Reaction Of Propylene Oxide Research Articles

Tetranuclear Zn complex covalently immobilized on sulfopropylsilylated mesoporous silica: An efficient catalyst for ring opening reaction of epoxide with amine

Tetranuclear Zn complex, [Zn4(L)2(LH)2((CH3)2SO)2]·2CH3OH·(CH3)2SO·H2O (1) [where LH3 = 3-(E)-(2-hydroxyphenylimino)methyl-4-hydroxy-5-hydroxymethylphenyl (LH3)] was prepared and characterized by single-crystal X-ray analysis. Then, it was incorporated to the sulfopropylsilylated MCM-48, MCM-41 and SBA-15 mesoporous silica materials. The prepared materials were thoroughly characterized by XRD, FT-IR, N2 adsorption/desorption analysis, NH3-TPD, TGA, SEM-EDX and ICP-OES measurements. These catalysts were successfully used for the ring opening reaction of propylene oxide with morpholine producing the corresponding β-aminoalcohols. An abrupt increase in catalytic activities was observed after anchoring of the tetranuclear Zn complex onto the inner surface of sulfopropylsilylated mesoporous materials. Among all the catalysts, the tetranuclear Zn complex incorporated MCM-48 was found to be most active in this reaction system and gave maximum 95% conversion. Catalysis by the tetranuclear Zn complex immobilized on MCM-48 was totally heterogeneous and the catalyst was recyclable up to 4 times without leaching.

Synthesis of propylene glycol methyl ether catalyzed by imidazole polymer catalyst: Performance evaluation, kinetics study, and process simulation

An imidazole polymer (divinylbenzene-vinylimidazole) catalyst (P-DVB-VIM) was developed for production of the eco-friendly solvent propylene glycol methyl ether (PGME) by the propoxylation reaction of propylene oxide (PO) with methanol (ME). The catalyst was characterized in detail by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analysis. 1H NMR was used to characterize the structural features of the catalyst precursor, i.e., the linear polymer of vinylimidazole (PVIM). An “electrophile nucleophile dual activation” ring-opening mechanism was proposed based on the “cooperative effect” of the reactant and PVIM. The catalytic performance was investigated and optimized at 100–130 ℃ using an autoclave batch reactor. The results reveal that the P-DVB-VIM shows excellent catalytic performance, exhibiting the highest turnover frequency (TOF) number at 120 °C within 45 min. The reaction kinetics was systematically studied using the pseudohomogeneous (PH) kinetic model. The kinetic parameters were determined by non-linear regression analysis of the experimental data. Validation of the model showed that the experimental data were in good agreement with the predicted outcomes. Moreover, based on the proposed kinetic model, steady-state simulations of the production of PGME in a fixed-bed reactor were carried out to determine the optimal design parameters, thus providing a useful guide for the design and production of PGME on the industrial scale.

Reaction mechanism of propane oxidation over Co3O4 nanorods as rivals of platinum catalysts

Co3O4 nanorods and Pt/Al2O3 catalysts were synthesized and tested for catalytic oxidation of propane. In comparison to Pt/Al2O3, the catalytic results showed that Co3O4 nanorods were more active for propane oxidation under relatively high space velocity. Kinetic data suggested that the extraction of hydrogen from C-H bonds in propane can be considered as the reaction of kinetic relevance for both Co3O4 nanorods and Pt/Al2O3 catalysts. On both catalysts, propane could be first transformed into C3H7O* species. The intermediates further dissociate and are oxidized into carboxylates, with acetate and/or formate species as the primary products detectable by Fourier-transform infrared spectroscopy (FTIR). These species are later oxidized into CO2 and H2O as final products. However, the specific oxidation pathways might be different over these two catalysts. Over Co3O4 nanorods, propane oxidation appears to take place via the Langmuir-Hinshelwood mechanism. The rate-determining step is the C–H bond activation by the abstraction of H from adsorbed propane on two neighboring oxygen atoms. In contrast, on Pt/Al2O3 catalysts, the propane oxidation reaction follows an Eley-Rideal mechanism, and the rate-determining step is the activation of gaseous C3H8 on a neighboring oxygen atom and a vacant site.

Synthesis and structural characterization of methylindium imino/aminophenolates: Comparison to aluminum analogues and reactivity toward the coupling reactions of carbon dioxide with epoxides

We have synthesized methylindium complexes containing a variety of amino- and iminophenolate ligands for structural comparison to their aluminum analogues. The reaction of Me3In with the corresponding amino-/iminophenols resulted in the formation of MeIn(Et2NCH2CH2-abp) (1), MeIn(PyCH2-abp) (2), [MeIn(iPr-abp)]2 (3), MeIn(Ph-salen) (4), MeIn(Etsalan) (5), MeIn(Cy-ip) (6) and MeIn(Mes-ip) (7) [H2(Et2NCH2CH2-abp) = Et2NCH2CH2N(2-OH-3,5-C6H2tBu2)2, H2(PyCH2-abp) = (2-C5H4N)CH2N(2-OH-3,5- C6H2tBu2)2, H2(iPr-abp) = (CH3)2CHN(2-OH-3,5-C6H2tBu2)2, H2(Ph-salen) = 1,2-(NCH-2-OH-3,5-C6H2tBu2)2C6H4, H2(Et-salan) = 1,2-(NMeCH2-2-OH-3,5- C6H2tBu2)2C2H4, H(Cy-ip) = (2-OH-3,5-tBu2-C6H2)CHN(C6H11), and H(Mes-ip) = (2-OH-3,5-tBu2-C6H2CHN(2,4,6-Me3C6H2)]. X-ray crystallography studies show monomeric structures and five-coordinate indium centres for 1 and 2, a dimeric structure via intermolecular In⋯O interactions and fivecoordinate indium centres for 3, and monomeric structures and fourcoordinate indium centres for 6 and 7. DFT calculations were used to rationalize the observed dimeric structure of 3 and monomeric structures of 6 and 7, and gauge the effect of ligand steric bulk and atomic radius in indium versus aluminum on dimerization. Compounds 2 and 5 are active catalysts for coupling reactions of carbon dioxide and propylene oxide to yield propylene carbonate and carbon dioxide with cyclohexene oxide to yield polycyclohexene carbonate. This work provides insight into controlling intermolecular bonding and hence reactivity in indium and aluminum amino-/iminophenolate complexes, and represents one of the first examples of indium complexes as catalysts for the formation of cyclic- or polycarbonates from carbon dioxide and epoxides.

Gelatinization, pasting and retrogradation properties of hydroxypropylated normal wheat, waxy wheat, and waxy maize starches

Normal wheat starch (NWS), waxy wheat starch (WWS), and waxy maize starch (WMS) were hydroxypropylated with 3–9% propylene oxide (PO). The objectives of this study were to correlate morphology changes to pasting properties of hydroxypropylated starches and establish the relationship between molar substitution (MS) and degree of retrogradation of the hydroxypropylated starches. Gelatinization temperatures and enthalpy of the starches decreased after hydroxypropylation, and the extent of decrease was positively correlated to MS. Hydroxypropylation reduced retrogradation of the gelatinized starches during cold storage as determined by differential scanning calorimetry, but the effects varied among the starches. For the same level of PO (3 and 5%) reaction, hydroxypropylated WWS retrograded less than WMS. WWS and WMS had no retrogradation after reacted with 6% PO. However, a higher level of PO (9%) was needed to react with NWS, an amylose containing starch, to achieve no retrogradation. Hydroxypropylation promoted the swelling of the starch granules as observed by light microscopy, and Micro Visco-Amylograph results showed that hydroxypropylated starches had lower pasting temperatures and improved hot and cold viscosities.

Isotopic Oxygen Exchange Study to Unravel Noble Metal Oxide/Support Interactions: The Case of RuO2 and IrO2 Nanoparticles Supported on CeO2, TiO2 and YSZ

AbstractThe aim of this study is to unravel the mechanism of (noble metal oxide)/(active support) interactions for catalytic purposes. Hence, isotopic oxygen exchange (IOE) tests were performed on Iridium‐ and ruthenium‐based oxides supported on cerium oxide (CeO2), titanium oxide (TiO2), and yttria‐stabilized zirconia (YSZ). IOE tests demonstrated the metal oxide support involvement in the propane oxidation reaction, with YSZ‐based catalysts showing the highest exchange rate of oxygen, while CeO2 and TiO2‐based catalysts had a less diffusion of lattice oxygen in that order. This is related to the presence of extrinsic oxygen vacancies in the YSZ‐based catalysts and the reduction ability of the CeO2 and TiO2 supports. Despite the limitations on oxygen exchange in some of the noble/metal oxide catalysts, their catalytic performance was comparable to the ones that showed a high oxygen exchange. Therefore, active supports results in a higher engagement of oxygen from the support but not in a linear correlation with the catalytic performance of the metal/support.

A new coordination complex based on 2,2′-dipyridinium ligand as catalyst for the conversion of CO2 to propylene carbonate

Based on the ligand 2,2′-dipyridylamine (Hdpa) and di（2-pyrazyl）amine（Hdpza）, neutral molecular complexes [Co(Hdpa)2(NCS)2] (1) and [Co(Hdpza)2(NCS)2] (2) were synthesized. The DFT calculation of complex 1 was carried out to analyze the electron density distribution. Magnetic results indicate that a gradual decrease in χMT over the entire temperature range indicates strong zero-field splitting for the high-spin Co(II) ion in 1. The complex was used for the cycloaddition reaction of CO2 and propylene oxide, and compared with the reported complex 2 [Co(Hdpza)(NCS)2], the catalytic activity was 1 > 2. The Complex 1 exhibited excellent catalytic performance for converting CO2 into cyclic carbonates under mild conditions. For propylene oxide (PO) and CO2 synthesis of propylene carbonate (PC), the catalytic system showed a remarkable TOF as high as 5040 h−1.

The reaction of propylene to propylene-oxide on CeO2: An FTIR spectroscopy and temperature programmed desorption study.

The potential of CeO2 as an epoxidation catalyst is studied for the reaction of propylene with hydrogen peroxide (H2O2) by Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD). Adsorption and decomposition of H2O2 and propylene oxide (PO) are also explored to determine their surface chemistry and thermal stability. Hydrogen peroxide adsorbed dissociatively on CeO2 forming adsorbed peroxo (O-O) species, as observed through vibrational features at 890 cm-1 and (830-855) cm-1 (FTIR). The signal at 890 cm-1 disappeared when a pulse of propylene was passed through the catalyst, and at the same time, adsorbed PO was observed (a sharp IR mode at 827 cm-1; ring deformation). The reaction between gas phase propylene and adsorbed peroxide species suggested the Eley-Rideal type mechanism. The absence of a ring opening reaction of PO at room temperature may indicate that CeO2 can be a suitable oxide for epoxidation of hydrocarbons. PO started to decompose above 323 K, as observed from FTIR and TPD results. TPD spectra of PO show its desorption at 365 K, with a small fraction decomposing into acetaldehyde and formaldehyde due to partial decomposition, while CO2 and CO are released at higher temperatures. Adsorbed acetate, formate, and carbonate species, formed due to further reactions of aldehydes, are observed during the thermal reaction (FTIR).

Effect of cluster of quaternary ammonium ionic liquids on catalytic performance for CO2 fixation: ONIOM and MD

Formation of cluster is a popular phenomenon for ionic liquids due to the strong interactions between cation and anion. It would definitely affect the intrinsic properties of ionic liquids and its catalytic activity. Taken the coupling reaction of carbon dioxide and propylene oxide as an example, the effect of quaternary ammonium ionic liquids cluster on its catalytic performance is investigated by combination of ONIOM and molecular dynamics simulations, including quaternary ammonium ionic liquid, hydroxyl functionalized quaternary ammonium ionic liquid, protic quaternary ammonium ionic liquid, and protic hydroxyl functionalized quaternary ammonium ionic liquid. The influence of electrostatic interaction and covalent and non-covalent interactions on the catalytic activity is analyzed by natural bond orbital, electron localization function, and atoms in molecules to explore the critical factors to control the catalytic activity.

The Influence of water and catalyst leach process toward propane oxidation on MoVTeNb catalyst

The effect of the water stream to the propane oxidation on diluted MoVTeNb catalyst has been investigated. The present work has elucidated that careful operation of high throughput instrumentation can be used in various beneficial ways to speed up the discovery process of improved catalysts in other forms than enabling efficient trial-and-error testing of compositional variations of a given catalyst system. The result shows that the addition of massive amounts of water to the feed should have a negative influence on the kinetics, as water will compete with all other polar molecules in the system for adsorption sites. This work also investigated the effect of catalyst leach process toward propane oxidation. From the result, it can be described that catalyst leach process tends to reduce the phase of the catalyst that responds to the total oxidation of propane. This work also proposed the reaction network and gave the comparison between the propane oxidation reaction kinetic using leached and un-leached catalyst. The result showed that the activation energy of the acrylic acid formation on the leached catalyst was slightly higher than that of on un-leached catalyst. On the other hand, the activation energy of the carbon dioxide formation on the leached catalyst was much higher than that of on un-leached catalyst. It can be described that the leaching process to the catalyst can reduce the phase of the catalyst responsible for the total oxidation of propane.

A Density Functional Study of Amine Catalysts for CO2 Fixation into Cyclic Carbonates

The catalytic efficiency of three different kinds of amine groups for a prototype reaction of propylene oxide and carbon dioxide was investigated using density functional and energetic span model calculation. Our study demonstrated that tertiary amine groups perform best as catalyst at 100 °C and 10 bars because the corresponding catalytic cycle is free of any proton to be transferred around different molecular fragments. With primary or secondary amine catalysts, however, one or two protons at the nitrogen atom of amine can be transferred to the oxide oxygen, leading to intermediate structures stabilized by intramolecular hydrogen bonding at a deep valley in catalytic cycle. It is concluded that, when compared with the cases of primary or secondary amine groups, the effectiveness of tertiary amine group in catalysis originates from least hindrance to final products in catalytic cycle due to the absence of protons transferred.

Highly efficient synthesis of 1-methoxy-2-propanol using ionic liquid catalysts in a micro-tubular circulating reactor

The catalysis of ionic liquids (ILs) in the traditional stirred reactor suffers from insufficient mass and heat transfer, which always needs a long reaction time and results in a low reaction rate. In this work, highly efficient synthesis of 1-methoxy-2-propanol via the alcoholysis reaction of propylene oxide (PO) with methanol was proposed and achieved by the combination of micro-tubular circulating reactor with the IL [N4444][Buty] catalyst. Compared with the stirred reactor, the rate of alcoholysis reaction in a micro-tubular circulating reactor was found to be significantly improved. The reaction time was remarkably shortened to 20 min from 180 min as well as the yield of 1-methoxy-2-propanol reached 92%. Moreover, the kinetic study further demonstrated that the main reaction rate to 1-methoxy-2-propanol (K1) was about 20 times larger than the side reaction rate to byproduct 2-methoxy-1-propanol (K2) in the temperature range of 363–383 K. Such combination of micro-tubular circulating reactor with IL catalysts is believed to be a class of effective process intensification technique for highly efficient synthesis of 1-methoxy-2-propanol.

Physico-chemical investigation of catalytic oxidation sites in 4%Rh/CeO2 catalysts prepared by impregnation and deposition–precipitation methods

4 wt% Rh/CeO2 catalysts were prepared by two different methods: deposition–precipitation (DP) and impregnation (Imp). X-ray diffraction (XRD), differential scanning calorimetry and thermogravimetry (DSC-TG), temperature-programmed reduction (TPR), and electron paramagnetic resonance (EPR) were used for physicochemical characterization. The solids were tested in propylene and carbon black oxidation reactions. The 4%Rh/CeO2 (DP) showed better catalytic performance in both reactions compared to the catalyst prepared by the impregnation method. The XRD technique evidenced the formation of Rh2O3 phase in the DP-solid after calcination of this latter at 400 °C for 4 h. EPR evidenced, only in the DP-solid, the presence of O2− species in interaction with the CeO2 surface whereas Rh4+ ions in the form of clusters were identified in both solids. The TPR technique showed that the DP-solid was reduced by hydrogen at lower temperature compared to the impregnated one. The higher catalytic performance of the DP-solid was attributed to the presence of O2− species along with the presence of Rh2O3 phase in ceria and to the better reducibility and lower particle size of the rhodium species.

Identification and tuning of active sites in selected mixed metal oxide catalysts for cyclic carbonate synthesis from epoxides and CO2

The reaction of CO2 with epoxides to produce cyclic carbonate is one of the important transformations of CO2 which has commercial applications. In this study, several mixed metal oxides were explored as potential catalysts for CO2 cycloaddition reaction with epoxides. The catalytic activities of these catalysts were correlated with their physicochemical properties. It is found that the catalytic activity in terms of cyclic carbonate yield has a good correlation with the number of weak and medium acid-base sites irrespective of type of metal oxides used indicating that a combination of acidity and basicity is an important factor for this reaction. Among, different mixed metal oxides, Mn-Ba and Sn-Ni mixed metal oxides were found to be effective solid catalysts for the synthesis of cyclic carbonate from epoxide and CO2. These mixed metal oxides showed higher activity compared to individual oxides and physical mixture of respective metal oxides. Different compositions of mixed metal oxides and the effect of calcination temperature of the catalyst on cycloaddition of epoxide and CO2 were studied. Mn-Ba oxide and Sn-Ni oxide catalysts with metal ratios of 4.3:1 and 1.5:1 respectively, showed better activity compared to other compositions. The effect of various reaction parameters was studied to know the influence on the conversion and yield. Under optimized reaction conditions, Mn-Ba and Sn-Ni mixed oxides gave 96.0 and 90.2% yield respectively for propylene carbonate. Thus, mixed oxides were shown to be highly efficient catalysts with good recyclability for propylene oxide and CO2 reaction and also can be applied to some other epoxides effectively to make cyclic carbonates.

ZIF-8 as a Catalyst in Ethylene Oxide and Propylene Oxide Reaction with CO2 to Cyclic Organic Carbonates

CO2 is an important by-product in epoxides synthesis, accounting for 0.02% of worldwide greenhouse emissions. The CO2 cycloaddition to ethylene and propylene oxides is an important class of reactions due to the versatile nature of the corresponding organic carbonates as chemical feedstocks. We report that these reactions can be catalyzed by ZIF-8 (Zeolitic Imidazole Framework-8) in the absence of solvent or co-catalyst and in mild conditions (40 °C and 750 mbar). In situ infrared spectroscopy places the onset time for ethylene and propylene carbonate formation to 80 and 30 min, respectively. Although there is low catalytic activity, these findings suggest the possibility to cut the CO2 emissions from epoxides production through their direct conversion to these highly valuable chemical intermediates, eliminating de facto energetically demanding steps as the CO2 capture and storage.

Photocatalytic Abatement of Volatile Organic Compounds by TiO2 Nanoparticles Doped with Either Phosphorous or Zirconium.

The aim of this work is to study the activity of novel TiO2-based photocatalysts doped with either phosphorus or zirconium under a UV-Vis source. A set of mesoporous catalysts was prepared by the direct synthesis: TiO2_A and TiO2_B (titanium oxide synthesized by two different procedures), P-TiO2 and Zr-TiO2 (binary oxides with either nonmetal or metal into the TiO2 framework). Complementary characterizations (N2 physisorption at 77 K, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, X-ray Photoelectron Spectroscopy (XPS), and (DR)UV-Vis spectroscopy) were used to investigate the physicochemical properties of the prepared catalysts. Then, the photocatalysts were tested for the oxidation of propylene and ethylene under UV-Vis light. As a result, the most promising catalyst for both the propylene and ethylene oxidation reactions was the P-TiO2 (propylene conversion = 27.8% and ethylene conversion = 13%, TOS = 3 h), thus confirming the beneficial effect of P-doping into the TiO2 framework on the photocatalytic activity.

Hydroxypropyl and nanocrystal derivatives of white (Colocasia antiquorium) and red (Colocasia esculenta) cocoyam starches: functional, pasting, thermal and structural properties

Hydroxypropyl starch derivatives were prepared from the reaction of propylene oxide with the native starches of white and red cocoyam under alkaline conditions while starch nanocrystal derivatives were produced via acid hydrolysis method. The native starches and their hydroxypropyl derivatives were analyzed for functional behaviours, pasting properties, thermal properties, X-ray diffractometry and morphology while the starch nanocrystals were analyzed for solubility, X-ray diffractometry and morphology. Molar substitution values of the hydroxypropyl starch derivatives ranged between 0.23 and 0.26 and their degree of substitution ranged between 0.02 and 0.03. After derivation, the swelling power and water solubility of the native starches increased from 12.74 ± 0.02 to 21.36 ± 0.04 g/g (white cocoyam starch, WCS), 12.17 ± 0.04 to 18.06 ± 0.04 g/g (red cocoyam starch, RCS) and 11.61 ± 0.03 to 21.20 ± 0.06% (WCS), 12.21 ± 0.02 to 25.36 ± 0.05% (RCS) respectively. Except breakdown, all the pasting parameters (peak viscosity, hot paste viscosity, cold paste viscosity, setback, peak time and pasting temperature) significantly decreased (p < 0.05) as the levels of substitution increased. The gelatinization temperatures and peak height index reduced with an increase in substitution levels. Both native and hydroxyproylated starches exhibited CB-type X-ray patterns while the nanocrystals had V-type patterns. The starch nanocrystals formed precipitates with chloroform, but were practically insoluble in other solvents. The morphology of their microstructures revealed that the native starches were spherical and polygonal in shape while the nanocrystal starches appeared as aggregates. The starches studied could serve as alternative sources in meeting the ever-increasing demands of starch for food and non-food applications.

Effects of addition mode on Zn–Co double metal cyanide catalyst for synthesis of oligo(propylene‐carbonate) diols

Zn–Co double metal cyanide (DMC) complexes are promising catalytic systems for copolymerization of epoxide and CO2. In the work reported, Zn–Co DMC catalysts were prepared by parallel‐flow dropping, forward dropping and reverse dropping methods, aiming to provide an insight into the effect of addition mode on catalyst structure and catalytic performance. Catalytic properties were evaluated using the copolymerization reaction of propylene oxide (PO) and CO2 in the presence of chain transfer agent. The results indicated that the factors that affect crystalline state are different for different modes. And excess zinc chloride is the prerequisite for organic ligands to be retained in the catalyst and affect the structure. In addition, a catalyst with flower‐like morphology was obtained with the parallel‐flow dropping method which provided larger surface area. An appropriate O/Zn value ensured abundant active PO which would suppress the backbiting process by forming consecutive PO units adjacent to CO2 units. Oligo(propylene‐carbonate) diols with average molecular weight of 1020 g mol−1, CO2 incorporation of 24.92% and WPC of 5.14 wt% were obtained at 80 °C and 2 MPa.

Alkali and earth alkali modified CuOx/SiO2 catalysts for propylene partial oxidation: What determines the selectivity?

In this work, CuOx/SiO2 catalysts were investigated in the propylene partial oxidation reaction. Ordered mesoporous silica (KIT-6) was used to deposit 1–10 wt. % copper and subsequently modified with Na, K and Ca. The synthesized materials were characterized by N2 physisorption, XRD, TEM-EDS, CO2-TPD, operando UV/Vis DRS, operando XANES and pyridine DRIFT spectroscopy. Regardless of the CuOx loading, catalyst deactivation was observed during propylene oxidation reaction in non-modified catalysts, which was related to sintering of oligomeric [Cu-O-Cu]n species. Sintering of CuOx is strongly promoted under a reducing propylene atmosphere and related to the presence of Cu+1. The resulting bulk CuOx promotes acrolein selectivity. We produced modified catalysts with finely dispersed alkali metal cations, associated with the subnanometer CuOx phase, resulting in a greatly stabilized morphology and catalytic activity. Operando XANES analysis revealed that a substantial fraction of Cu2+ is transformed to Cu+ during the propylene oxidation reaction (52–68%, depending on the modifying atom). Also, the dynamics of reaching the quasi steady oxidation state differ strongly. The kinetics of oxygen abstraction and replenishment are substantially different, indicative of modified chemistry of the nucleophilic oxygen species, present in 5CuNa catalyst in contrast to others (5Cu and 5CuCa). We propose that Cu+ is not crucial for PO formation. Instead the electropositive Na+ and K+ decrease the nucleophilic strength of oxygen in CuOx, by attracting its electrons. Consequently, the catalytic action of oxygen changes from oxidative attack on the allylic hydrogen to oxygen insertion into the CC bond of propylene. This results in a noticeable selectivity shift from acrolein to propylene oxide. The effect of calcium on decreasing the nucleophilic character of O species in CuOx is negated by charge compensation by strongly adsorbed hydroxyl groups and Ca modification for PO selectivity is inefficient. Additionally we found, that further oxidation of propylene oxide is, most likely, the main factor determining high selectivity for COx products. The alkali modification which increases the PO selectivity does not function via elimination of LAS, but exclusively through attenuation of nucleophilic character of oxygen species.

EPR simulation to confirm the formation of Ag6O5 complex on the surface of 10% Ag/CeO2 catalyst after the propylene oxidation reaction

Ag2+(b) species were detected by electron paramagnetic resonance (EPR) on silver loaded over ceria by impregnation in a previous work. Contrasting the EPR simulation with the experimental measurements evidenced that, upon propene oxidation, the Ag2+(b) species transform into two clusters each containing 2 Ag2+ and 1 Ag+ species. This cluster is composed of two parallel electron spins (dimer) and three nuclear spins (trimer). Such a result led us to suggest that initially, Ag2+(b) species clusters were formed by three parallel electron spins. The ferromagnetic character of Ag2+(b) species may explain their catalytic performance towards total oxidation of propylene.