygenated compounds (e.g., more than 350 compounds in bio-oil), ketonization examples in the presence of more than one oxygenated molecule have also been considered.

Here we report an in situ UV–vis spectroscopy study of O2 and H2 adsorption on small gold nanoparticles supported on SiO2, Al2O3, ZrO2, ZnO, and TiO2 P-25 at high temperature which provides insights into gold adsorption and active sites. In situ gold surface plasmon resonance peak shifts from alternating and consecutive adsorption of O2 to H2 were correlated to relative charge transfer from/to gold via a Drude-Lorentz model considering contributions from free electrons and interband transitions. A novel methodology matching the relative charge transfer (from O2 and H2 adsorption at 398 K and flowing conditions) with Au surface site statistics derived from a truncated octahedron geometric model was used to provide strong in situ experimental and spectroscopic evidence for adsorption of O2 and H2 at the gold-support perimeter, which agrees with prior hypotheses for active site location from reactivity and theoretical studies. The prepared catalysts were also evaluated for CO oxidation at 398 K. The resulting TOFs normalized per different surface site location indicated that conversion rates were not limited by the density of sites at the gold-support perimeter, but primarily by the total gold surface sites, which were also further differentiated by the reducibility of the catalyst support.

The effects of catalyst composition on methanol and ethanol coupling reactions were studied on CuMgAlOx mixed metal oxides (MMOs). CuMgAlOx samples with Cu contents between 4 and 38 at.% were prepared by thermal decomposition of layered double hydroxides. These MMOs contained highly dispersed CuO consisting of isolated and oligomeric CuO (number of CuO nearest neighbors between 2 and 4.5) species as determined by ultraviolet–visible spectroscopy and temperature programmed reduction techniques. The catalysts were tested at 448–523 K, 0.1 MPa, alcohols gas-hourly space velocities (GHSVs) of 1000–3000 std cm3 gcat−1 h−1, and a feed MeOH/EtOH molar ratio of 4. Incorporation of Cu in MgAlOx solid solutions drastically changed product selectivity, formation rates, and catalyst stability. The main products on CuMgAlOx included C C coupling (e.g., C3+ alcohols, aldehydes, and esters), non-C C coupling (e.g., acetaldehyde, methyl formate, methyl acetate), and methanol decomposition (i.e., COx) products as a result of C C coupling reactions on M Al (M = Mg, Cu) and dehydrogenation, esterification, reverse methanol synthesis, and the water–gas shift reactions on Cu, respectively. The highest space-time yield of C C coupling products was 300 g kgcat−1 h−1, obtained with CuMgAlOx containing 21 at.% Cu at 523 K and an alcohols GHSV of 3000 std cm3 gcat−1 h−1. In situ Fourier transform infrared spectroscopy during MeOH + EtOH, EtOH, and MeOH reactions on CuMgAlOx and MgAlOx suggested that surface carboxylates (formate and acetate) are spectator species whereas oligomeric forms of formaldehyde and acetaldehyde may be responsible for the deactivation of MgAlOx.

Propylene epoxidation is an important reaction as propylene epoxide (PO) has a versatile application for synthesizing various industrially important compounds. Despite of high catalyst activity of Au/Ti–SiO2 catalyst after silylation, the catalyst deactivation, poor regeneration and more hydrogen conversion has put a major hurdle to optimize the catalyst performance in the commercial level. Addition of contaminant level trimethylamine (TMA) could improve the catalyst performance in terms of deactivation, regeneration and hydrogen conversion. In this study we have characterized silylated Au/Ti–SiO2 catalyst by in situ UV–vis–NIR, BET S.A, XPS and XAFS technique. The catalytic activity was checked for direct propylene epoxidation reaction in presence of trimethylamine (TMA). An explanation behind the reason of better performance of the catalyst after silylation was found in this study.

A series of Au/titanium silicalite-1 (TS-1) catalysts with different Si/Ti ratios and promoted with alkali and alkaline earth cations were prepared by deposition–precipitation (DP) and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity was highly dependent on the pH of the DP synthesis solution and the final composition of the catalyst. Addition of Group 1 metals such as K or Cs had little effect on the gold content, but increased activity, while Group 2 metals such as Mg, Ca, Sr, and Ba increased both the gold content and the catalytic activity. The highest improvement was provided by a Mg promoted catalyst, which at 443 K and 0.1 MPa with a H 2 /O 2 /C 3 H 6 /Ar = 1/1/1/7 feed mixture gave a propylene oxide (PO) formation rate of 88 gPO h −1 kg cat −1 , compared to 57 gPO h −1 kg cat −1 for an unpromoted catalyst, corresponding to a 50% enhancement of activity. Ammonia temperature-programmed desorption (NH 3 -TPD) measurements indicated little change in adsorption amount with promotion indicating that the yield increase was not due to the elimination of acidic sites on the catalyst. Instead, the improved catalytic performance was ascribed to increased Au capture efficiency and dispersion by the catalyst. The effect of Si/Ti ratio, pH of synthesis, and the promoter ions on the gold content could be understood from their effect on the surface charge of the support.

The selective oxidation of propane to acetone and 2-propanol with H 2 and O 2 was studied on Au/TS-1 by kinetic and spectroscopic analysis. A kinetic study using a factorial design at conditions where the catalyst was stable and gave propane conversions of 90%, resulted in a power-rate law expression of the form r oxyg. = k oxyg. (H 2 ) 0.74 (O 2 ) 0.36 (C 3 H 8 ) 0.29 . In situ Au L 3 -edge X-ray absorption near-edge spectroscopy (XANES) measurements showed activation of O 2 on Au, whereas in situ ultraviolet–visible (UV–vis) spectroscopy evidenced the presence of Ti-hydroperoxo species. The role of the Ti-hydroperoxo species was probed by a transient technique in which changes in Ti K -edge XANES spectra were used to determine the evolution of coverage with time ( d θ / d t ). It was shown that the rate of reaction by XANES ( 6.7 × 10 −4 s −1 ) was close to the turnover rate measured in a catalytic flow reactor ( 5.6 × 10 −4 s −1 ), indicating that the hydroperoxo species were true intermediates in the reaction. A proposed reaction sequence in which H 2 O 2 forms on Au sites and propane is partially oxidized on Ti centers accounts for the spectroscopic results and the reaction orders obtained experimentally for the power-rate law expression.

Propane epoxidation was carried out by sequential propane dehydrogenation–propylene epoxidation steps using a two-catalyst bed and H2 and O2 as the oxidant mixture. The propane dehydrogenation step used a Au/TiO2 catalyst that was active at the low temperature (443 K) used for the propylene epoxidation step; the latter used a Au/TS-1 catalyst. In situ Au L3-edge X-ray absorption near-edge structure and ultraviolet–visible measurements on Au/TiO2 under propane dehydrogenation conditions showed activation of oxygen on gold nanoparticles and evidence for the formation of adsorbed oxygen intermediate species responsible for the production of propylene. Propane epoxidation with H2 and O2 at 443 K and 0.1 MPa with the dual Au/TiO2 and Au/TS-1 catalysts resulted in an overall propane conversion of 2%, propylene selectivity of 57%, and propylene oxide selectivity of 8%, corresponding to a propylene oxide space-time yield of 4 g kg cat −1 h −1 . The catalysts showed little deactivation and maintained their conversion and selectivity levels for the 12 h duration of the measurements.

A catalyst consisting of gold supported on a Ti-containing silicate mesoporous material (TUD) with 13-nm pores was used for the epoxidation of propylene with mixtures of H 2 and O 2 . The catalyst activity was enhanced by the addition of a Ba promoter. The pH of deposition was important in controlling the gold loading and particle size. A pH of 7 gave a Au loading of 2.7 wt% and an average particle size of 2.0 nm, as determined by transmission electron microscopy, whereas a pH of 9 produced a much lower Au loading of 0.11 wt% and smaller particles of size about 0.9 nm, as estimated by X-ray absorption fine structure measurements. At 423 K and 0.1 MPa total pressure, the catalyst prepared at pH 7 gave a steady-state propylene conversion of 2.1%, a propylene oxide (PO) selectivity of 79%, and a H 2 efficiency of 3.8%, whereas that prepared at pH 9 gave a conversion of 1.4%, a PO selectivity of 99%, and a H 2 efficiency of 17%. The turnover frequency for PO production based on total gold increased on going to the sample prepared at pH 9. Thus, it is concluded that very small Au particles (about 1 nm) are the most active for epoxidation, whereas larger Au particles (about 2 nm) are less active because they promote direct H 2 oxidation to H 2 O. X-ray absorption near-edge spectroscopy results indicated that at reaction conditions, the small particles had partially oxidized gold but the larger particles had metallic gold, suggesting that the smaller particles had high coverage of oxygen or oxygen-derived species.

The kinetics of propylene oxidation to propylene oxide (PO) with H2/O2 mixtures on gold supported on the mesoporous titanium silicate, Ti-TUD, was investigated using Langmuir−Hinshelwood (L−H) models and power−rate law (PRL) models. The catalyst gave stable activity and was appropriate for the kinetic studies, giving high selectivity to PO (>95%) at low conversions of propylene (

It was found that silica-supported molybdenum oxide was high effective for the epoxidation of propylene among various silica-supported metal oxides. The post-catalytic bed volume played an important role in its formation. On a MoO x /SiO 2 with 0.255 mmol/g-SiO 2 , a propylene conversion of 17.6% and a PO selectivity of 43.6% were obtained at 5 atm, 573 K and flow rates of C 3 H 6 /O 2 /He = 10/5/10 cm 3 min −1 . The characterization studies indicated that crystalline MoO 3 nano-particle species was more effective for propylene epoxidation to PO than molecularly dispersed Mo oxide species. The reaction mechanism of propylene epoxidation on MoO x /SiO 2 catalysts is hypothesized to involve gas-phase radicals generated at relatively low temperature by the dispersed molybdenum oxide species. These radicals participated in homogeneous reactions with molecular oxygen to produce propylene oxide.

In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al2O3 and CaCO3 were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700 nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO3 catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56 wt.% supported on CaCO3 and promoted with 1 wt.% NaCl (Ag(56)–NaCl(1)/CaCO3). The catalysts were tested with reactant flow rates of C3H6:O2:He = 5:10:15 cm3 min−1, a gas hourly space velocity (GHSV) of 1800 h−1, a reaction pressure of 0.3 MPa, and a reaction temperature of 533 K (260 °C). Addition of 500 ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO3 catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO3 catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag+ species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO3 support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag+ species on the surface of the Ag(56)–NaCl(1)/CaCO3 catalyst could be the cause of a decline in PO selectivity observed during reaction.

In this study the effect of particle size on ethylene and propylene epoxidation was studied on a series of silver catalysts supported on CaCO 3 with loading levels of 0.5–56 wt%. Particle sizes determined from O 2 chemisorption uptakes at 443 K (170 °C) ranged from 50 to 660 nm, and this was confirmed by field emission scanning electron microscopy, which in addition showed crystallite agglomeration at high loadings. Reaction results show that large particles favor ethylene epoxidation by 3–5-fold at 473–493 K, whereas particle size does not have a large effect on propylene epoxidation. X-Ray diffraction measurements indicate that the bulk of the particles consist of silver in a metallic state, but in situ ultraviolet–visible (UV–vis) spectroscopy distinctly shows that in addition to a metallic component, small particles have silver in Ag + state. The small particles are probably covered by a layer of Ag 2 O, which results in lower selectivity for epoxidation for both propylene and ethylene oxidation in the small size regime. The approach to steady state is fast in propylene oxidation (3–4 h) and is accompanied by changes in the UV–vis spectra that indicate a reduction in the Ag 2 O phase. The approach to steady state is slow in ethylene oxidation (24–36 h) and is associated with changes in the UV–vis spectra that are consistent with the formation of a partially oxidized surface phase, which may involve subsurface or adsorbed oxygen.

In this paper, a theoretical method to estimate the textural properties of layered double hydroxides (LDHs) of the type [M2+1−xM3+x(OH)2][An−x/n] is presented. The theoretical calculations are based on the structure and composition of the LDH, using geometrical models of an LDH crystallite and the intercalating anion. Several examples of the application of this model to LDHs and pillared LDHs are shown. The estimated properties include the interpillar distances, the interlamellar and external areas, the interlamellar free volume, the fraction of external anions and the apparent and true density of the LDH. For well crystallized LDH samples, agreement between the estimated and the experimental results is found, for poorly crystalline samples, a correlation between the degree of crystallite agglomeration and the experimental areas is proposed.