Basic Hydroxyl Research Articles

Thermal Transformation of Caffeic Acid on the Nanoceria Surface Studied by Temperature Programmed Desorption Mass-Spectrometry, Thermogravimetric Analysis and FT–IR Spectroscopy

The studies of pyrolysis of caffeic acid (CA) and its surface complexes is important for the development of technologies of heterogeneous catalytic pyrolysis of plant- and wood- based renewable biomass components. In this work, the structure and thermal transformations of the surface complexes of CA on the surface of nanoceria were investigated using Fourier transform–infrared (FT–IR) spectroscopy, thermogravimetric analysis (TGA) and temperature-programmed desorption mass spectrometry (TPD MS). It was found that CA on the surface of cerium dioxide forms several types of complexes: bidentate carboxylates, monodentate carboxylates and complexes formed as a result of interaction with phenolic hydroxyl groups. This is due to the ability of nanosized cerium dioxide to generate basic hydroxyl groups that can deprotonate phenolic groups to form phenolates on the surface. The main pyrolysis products were identified. The possible ways of forming 3,4-dihydroxyphenylethylene, acetylene carboxylic acid, pyrocatechol and phenol from surface complexes of CA were suggested. It was established that on the nanoceria surface effectively occur the decarboxylation, decarbonylation, and dehydration reactions of the CA, which are the desirable processes in biomass conversion technologies.

New Insights into the Decomposition Behavior of NH4HSO4 on the SiO2-Decorated SCR Catalyst and Its Enhanced SO2-Resistant Ability.

This article illustrates the detailed decomposition behavior of NH4HSO4 on the TiO2 and TiO2–SiO2 supports, along with the effect of SiO2 addition on the sulfur resistance of the corresponding V2O5-based catalysts. For TiO2 support, sulfate species selectively occupied its surface basic hydroxyl groups, while Si–OH groups functioned as the main sites for the accommodation of NH4HSO4 over the TiO2–SiO2 mixed support, enabling its surface sulfate species with higher thermal stability. Compared with NH4+ on the TiO2 surface, NH4+ on the TiO2–SiO2 mixed support was much easier to be consumed during the heating process, hence causing some variations in the decomposition behavior of NH4HSO4. Finally, adding SiO2 enhanced the SO2 tolerance properties of the catalysts to a certain extent. When exposed to the SO2-containing flue gas, the deposition of NH4HSO4 mainly caused serious deactivation of SiO2-free catalyst, while the as-accumulated SO42– also contributed to the declined activity of SiO2-added catalyst. These results ensured the potential commercialization of TiO2–SiO2-based catalysts in the typical low-temperature selective catalytic reduction systems in the short run and pointed out a strategy to design new catalysts with superior activity and enhanced SO2-tolerant ability.

Surface acetone reactions on ZnxZryOz: A DRIFTS-MS study

We report a systematic DRIFTS-MS study of surface acetone aldolization and self-deoxygenation reactions on ZrO2 and Zn1Zr10Oz, using temperature programmed surface reactions of both acetone reactant and possible intermediate compounds including diacetone alcohol, mesityl oxide, phorone, and isophorone. DRIFTS was used to monitor the evolution of surface species while MS was used to track corresponding gas phase products, in an attempt to identify the distinct reaction pathways observed on the two catalysts as well as the role zinc plays in the corresponding reaction pathways. It is found that aldol condensation (or aldolization) of acetone occurs readily at low temperature (298 K), forming mainly acetone dimers (i.e., diacetone alcohol, DAA/mesityl oxide, MSO) on both ZrO2 and Zn1Zr10Oz with the latter being more active. At elevated temperatures, secondary MSO reactions are diverted, mainly caused by the different Lewis basicity on the two catalysts. Over ZrO2, MSO reacts with activated acetone (acetone enolate) to form a surface 4,4-dimethyl-2,6-heptadione (phorone-C), which is further converted into a stable isophorone intermediate. At temperatures above 473 K, polymerization/oligomerization of isophorone along with basic hydroxyl promoted decomposition reactions occur, leading to the formation of heavier carbonaceous surface species and gas-phase side products (methane and CO2). The addition of zinc balances the surface acid-base properties on ZnxZryOz (i.e., Zn1Zr10Oz) via not only enhancing the surface Lewis basicity but passivating the strong acidity. This balance, especially the enhanced surface Lewis basicity largely promotes the α-H abstraction of MSO to form MSO enolate on the Zn1Zr10Oz, which thus favors the aldolization of MSO enolate and acetone, a reaction tends to form 2,6-dimethyl-2,5-heptadien-4-one (phorone-A). Phorone-A then readily decomposes to produce isobutene as a major product at temperature as low as 373 K. Note that, despite the facile formation of isobutene at low temperatures, a high temperature (673 K) is still necessary to release the strongly adsorbed formate/carbonate/acetate species via CO2 formation.

Synthesis of N-benzyl substituted 1,4-imino-l-lyxitols with a basic functional group as selective inhibitors of Golgi α-mannosidase IIb

Inhibition of the biosynthesis of complex N-glycans in the Golgi apparatus is one of alternative ways to suppress growth of tumor tissue. Eight N-benzyl substituted 1,4-imino-l-lyxitols with basic functional groups (amine, amidine, guanidine), hydroxyl and fluoro groups were prepared, optimized their syntheses and tested for their ability to inhibit several α-mannosides from the GH family 38 (GMIIb, LManII and JBMan) as models for human Golgi and lysosomal α-mannoside II. All compounds were found to be selective inhibitors of GMIIb. The most potent structure bearing guanidine group, inhibited GMIIb at the micromolar level (Ki = 19 ± 2 µM) while no significant inhibition (>2 mM) of LManII and JBMan was observed. Based on molecular docking and pKa calculations this structure may form two salt bridges with aspartate dyad of the target enzyme improving its inhibitory potency compared with other N-benzyl substituted derivatives published in this and previous studies.

In Ukrainian

The study of the thermochemical properties of caffeic acid and its surface complexes is important for the pharmaceutical and food industries, medicine and for development of technologies of heterogeneous catalytic pyrolysis of the renewable plant biomass components. In this work, the structure of the surface complexes of caffeic acid on the surface of nanosized cerium dioxide was investigated using FTIR spectroscopy, depending on the degree of the surface coverage (0.1–1.2 mmol/g). Thermal transformations of surface complexes were studied using temperature-programmed desorption mass spectrometry (TPD MS). The analysis of the magnitude of the difference between the assymmetric and symmetric carboxylate stretches СОО - (...) and in case of monodentate coordination, between the C=O and CO stretches (...) was carried out. Based on the obtained values of D, it can be assumed that bidentate chelating complexes ( ≈ 72 cm –1 ), bidentate bridging complexes ( ≈ 110 cm –1 ), and monodentate bound complexes ( ≈ 236 cm –1 ) of caffeic acid are present on the nanoceria surface. In addition, complexes bound through the phenolic hydroxyl groups are present on the surface. This is due to the ability of the nanoceria to generate basic hydroxyl groups that are able to deprotonate the phenolic groups to form phenolates on the surface. The analysis of mass spectrometric data allowed identification of products of thermal transformation and suggested possible ways of forming 3,4-dihydroxyphenylethylene, pyrocatechol, and phenol from surface complexes of caffeic acid, the structure of which was confirmed by data of IR spectroscopy. The kinetic parameters of the phenol formation reaction were calculated. It was established that on the surface of CeO 2 the decarboxylation, dehydration and decarbonylation reactions of caffeic acid occur effectively. These reactions are the desirable processes in biomass conversion technologies.

Direct synthesis of dimethyl carbonate from CO2 and methanol over trifluoroacetic acid modulated UiO-66

Abstract A series of trifluoroacetic acid (TFA) modulated metal-organic frameworks UiO-66 catalysts were synthesized for the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol in this work. Characterization results show that the surface area, pore size, pore volume as well as the amount of missing-linker defects, Lewis acid site, Lewis basic site and hydroxyl of UiO-66-X can be tuned by regulating the amount of TFA modulator. Catalytic activity assessments reveal that TFA modulation enhanced the activity of UiO-66-X. The catalytic activity improvement of the UiO-66-X could be attributed to the increased amount of active sites and the enlargement of porosity originated from TFA modulation. Moreover, a possible reaction mechanism for DMC synthesis from CO2 and methanol over UiO-66-X was proposed based on the in situ FT-IR results.

Redox reaction process between hydrocarbon and adsorbed NOx over lean NOx trap catalyst

In this study, we investigated the redox reaction between a hydrocarbon (HC) and adsorbed NOx over CuPtBa/Al2O3 lean NOx trap (LNT) catalyst. Experimental characterizations included temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), in situ diffuse reflectance Fourier transform spectroscopy (in situ DRIFTs) and Raman spectroscopy. Density functional theory (DFT) calculations were also performed. The model C3H6 first adsorbed to the catalyst surface, and the resulting C3H6-adsorbed species reacted with adsorbed NOx species to form various intermediates such as: carboxylates, enolic compounds, carbonato complexes, Pt-carbonyls, acid anhydrides, basic hydroxyls, nitrogen-containing organic species, acyl chlorides, and ammonium salts. These intermediates participated in subsequent reactions and finally produced the effluent gases CO2, N2, NH3, and H2O. The decomposition ability of adsorbed NOx species indicated that the NOx species participated in the C3H6 oxidation in the order: adsorbed N2O4 > monodentate nitrates > free ionic nitrates > bulk free ionic nitrates. Carbonaceous materials were generated during the C3H6 oxidation process and were consumed as intermediates by gaseous NOx released upon decomposition of the adsorbed NOx species. In summary, the redox reaction between C3H6 and adsorbed NOx followed the Langmuir–Hinshelwood mechanism, and three reaction routes were proposed for the redox process over the studied catalyst. The activation energy barriers determined by DFT + U calculations for the three routes indicated that the initial dissociation of NO3− species in R(2) occurred more easily than the oxidation of C3H6 species in R(1), delivering the active oxygen species that participated in R(1) and R(3). As the reactions proceeded, the higher energy barrier for the complete dissociation of NO2* indicated that the temperature determined the further decomposition of adsorbed NOx species, and R(1) and R(3) were constrained owing to the limited surface active oxygen species from R(2).

Interrelationships among hydrogen permeation, physiochemical properties and early adsorption abilities of titanium.

This study aimed to investigate if the titanium samples with low hydrogen permeation which treated with a novel etching combination: phosphoric acid and sodium fluoride could influence the surface physiochemical properties and early adsorption ability. Titanium samples were treated with three different concentrations of the new formula, as groups A, B and C, and treated with the traditional etching formula, as group T. Zeta potential, contact angle, X-ray photoelectron spectroscopy (XPS) and fibronectin (FN)/vitronectin (VN) adsorption of Sprague-Dawley (SD) rat tibial osteotomies in the initial 30min and MG-63 adsorption in the initial 24 h were detected. Basing on the results of trails and pearson correlation analysis, the low hydrogen permeation into titanium didn't exert an impact on the surface morphology and surface stability. The adsorptions of F, P, S, acid hydroxyl and basic hydroxyl on the surfaces brought no bear on them as well. Surface concave depth and surface skewness showed highly positive correlation and moderate negative correlation with adsorption ability, respectively. Therefore, the surface morphology of titanium treated with the novel etching formula plays the only and primary role on the early adsorption. Because of its specific surface topography, group C showed the best performance which possessed slightly superiority than those of group B and group T, and with the lowest being group A. The low hydrogen permeation into titanium substrate was just benefit for improving the titanium mechanical properties, but not for the surface biochemical traits.

Mechanism of activity enhancement of the Ni based hydrotalcite-derived materials in carbonyl sulfide removal

In this paper, a series of Ni based hydrotalcite-like compounds (HTLCs) were prepared by co-precipitation method. Carbonyl sulfide (COS) removal was investigated over the hydrotalcite-derived oxides (HTO). The properties of desulfurizer and its changes in the desulfurization process were systematically characterized by XRD, SEM, FTIR, CO2-TPD, XPS, XAFS and In-situ DRIFTS. The results showed that the activity series for removal of COS decrease in the following sequence: Ni3Al-HTO > Ni3Fe-HTO > Ni3Cr-HTO. In-situ DRIFTS and quantum chemistry study implied that carbonate and sulfate was formed on the desulfurizer surface. Lewis basic sites and hydroxyl was determined to play a pivotal role for the COS removal. The enhanced activity after trivalent cations substitution is attributed to their high ability to provide electrons as evidenced by results of CO2-TPD, XPS and XAFS. This work is useful to explore feasible routes to improve the performance of desulfurization material for the feed gas purification.

Selective transformation of biomass-derived 5-hydroxymethylfurfural into 2,5-dihydroxymethylfuran via catalytic transfer hydrogenation over magnetic zirconium hydroxides

An economical and effective approach for the selective transformation of biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-dihydroxymethylfuran (DHMF) was developed by catalytic transfer hydrogenation over various magnetic zirconium hydroxides (MZHs). As expected, MZH with a moderate Zr/Fe molar ratio of 2 displayed the highest catalytic activity, resulting in 98.4% HMF conversion and 89.6% DHMF yield at 150 °C for 5 h in the presence of 2-butanol that simultaneously acted as the hydrogen donor and reaction solvent, which was ascribed to its appropriate specific surface area, pore size and acid-base content. Moreover, a plausible reaction mechanism for the catalytic transfer hydrogenation of HMF into DHMF over MHZ(Zr/Fe=2) was also proposed, in which the basic hydroxyl groups with the aid of acidic zirconium metal centers were considered to be responsible for the pivotal hydride transfer via a six-membered ring structure.

Variability of surface components in gold catalysts – The role of hydroxyls and state of gold on activity and selectivity of Au-Nb2O5 and Au-ZnNb2O6 in methanol oxidation

The aim of this study was to use gold catalysts supported on niobium(V) oxide and mixed niobium-zinc oxide in methanol oxidation and to characterize step by step changes in the surface of catalysts that were caused by the activation of the catalyst and methanol oxidation. The purpose was to identify the species important for the activity and selectivity of the reaction. The following surface species were identified by XPS in as prepared catalysts: (i) highly nucleophilic oxygen with the excessive negative charge; (ii) lattice oxygen O2− in the metal oxide; (iii) oxygen in surface hydroxyls; (iv) negatively charged gold NPs (Au0)δ−; and (v) metal cations (niobium, zinc and gold). Activation of catalysts resulted in dehydroxylation accompanied by the formation of highly nucleophilic oxygen and metallic gold showing low activity in selective methanol oxidation. The interaction of the reaction products changed surface species towards basic hydroxyls and next to (Au0)δ− inducing the activity jump and total oxidation of methanol.

Isolated Single-Atomic Ru Catalyst Bound on a Layered Double Hydroxide for Hydrogenation of CO2 to Formic Acid

In order to achieve an economical CO2-mediated hydrogen energy cycle, the development of heterogeneous catalysts for CO2 hydrogenation to formic acid is an urgent and challenging task. In this study, a stable and well-defined single-site Ru catalyst on the surface of a layered double hydroxide (LDH) in a basic medium is proven to be efficient for selective hydrogenation of CO2 to formic acid under mild reaction conditions (2.0 MPa, 100 °C). The electron-donating ability of triads of basic hydroxyl ligands with a particular location is crucial for an active electron-rich Ru center. There is a strong correlation between catalytic activity and adjustable CO2 adsorption capacity in the vicinity of the Ru center. Such electronic metal–support interactions and a CO2 concentration effect result in a significant positive influence on the catalytic activity.

Metal phosphate-supported RuOx catalysts for N2O decomposition

RuOx/M–P–O (M=Mg, Al, Ca, Fe, Co, Zn, La) catalysts were prepared by impregnating commercial metal phosphates with RuCl3, followed by calcination in air at 500°C. The catalytic performance in N2O decomposition was studied. Among these catalysts, RuOx/Ca–P–O (also denoted as RuOx/HAP, HAP=hydroxyapatite) showed the highest activity, achieving complete N2O conversion at 400°C. RuOx/Mg–P–O was the second most active, showing 46.3% N2O conversion at 400°C. The presence of 5.0vol.% O2 or 2.0vol.% H2O in the reaction mixture inhibited the catalytic activity of RuOx/HAP to some extent, but the inhibiting effect was reversible, i.e., the activity was restored after O2 or H2O was retracted. The influences of pretreatment by H2 as well as different Ru-containing precursors on the catalytic performance of RuOx/HAP were also studied. The characterization data indicate that RuOx/HAP has a not-so-small surface area (49.5m2/g), highly dispersed amorphous RuOx species, as well as relatively abundant basic sites, O2-adsorption sites, and surface hydroxyls.

Chemicals from Biomass: Synthesis of Biologically Active Furanochalcones by Claisen–Schmidt Condensation of Biomass-Derived 5-hydroxymethylfurfural (HMF) with Acetophenones

Furanochalcones have been synthesized trough the Claisen–Schmidt condensation of acetophenones and 5-hydroxymethylfurfural (HMF) using different solid base catalysts such as MgO, Al/Mg mixed oxide (HTc) with Lewis basic sites, and a hydrated Al/Mg mixed oxide (HTr) with Bronsted basic sites. The three catalysts provide high selectivity in absence of solvent or in the presence of polar solvents such as ethanol or acetonitrile, however catalysts become rapidly deactivated due to the strong adsorption of HMF and the furanochalcone obtained on the catalyst surface. A further increase in solvent polarity by using a mixture ethanol–water allows obtaining high conversion and high selectivity to furanochalcone using HTc and HTr as catalysts. However, MgO becomes rapidly deactivated which was mainly attributed to structural changes on MgO that is in situ rehydrated into Mg(OH)2 with low activity for aldol condensations. When the reaction was performed using the homogeneous NaOH catalyst, it was found that their activity is higher than that of the solid catalyst, but the selectivity of the later is clearly better. The results indicate that the active phase of the HTc in the ethanol–water medium corresponds to a partially restored hydrotalcite with basic hydroxyl groups. The HTc sample could be applied to the synthesis of a variety of furanochalcones with excellent success, while the catalyst could be reused several reaction cycles without loss of activity.

Identification and binding mechanism of phage displayed peptides with specific affinity to acid⿿alkali treated titanium

Acid⿿alkali treatment is one of means widely used for preparing bioactive titanium surfaces. Peptides with specific affinity to titanium surface modified by acid⿿alkali two⿿steps treatment were obtained via phage display technology. Out of the eight new unique peptides, titanium⿿binding peptide 54 displayed by monoclonal M13 phage at its pIII coat protein (TBP54⿿M13 phage) was proved to have higher binding affinity to the substrate. The binding interaction occurred at the domain from phenylalanine at position 1 to arginine at position 6 in the sequences of TBP54 (FAETHRGFHFSF) mainly via the reaction of these residues with the Ti surface. Together the coordination and electrostatic interactions controlled the specific binding of the phage to the substrate. The binding affinity was dependent on the surface basic hydroxyl group content. In addition, the phage showed a different interaction way with the Ti surface without acid⿿alkali treatment along with an impaired affinity. This study could provide more understanding of the interaction mechanism between the selected peptide and its specific substrate, and develop a promising method for the biofunctionalization of titanium.

Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol–gel methodology

Ce1−xSmxO2(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol–gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5kV, a 7ml/h of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200–1100nm and 50–300nm, before and after calcination at 500°C, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce1−xSmxO2 compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N2) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation–reduction cycles was evaluated using temperature-programmed reduction in a H2 atmosphere (H2-TPR). Acidic–basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH3 and CO2 as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs' potential performance towards NH3 oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO2 adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce0.5Sm0.5O2 NFs compared to bulk powder Ce0.5Sm0.5O2.

Effect of Physicochemical Surface Modifications on Bovine Serum Albumin Adsorption to Tetragonal Zirconia Polycrystal in vitro Through the change of the Zeta Potential.

The technology of physicochemical surface modification is available for enhancing the bioactivity and osseointegration capability of tetragonal zirconia polycrystal (TZP). Hydrophobicity index and electrical charge play important roles in protein adsorption. We previously studied the mechanism underlying the adsorption of bovine serum albumin (BSA) on the surfaces of dental materials and hydroxyapatite in vitro. The aim of the present study was to clarify the correlation among the adsorption of BSA to TZP and physicochemically modified TZP surfaces and the zeta potential of BSA and TZP. We used TZP that was sintered at 1350°C for 2 h in air because this kind of TZP is widely applied in the field of dentistry. Surface physicochemistry was modified with ultraviolet light (UV) and atmospheric-pressure plasma treatment. The zeta potentials were measured with ELSZ-1000 and ELSZ-2000 analyzers (Otsuka Electronics, Hirakata, Japan). All experiments were conducted in 10 mM NaCl (pH 7.0). The zeta potentials of as-received TZP and BSA were negative, but those of UV- and plasma-treated TZP were positive. The reason the zeta potentials of TZP changed positive by physicochemical modification is due to an increase in the amount of basic hydroxyl groups. The zeta potentials of UV- and plasma-treated TZP after BSA adsorption were negative. These results suggested that electrostatic interactions play an important role in BSA adsorption to TZP and modified TZP surfaces, so that this modified surface may control the adsorption of protein.

Low temperature catalytic combustion of 1,2-dichlorobenzene over CeO2–TiO2 mixed oxide catalysts

Ce1−xTixO2 mixed oxide catalysts with various Ti/Ce+Ti ratios were prepared by sol–gel way and used in catalytic combustion of 1,2-dichlorobenzene (o-DCB). Characterization by XRD, Raman, HRTEM, XPS, H2-TPR, O2-TPD, CO2-TPD and NH3-TPD revealed that Ce1−xTixO2 catalysts were identified as the forms of fluorite, monocline and anatase. The incorporation of Ti distorted the crystal structure and thus increased greatly the acidity and the oxygen mobility at high temperature. Ce1−xTixO2 catalysts had considerable activity for o-DCB combustion. TOF obtained on the catalyst with Ti/Ce+Ti ratio of 0.1 at 275°C reached the highest value of 0.64μmol/minm2 (Ti). Ti improved the stability of Ce1−xTixO2 catalysts through retarding the exchange of Cl for basic lattice oxygen and hydroxyl groups. High stability maintained at 330°C for at least 50h. In situ FTIR indicated that o-DCB adsorption was much stronger on Ti species than Ce species and different reaction pathways were related to different types of oxygen species existing on the surface of Ce1−xTixO2 catalysts.

An efficient solid base catalyst from coal combustion fly ash for green synthesis of dibenzylideneacetone

The objective of the investigation was to evaluate the catalytic efficiency of a solid base catalyst (SBC) derived from coal combustion fly ash to synthesize dibenzylideneacetone (DBA, 94% yield). The catalyst was produced using potassium hydroxide (30wt.%) on thermally activated F-type fly ash. The physico-chemical, mineralogical and morphological characterization of the fly ash and catalyst were performed using XRF, FT-IR, BET surface area analyser, XRD and SEM-EDS. The results of such analysis revealed that the catalyst obtained was associated with strong basic hydroxyl (OH) sites that were highly suited to produce DBA by crossed aldol condensation reaction.

Spectroscopic Investigation of Surface-Dependent Acid–Base Property of Ceria Nanoshapes

In addition to their well-known redox character, the acid–base property is another interesting aspect of ceria-based catalysts. Herein, the effect of surface structure on the acid–base property of ceria was studied in detail by utilizing ceria nanocrystals with different morphologies (cubes, octahedra, and rods) that exhibit crystallographically well-defined surface facets. The nature, type, strength, and amount of acid and base sites on these ceria nanoshapes were investigated via in situ IR spectroscopy combined with various probe molecules. Pyridine adsorption shows the presence of Lewis acid sites (Ce cations) on the ceria nanoshapes. These Lewis acid sites are relatively weak and similar in strength among the three nanoshapes according to the probing by both pyridine and acetonitrile. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the ceria nanoshapes, as probed by CO2 adsorption. CO2 and chloroform adsorption indicate that the strength and amount of the Lewis base sites are shape dependent: rods > cubes > octahedra. The weak and strong surface dependence of the acid and base sites, respectively, are a result of interplay between the surface structure dependent coordination unsaturation status of the Ce cations and O anions and the amount of defect sites on the three ceria nanoshapes. Furthermore, it was found that the nature of the acid–base sites of ceria can be impacted by impurities, such as Na and P residues that result from their use as structure-directing reagent in the hydrothermal synthesis of the ceria nanocrystals. This observation calls for precaution in interpreting the catalytic behavior of nanoshaped ceria where trace impurities may be present.