Determination of concentration of basic sites on oxides by IR spectroscopy.

As it is commonly known, CO2 reacts simultaneously with basic O2- and basic OH sites on oxides forming carbonates and bicarbonates, which can be followed by infrared spectroscopy (IR). However, here, we succeeded to elaborate experimental conditions under which CO2 reacted solely with O2- forming CO32- for ZrO2 and CeO2, and calculated the extinction coefficients of diagnostic bands of carbonate and bicarbonate species. For the first time, the developed IR method enabled the concentrations of O2- and basic OH for ZrO2, CeO2, Al2O3 and CuO to be measured separately. Moreover, in the case of all IR studied oxides, the sum of concentrations of O-2 and basic OH basic sites was comparable with the concentration determined by pulse adsorption of CO2. Thus, the presented extinction coefficients can be applied for IR basicity studies of various basic catalysts. We also followed the effect of thermal treatment on basicity of oxides.

Ethoxy Groups on ZrO2, CuO, CuO/ZrO2 Al2O3, Ga2O3, SiO2 and NiO: Formation and Reactivity.

The reaction of ethanol with surface OH groups on ZrO2, CuO/ZrO2, CuO, Al2O3, Ga2O3, NiO, and SiO2 was studied by IR spectroscopy. The basicity of oxides was followed by CO2 adsorption, and their ability to oxidize was investigated by H2-TPR. It has been found that ethanol reacts with surface OH groups forming ethoxy groups and water. Some oxides: ZrO2, CuO/ZrO2, Al2O3, and Ga2O3 contain several kinds of OH groups (terminal, bidentate, and tridentate) and terminal hydroxyls react with ethanol in the first order. Two kinds of ethoxyls are formed on these oxides: monodental and bidental ones. On the other hand, only one kind of ethoxy group is formed on CuO and NiO. The amount of ethoxy groups correlates with the basicity of oxides. The biggest amount of ethoxyls is produced on the most basic: ZrO2, CuO/ZrO2, and Al2O3, whereas the smallest amount of ethoxyls is produced on CuO, NiO, and Ga2O3, i.e., on oxides of lower basicity. SiO2 does not form ethoxy groups. Above 370 K ethoxy groups on CuO/ZrO2, CuO, and NiO are oxidized to acetate ions. The ability of oxides to oxidize ethoxyl groups increases in the order NiO < CuO < CuO/ZrO2. The temperature of the peak in the H2-TPR diagram decreases in the same order.

IR Studies of Ethoxy Groups on CeO2.

The reaction of ethanol with a surface of CeO2 was studied using IR spectroscopy. In some experiments, CeO2 was pretreated in a vacuum at 820 K which caused a partial reduction. In other experiments, CeO2 was reduced with hydrogen at 770 K. We also used CeO2 oxidized by oxygen treatment at 670 K. At low coverages, ethoxy groups and new surface OH groups were formed and water was not produced. On the other hand, at higher loading surfaces, Ce-OH was consumed and ethoxy groups and water were formed. Three kinds of ethoxyls were found on CeO2: monodentate, bidentate, and tridentate ones. They were characterized by various frequencies of symmetrical, asymmetrical, and combinational bands of C-C-O units. The reduction of CeO2 increased the contribution of tridentate ethoxyls and the oxidation increased the contribution of monodentate ones. At higher temperatures, ethoxy groups were oxidized to acetate ions with the formation of new surface OH groups. Monodentate ethoxyls were the most reactive and tridentate ones were the least reactive during oxidation. The amounts of acetate species were the highest for the oxidized CeO2.

Ethoxy Groups on ZrO2, CuO, and CuO/ZrO2 Studied by IR Spectroscopy.

The formation, properties, decomposition and reactions of ethoxy groups on ZrO2, CuO, and CuO/ZrO2 were followed by IR spectroscopy. The reaction of ethanol with terminal Zr-OH groups leads to the formation of monodendate ethoxy groups (type I), whereas the reaction of ethanol with tribridged Zr-OH grups results in the formation of bidendate ethoxyls (type II). In both cases, water is produced. Ethoxy groups of type II were also formed on CuO. The type of the surface species detected after interaction of ethanol with CuO/ZrO2 was the same as detected for both oxides (i.e., ZrO2 and CuO) separately. This suggests that no new phase was formed in the mixed oxide system. At higher temperatures, ethoxy groups were oxidized forming acetate ions. Gaseous ethanol present in the cell was oxidized to acetaldehyde without the intermediacy of ethoxy groups.

Modulation of ODH Propane Selectivity by Zeolite Support Desilication: Vanadium Species Anchored to Al-Rich Shell as Crucial Active Sites.

The commercially available zeolite HY and its desilicated analogue were subjected to a classical wet impregnation procedure with NH4VO3 to produce catalysts differentiated in acidic and redox properties. Various spectroscopic techniques (in situ probe molecules adsorption and time-resolved propane transformation FT-IR studies, XAS, 51V MAS NMR, and 2D COS UV-vis) were employed to study speciation, local coordination, and reducibility of the vanadium species introduced into the hierarchical faujasite zeolite. The acid-based redox properties of V centres were linked to catalytic activity in the oxidative dehydrogenation of propane. The modification of zeolite via caustic treatment is an effective method of adjusting its basicity-a parameter that plays an important role in the ODH process. The developed mesopore surface ensured the attachment of vanadium species to silanol groups and formation of isolated (SiO)2(HO)V=O and (SiO)3V=O sites or polymeric, highly dispersed forms located in the zeolite micropores. The higher basicity of HYdeSi, due to the presence of the Al-rich shell, aided the activation of the C-H bond leading to a higher selectivity to propene. Its polymerisation and coke formation were inhibited by the lower acid strength of the protonic sites in desilicated zeolite. The Al-rich shell was also beneficial for anchoring V species and thus their reducibility. The operando UV-vis experiments revealed higher reactivity of the bridging oxygens V-O-V over the oxo-group V=O. The (SiO)3V=O species were found to be ineffective in propane oxidation when temperature does not exceed 400 °C.

The Properties of Cu Ions in Zeolites CuY Studied by IR Spectroscopy.

The properties of both Cu2+ and Cu+ ions in zeolite CuY were followed with NO and CO as probe molecules. Cu2+ was found to be located in SII, SII*, and SIII sites, whereas Cu+ was found in SII and SII* sites. The fine analysis of the spectra of Cu2+-NO and Cu+-CO adducts suggests that both in SII and in SII* sites two kinds of Cu cations exist. They differ in the positive charge, which may be related to the varying numbers of AlO4- in close proximity. The experiments of NO and CO adsorption and desorption evidenced that both Cu2+ and Cu+ sites of highest positive charge bind probe molecules most strongly but activate them to a lesser extent than the Cu sites of lowest positive charge. The experiments of reduction with hydrogen evidenced that the Cu ions of higher positive charge are first reduced by hydrogen. On the other hand, Cu sites of the lowest positive charge are first oxidized by oxygen. The experiments with CuNaY zeolites of various Cu contents suggest that the first introduced Cu (at low Cu contents) created Cu+, which was the most neutralized by framework oxygens. Such Cu cations are the most stabilized by framework oxygens.

Substituted Phthalic Anhydrides from Biobased Furanics: A New Approach to Renewable Aromatics.

A novel route for the production of renewable aromatic chemicals, particularly substituted phthalic acid anhydrides, is presented. The classical two-step approach to furanics-derived aromatics via Diels-Alder (DA) aromatization has been modified into a three-step procedure to address the general issue of the reversible nature of the intermediate DA addition step. The new sequence involves DA addition, followed by a mild hydrogenation step to obtain a stable oxanorbornane intermediate in high yield and purity. Subsequent one-pot, liquid-phase dehydration and dehydrogenation of the hydrogenated adduct using a physical mixture of acidic zeolites or resins in combination with metal on a carbon support then allows aromatization with yields as high as 84 % of total aromatics under relatively mild conditions. The mechanism of the final aromatization reaction step unexpectedly involves a lactone as primary intermediate.