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This paper presents the results of study of titanium–magnesium catalysts often used in polymerization processes, by photoluminescence spectroscopy (PL) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of dibutyl phthalate (DBP) with MgCl2was studied at DBPadded/Mg = 0–1 (mol/mol). The luminescence spectra with excitation at 278 nm and the excitation spectra for main emission bands were recorded. It was shown that DBP adsorbed on magnesium chloride, both in the form of donor–acceptor complexes (D+A–) and in the form of molecular complexes. At DBPadded/Mg +A–complexes occur predominantly; with an increase in DBPadded/Mg, the fraction of molecular complexes increases. Molecular complexes are destroyed during the treatment of the support by TiCl4. In this case, the structure of magnesium chloride is disordered and new coordination–unsaturated sites are formed. This work is a first attempt to apply PL spectroscopy in combination with DRIFTS spectroscopy to study titanium–magnesium Ziegler–Natta catalysts. The application of PL spectroscopy to such systems made it possible to detect interactions within and between donor molecules, which would be particularly challenging to achieve using other spectroscopic methods. Both spectroscopic methods provided crucial information about the existence of two types of complexes on the sample surface which is important for tuning the synthesis procedure of the titanium–magnesium catalysts for olefin polymerization.

Zeolitic imidazolate frameworks (ZIFs) have been extensively examined for their potential in acid–base catalysis. Many studies have demonstrated that ZIFs possess unique structural and physicochemical properties that allow them to demonstrate high activity and yield products with high selectivity. Herein, we highlight the nature of ZIFs in terms of their chemical formulation and the textural, acid–base, and morphological properties that strongly affect their catalytic performance. Our primary focus is the application of spectroscopic methods as instruments for analyzing the nature of active sites because these methods can allow an understanding of unusual catalytic behavior from the perspective of the structure–property–activity relationship. We examine several reactions, such as condensation reactions (the Knoevenagel condensation and Friedländer reactions), the cycloaddition of CO2 to epoxides, the synthesis of propylene glycol methyl ether from propylene oxide and methanol, and the cascade redox condensation of 2-nitroanilines with benzylamines. These examples illustrate the broad range of potentially promising applications of Zn–ZIFs as heterogeneous catalysts.

Solid bifunctional catalysts based on cesium salts of V-containing heteropoly acids (CsHPA: Cs3.5H0.5PW11VO40, Cs4.5H0.5SiW11VO40, Cs3.5H0.5PMo11VO40) and Cs2.5H0.5PMo12O40 were used for studying one-pot hydrolysis–oxidation of potato starch to formic acid at 413–443 K and 2 MPa air mixture. It was shown that the optimum process temperature that prevents formic acid from destruction is 423 K. The studies were focused on the influence of the composition of heteropoly anions on the yield and selectivity of formic acid. Using W–V–P(Si) CsHPA results in the product overoxidation compared to Mo–V-containing CsHPA. The activity of Cs–PMo was significantly lower compared to Cs–PMoV. This may indicate that vanadium plays an important role in the oxidation process. The most promising catalyst was Cs3.5H0.5PMo11VO40 which provided the maximum yield of formic acid equal to 51%. Cs3.5H0.5PMo11VO40 was tested during nine cycles of starch hydrolysis–oxidation to demonstrate its high stability and efficiency.

Catalytic liquid-phase hydrogenation of furfural to commercially important furfuryl alcohol was studied in the presence of Ru-containing catalysts based on Sibunit and zeo-type materials, such as nickel phosphate molecular sieves (VSB-5 and Fe-VSB-5) and zirconium-containing metal–organic frameworks (UiO-66(Zr)-R, R = H and NH2), at 30 and 50°C and 5–25 atm of hydrogen. The yield of furfuryl alcohol was found to depend on the nature of the support and increases in the following order: Ru/UiO-66(Zr)-NH2 < Ru/UiO-66(Zr) < Ru/Fe-VSB-5 < Ru/VSB-5. The effect of hydrogen pressure and temperature on the selectivity toward furfuryl alcohol was investigated.

Bifunctional solid acidic quaternary ammonium salts of Keggin-type vanadium-containing heteropoly acids, such as R3.5H0.5PVMo11O40 (R: (C2H5)4N, (C4H9)4N, (C6H13)4N), and [(C4H9)4N]4.5H0.5SiW11VO40, are capable of one-pot hydrolysis-oxidationconversion (OxFA-processing) of starch to biogenic formic acid. The impact of the reaction conditions and catalyst type was revealed. The highest formic acid yield of 50% was achieved over the best [(C2H5)4N]3.5H0.5PVMo11O40 catalyst, which was active and stable in seven reaction cycles. The kinetic computational model, which described formic acid formation well, was proposed in the presence of the most active [(C2H5)4N]3.5H0.5PVMo11O40 catalyst.

Solid bifunctional catalysts based on cesium salts of V-containing heteropoly acids (CsHPA: Cs

Novel nanoporous composites (MIL/K-SO3H and MIL/Ks-CN) were synthesized by the encapsulation of para-sulfonatocalix[4]arene (K-SO3H) and para-tert-butylthiacalix[4]arene (Ks-CN) with strong ( SO3H) and weak ( CN) acidic functionalities, respectively, in the aluminum(III) 2-aminoterephthalate metal organic framework (NH2-MIL-101(Al)) cavities. MIL/K-SO3H and MIL/Ks-CN materials were prepared by microwave assisted one-step synthesis in situ following to the ship in a bottle approach. According to comprehensive study, textural properties, the morphology and particle sizes of composites depend on the type of the embedded calix[4]arene molecules. Catalytic properties of MIL/K-SO3H and MIL/Ks-CN composites were investigated in the synthesis of physiologically active 1,5-benzodiazepines from 1,2-phenylenediamine and ketones (acetone, acetophenone, methyl ethyl ketone). It was found that their catalytic activity can be adjusted by surface acidity, which depends on the nature of the interactions between functional substituents in the arene “bowl” of calix[4]arenes and NH2 groups in organic linkers of NH2-MIL-101(Al) framework.

Polyethylene m-Y2O3:Eu3+ composites (PECs) containing 0.32, 0.77, and 1.79 wt% of well-dispersed sphere-like m-Y2O3:Eu3+ nanoparticles were obtained by in situ polymerization in the presence of a titanium-magnesium catalyst (TMC). TMC was synthesized by sequential deposition of organic magnesium and TiCl4 on m-Y2O3:Eu3+ that had been previously dehydroxylated at 650 °C. Detailed photoluminescence properties of the obtained composites as a function of m-Y2O3:Eu3+ content were investigated in combination with UV–Vis and IR spectroscopy data. It was shown that Eu3+ ions in monoclinic Y2O3 lattice are responsible for the high red emission of the composites. The effect of the РЕС host on the luminescence properties of m-Y2O3:Eu3+ was revealed. The obtained chromaticity coordinates with improved red color (0.653, 0.347) and high absolute luminescence quantum yield up to 23% make РЕСs potential promising materials for luminescent applications.

Zeolitic imidazolate frameworks MAF-5 and MAF-6 based on Zn2+ and 2-ethylimidazole were demonstrated to be efficient heterogeneous catalysts in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. Activity of MAF-5 was lower in comparison with MAF-6 due to the difference in their structural and textural characteristics. MAF-6 samples with particle size of 190 ± 20, 360 ± 30, and 810 ± 30 nm were prepared at room temperature from [Zn(NH3)4](OH)2 and 2-ethylimidazole. Control of particle size was achieved by variation of type of alcohol in alcohol/cyclohexane media for the preparation of MAF-6. According to this comprehensive study, the yield of PC was found to decrease with increasing crystal size of the MAF-6 material, which was related to the change in textural properties and the number and localization of active sites. The combination of MAF-6 with particle size of with particle size of 190 ± 20 nm and tetrabutylammonium bromide ([n-Bu4N]Br) as co-catalyst led to an approximately 4-fold enhancement in the yield of PC (80.5%). Compared with reported ZIFs catalysts, the efficiencies of MAF-5/[n-Bu4N]Br and MAF-6/[n-Bu4N]Br binary systems were comparable and higher under similar reaction conditions.

Benzodiazepines and their derivatives are a very important class of nitrogen-containing heterocyclic compounds with biological activity that are widely used in medicine. In this study, we demonstrated synthesis of 1,5-benzodiazepines from 1,2-phenylenediamine and ketones (acetone, cyclohexanone, acetophenone, methyl ethyl ketone) in the presence of isostructural porous metal-benzenetricarboxylates of the families MIL-100(M) (M: V3+, Al3+, Fe3+ and Cr3+) and three porous aluminium trimesates Al-BTCs (MIL-96(Al), MIL-100(Al) and MIL-110(Al)). A combination of catalytic, theoretical and physicochemical methods showed that reaction rates and yields of 1,5-benzodiazepines were adjusted by the type of metal ions and accessibility of active sites. The yield of 1,5-benzodiazepines in the presence of MIL-100(M) was comparable with zeolites, such as HY, H-ZSM−5, β-zeolite and heulandite.

Liquid phase catalytic coupling of n-pentanol over VIII group metals (Pt, Pd, Ir, Ru, Rh) on a range of supports (C, Al2O3, TiO2, CeO2, ZrO2) doped with different solid bases was done varying the reaction temperature and gas atmosphere. It was shown that n-pentanol coupling in the selected reaction conditions (180 °C, 10 bar of N2) mainly resulted in the formation of the target product 2-propyl-1-heptanol (Guerbet alcohol), whereas pentanal, 2-propyl-2-heptenal, 2-propyl-1-heptanal, and 2-propyl-1-heptenol were observed in minor quantities. Temperature increase accelerates the reaction and improves selectivity to 2-propyl-1-heptanol. Acid–base properties of the supports also influenced conversion and selectivity correlating with the support base strength TiO2 (860 kJ/mol) < ZrO2 (900 kJ/mol) < C (850–910 kJ/mol) < Al2O3 (935 kJ/mol). For carbon supported catalysts conversion increases in the raw Ir < Ru < Pt < Pd. Analysis of the reaction mechanism for NaOH/Pt/Al2O3 and the relative contributions of vario...

Supported catalysts Al2O3/Cp2ZrX2 and Al2O3(F)/Cp2ZrX2 (X = Me, Cl) for the ethylene polymerization were synthesized by anchoring zirconocene on alumina and alumina, modified with 1–7 wt% fluorine (Al2O3(F)). The study revealed that Al2O3(F)/Cp2ZrMe2 catalysts are active in ethylene polymerization in the absence of organoaluminum cocatalyst, whereas Al2O3(F)/Cp2ZrCl2 catalysts are active in the presence of triisobutylaluminum as a co-catalyst. The metallocene complex was strongly anchored on the support. Active component leaching was not observed during polymerization. The acid–base properties of Al2O3(F) were studied by IR spectroscopy of adsorbed probe molecules: CO, pyridine and CDCl3. A maximum activity of the catalysts was observed in the case of the Al2O3(5%F) support, containing Lewis acid sites with absorption bands (νCO) at 2210–2215 cm−1, Bronsted acid sites with a proton affinity (PA) of 1190 kJ/mol, and weak basic sites with PA 850 and 795 kJ/mol. “Cationic-like” complexes formed on the Lewis acid sites with absorption bands at 2180−2200 cm−1 are inactive at ethylene polymerization.

Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(&mu, Me)2AlMe2+ B(C6F5)4-(SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 &deg, C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-&sigma, polyhexenyl cations arising from SBIZr-Me+ (formed from SBIZr(&mu, Me)2AlMe2+ by release of AlMe3) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-&eta, 3-allyl cations of composition SBIZr-&eta, 3-(1-R-C3H4)+ (R = npropyl), [...]

The synthesis of solketal from acetone and glycerol (I) was investigated in the presence of the isostructural MOFs of the families MIL-100(M) and MIL-53(M) (M = V, Al, Fe and Cr) and mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100 atom/atom). The main products were a five-membered solketal (2,2-dimethyl-1,3-dioxane-4-methanol, (II)) and a six-membered acetal (2,2-dimethyl-dioxane-5-ol, (III)). It was demonstrated that the reaction rate and isomer selectivity depend on different parameters such as the type of metal ion, the length of the M-O bond, the rate constant for the exchange of the water molecules from the first coordination sphere of a metal ion and the value of the zero point of the surface charge (pH PZC ). Investigation of mixed MIL-53(Al,V) shows that the reaction rate and selectivity towards (II) increase with increasing V 3+ content in MIL-53(Al,V). V-containing MOFs possess a high activity and selectivity at 25 °C. The efficiencies of MIL-100(V) and MIL-47(V) were higher than those of H 2 SO 4 , SnCl 2 and p -toluenesulfonic acid at 25 °C. The MIL-100(V) catalyst showed good reusability for 4 catalyst recycles.

The effect of metal ions and functional groups in organic ligands on the photocatalytic properties of metal-carboxylates, such as isostructural MIL-100(M) (M = Al, Fe, V, and Cr), isoreticular UiO-66-R (R = H, NH2, and NO2), MIL-47(V), and MIL-125(Ti), was investigated using the decolorization of methylene blue in aqueous solution at pH 7.0 and 20 °C under UV radiation. The metal-carboxylates were characterized by diffuse reflectance UV/vis measurements. The determination of the band gap (Eg) on the basis of DR-UV/vis measurements showed that Eg values correlate with ionic covalent parameters, i.e., the strength of the interaction between metal and oxygen in the “M+n-O2− pair. According to DR-UV/vis spectroscopic and catalytic investigations, the reactivity of metal-carboxylates correlated with the band-gap value (Eg), which could be adjusted by varying the nature of the metal ions in SBUs or functional groups in the organic ligands.

This article summarizes several approaches for understanding the catalytic chemistry and “structure-surface acidity-reactivity” relationships in a multiplicity of catalytic applications of a continually increasing assemblage of metal-organic frameworks (MOFs) structures. The various spectroscopic techniques for acid-base characterization of MOFs are reviewed. The experimental requirements and the type and nature of probe molecules available are also discussed. Special emphasis is given to the revealing of the surface acid-base effect on the catalytic performance of MOFs.

Natural kaolin and the metakaolin obtained by calcination of kaolin at 650 °C were chemically activated using 0.25–3.0 mol/dm3 HCl solutions. Structural and textural properties of samples were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. The amount of Bronsted acid sites (BAS) was determined by infrared spectroscopy using pyridine as probe molecule. The amount of BAS for kaolin rose with increasing HCl concentration up to 1.0 M, and decreased for higher concentrations, that is related with the leaching of Al from the solid. Effect of HCl concentration on amount of BAS was negligible for metakaolin. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 50 °C. The reaction rate and the selectivity toward octahydro-2H-chromen-4-ol depended on the Bronsted acidity, structural and textural properties of the catalysts. The reaction rate in the presence of kaolin modified by HCl correlated with the amount of BAS. HCl-kaolin samples were more active compared with HCl-metakaolin, while selectivity reaction toward octahydro-2H-chromen-4-ol was larger in the presence of HCl-metakaolin.

In this work we present the data on the formation and composition of new supported catalysts for ethylene polymerization, prepared by interaction of Fe(II) bis(imino)pyridyl complex (LFeCl2) with silica, modified by introduction of alumina compounds (SiO2(nAl)) for generation of Lewis acidic sites (LAS) on the silica surface. Data on the content of LAS with different acidity in SiO2(nAl) supports and on the interaction of LFeCl2 with these sites were obtained. It was found that interaction of LFeCl2 with the most acidic sites of SiO2(nAl) supports leads to formation of the most active catalysts for the ethylene polymerization.

The Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2 H -chromen-4-ol was studied in the presence of natural layered aluminosilicates modified by 0.5 mol/dm 3 HCl, such as montmorillonite, kaolin, and metakaolin obtained by the calcination of kaolin at 650 °C. According to infrared spectroscopy using pyridine as probe molecule, the amount and strength of Bronsted acid sites depend on the type of clay and decrease in the following order HCl-montmorillonite > HCl-kaolin > HCl-metakaolin. The difference in Bronsted acidity and textural properties of clays affected the reaction rate and the selectivity towards octahydro-2 H -chromen-4-ol.

The results of the studies of the acid-base and catalytic properties of metal-organic frameworks (MOFs) are generalized. Significant attention is given to possibilities of spectral methods (IR and ESR) for the study of the nature of acid-base sites and determination of the character of their interaction with organic molecules. The influence has been analyzed of the nature of these sites and structural factors on the catalytic properties of MOFs in reactions of the acid-base type. The presented results demonstrate the possibility of using spectroscopic data for the understanding of the nature and specificity of the catalytic effect of MOFs at the atomic molecular level and for the prediction of their catalytic properties.

The Lewis basicity of typical electron donor compounds used to modify heterogeneous Ziegler–Natta catalysts, such as diakyl ethers, silyl ethers, esters, and ketones, was characterized by determining their effects on the IR frequency of surface silanol groups of silica gel, which correlate with the heat of this specific interaction and with their “donicity”, i.e., with the heat of formation of their complexes with SbCl5. In this manner, ethers and silyl ethers are found to be more basic than ketones and esters. These differences in basicity are likely to affect the stereoregulating properties of such electron donor compounds in Ziegler–Natta polymerization catalysis. By consecutively adsorbing electron donors with various strengths on a MgCl2 support, it was shown that weakly basic donors, such as ethyl benzoate or dibutyl phthalate, are partially displaced by donors with higher basicity, such as valerophenone and propyltrimethoxysilane. This indicates that the displacement of inner donors of the ester ty...

Bei der Suche nach bisher unerkannten Ruhezustanden von Zirconocenkatalysatoren fur die Olefinpolymerisation ergaben kombinierte UV/Vis- und NMR-spektrometrische Methoden, dass kationische, kettentragende Zr-Allyl-Komplexe etwa 90 % der Katalysatorkonzentration ausmachen. Andere am Katalyseprozess beteiligte Katalysatorspezies mussen daher aus dem Allylreservoir regeneriert werden, in das sie offenbar haufig zuruckfallen.

Effect of basicity of porous metal-carboxylates, such as MIL-100(Al), Cu3(BTC)2·(H2O)3, UiO-66 and amino-modified UiO-66 materials (UiO-66-NH2) on their catalytic performance, was studied in the Knoevenagel condensation of benzaldehyde with malononitrile to 2-benzylidenemalononitrile. According to physicochemical studies, the strength of the basic sites for MIL-100(Al), Cu3(BTC)2·(H2O)3, UiO-66 was in the range of 830–839 kJ/mol, while the amount of basic sites decreased in the order MIL-100(Al) > Cu3(BTC)2·(H2O)3 > UiO-66. The insertion of NH2 groups into the UiO-66 framework led to an increase in the strength of basic sites from 839 to 867 kJ/mol. The catalytic activity of metal carboxylates correlated with the amount of basic sites and the strength of the interaction between metal and oxygen in the “M+n–O2− Lewis acid–base” pair, which was estimated from ionic covalent parameters. The activity of the UiO-66-NH2 materials was higher than that of UiO-66.

Adsorption of valeric acid and 5-nonanone on zirconia was investigated by DRIFTS and UV–vis DRS methods. Physical adsorbed and chemisorbed acid and ketone species have been found. Based on the experimental data obtained in this work and on DFT calculations reported in the literature two β-ketoacid routes depending on surface carboxylate intermediates were proposed: (i) via interactions of surface monomolecular monodentate valerate with either monomolecular bridging bidentate or chelating bidentate and (ii) via interactions of two monodentates coordinated to the same Zr cation. The relative contribution of each of them in the overall ketone formation over metal oxide surfaces depends on the reaction conditions.

The catalytic performance of porous metal–benzenetricarboxylates, such as MIL-100(Al, Fe and Cr), MIL-110(Al) and MIL-96(Al), was investigated with a combination of physicochemical and catalytic approaches in the rearrangement of α-pinene oxide to campholenic aldehyde (CA). The investigation of Lewis acidity was done by EPR and IR spectroscopy using 2,2′,6,6′-tetramethyl-1-piperidinyoxyl radical and benzonitrile as the probe molecules, respectively. For Al–BTCs, both these methods showed a decrease in the amount of Lewis acid sites as follows: MIL-100 > MIL-110 > MIL-96. The reaction rate and selectivity toward CA also decreased in the same order. A relatively good correlation between selectivity toward CA and the electronegativity of the metal ion was found for isostructural MIL-100(Al, Fe and Cr). The selectivity toward CA decreased in the order: MIL-100(Al) > MIL-100(Fe) > MIL-100(Cr). The high selectivity toward CA in the presence of MIL-100 has been suggested to originate from the unique structure of this material, which favors shape selectivity.

A family of isoreticular metal-organic frameworks (MOFs), based on the UiO-66 structure, were synthesized from the two linker ligands containing electron-donating NH 2 -groups (2-amino-benzenedicarboxylic acid (H 2 N-H 2 BDC)) and electron-withdrawing NO 2 -groups (2-nitro-benzenedicarboxylic acid (O 2 N-H 2 BDC)). The catalytic performance of these materials was investigated with a combination of physicochemical and catalytic approaches in acetalization of benzaldehyde with methanol. The investigation of basicity and Lewis acidity was done by IR spectroscopy using CDCl 3 and 5-nonanone as probe molecules, respectively. The combination of physicochemical and catalytic investigations demonstrates that acid–base and catalytic properties of these materials depend on amount and type of functional groups presented in the linker units. Insertion of electron-donating NH 2 -groups into linker ligand leads to increase in the strength of basic sites in contrast to electron-withdrawing NO 2 -groups. The strength of Lewis acid sites decreases in order of UiO-66-NO 2 > UiO-66 > UiO-66-NH 2 , that leads to the decrease in their catalytic activity in acetalization of benzaldehyde with methanol in the same order.

Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. The chloro-bridged heterodinuclear ansa-zirconocenium cation [(SBI)Zr(μ-Cl)_2AlMe_2]^+ (SBI = rac-dimethylsilylbis(1-indenyl)), present in toluene solution as its B(C_6F_5)_4^– salt, thus gives rise to an EPR signal assignable to the complex (SBI)Zr^(III)(μ-Cl)_2AlMe_2, while (SBI)ZrIII-Me and (SBI)Zr^(III)(μ-H)_2Al^(i)Bu_2 are formed by reduction of [(SBI)Zr(μ-Me)_2AlMe_2]^+ B(C_6F_5)_4– and [(SBI)Zr(μ-H)_3(AliBu_2)_2]^+ B(C_6F_5)_4^–, respectively. These products can also be accessed, along with (SBI)ZrIII-iBu and [(SBI)ZrIII]^+ AlR_4^–, when (SBI)ZrMe_2 is allowed to react with HAl^(i)Bu_2, eliminating isobutane en route to the Zr(III) complex. Further studies concern interconversion reactions between these and other (SBI)Zr(III) complexes and reaction mechanisms involved in their formation.

This review is devoted to the discoveries and knowledge developed in the past 10–15 years in the area of the design and applications of nickel phosphate molecular sieves (VSB-1 and VSB-5). The main textural and physicochemical characteristics of these materials that make them suitable for catalysis were viewed at the molecular and atomic levels. According to various spectroscopic investigations, the type of metal ions introduced into the VSB-1 and VSB-5 framework allows one to adjust the nature of the surface functional groups and thereby, affects the catalytic properties. Emphasis is placed upon the relationship between the physicochemical properties and their catalytic properties in hydrogenation, oxidation and acid–base type reactions. Because of the simultaneous existence of acid–base and red-ox pairs, nickel phosphate molecular sieves, similar to a chameleon, can adapt to catalytic systems and provide necessary active sites. This review clearly demonstrates that nickel phosphate molecular sieves (VSB-n series) possess promising catalytic properties: e.g., shape selectivity, red-ox and acid–base catalysis, and we expect that this work opens the door to novel applications of these materials in catalysis.

The effect of acid modification of a natural montmorillonite clay (MM) by HNO3 on the catalytic properties of MM from Dash-Salakhlinsk (Kazakhstan) has been investigated in the synthesis of solketal from glycerol and acetone in solvent free and acetonitrile media. HNO3 concentration allowed to control the chemical composition, the surface acidity, the porous structure of the acid-activated MMs and their catalytic performance. The main reaction product was solketal with 86.6–98% selectivity. Conversion of glycerol depended on the Bronsted acidity. The most active sample, namely, MM activated with 0.5 mol/dm3 HNO3, showed good reusability for 3 catalyst cycles.

The aim of this study was to investigate the correlation between the basic and catalytic properties of brucite and Mg,Al-layered double hydroxides (Mg,Al-LDHs) in the reaction of propylene oxide with methanol. The basic properties of the solids were investigated by FT-IR spectroscopy using CDCl3 as probe molecule and Hammett acidity titration with n-butylamine and benzoic acid. Both the increase in the activation temperature and the decrease in Al content favored the increase in the basicity of Mg,Al-LDH. The nature of “Mn+ O2− Lewis acid-base” pairs was a key factor to control the catalytic behavior of the solids. The length of the M-O bond, the basicity of the oxygen ion and the strength of the metal ion on the surface affected the catalytic activity of the solids and their isomer selectivity in the reaction between methanol and propylene oxide to form 1-methoxy-2-propanol. It was demonstrated that brucite(150) can be applied as catalyst for at least four successive cycles without loss of activity.

This article summarizes several approaches for understanding the catalytic chemistry and “structure-surface acidity-reactivity” relationships in a multiplicity of catalytic applications of a continually increasing assemblage of metal-organic frameworks (MOFs) structures. The various spectroscopic techniques for acid-base characterization of MOFs are reviewed. The experimental requirements and the type and nature of probe molecules available are also discussed. Special emphasis is given to the revealing of the surface acid-base effect on the catalytic performance of MOFs.

The aminated silica gels SiO2/SOCl2/NH3 (I), SiO2/SiCl4/NH3 (II), SiO2/BCl3/NH3 (III), and SiO2/γ-aminopropyltriethoxysilane (SiO2/APTES, IV) have been synthesized. According to DRIFT spectroscopy and chemical analysis data, the surface amino groups of I–III are “free,” while those of IV interact with the surface OH groups of the silica gel and with one another. The strength of basic sites has been measured on the proton affinity (PA) scale as the shift of the ν(CD) band of adsorbed deuterochloroform. The basicity of an aminated silica gel depends on its chemical composition. Silica gel IV (PA = 938 kJ/mol) is a stronger base than I–III (PA = 829 kJ/mol). As the basicity of the NH2 group decreases, the N-H stretching band shifts to higher frequencies.

Reactive species in SiO 2 -supported, zirconocene-based olefin-polymerization catalysts have been characterized by comparison of their UV-vis spectra with those of related, NMR-spectroscopically identified catalyst species in homogeneous solution. Neutral zirconocene dihydride complexes are found to arise in hydrocarbon solutions as well as on SiO 2 supports when catalyst systems that contain rac-Me 2 si(ind) 2 ZrCl 2 and methylaluminoxane (MAO) are modified by addition of diisobutylaluminum hydride or triisobutylaluminum. These complexes, tentatively formulated as adducts with Lewis-acidic alkylaluminum species AlR 2 X, rac-Me 2 Si(ind) 2 ZrH 2 ·{nAlR 2 X}, are reconverted into the initial reactive zirconocene cations upon addition of isobutene to these reaction systems.

Formation of the CrO 3 /SiO 2 catalyst prepared by the reaction of CrO 3 vapor with silica pre-dehydroxylated at 250–800 °C was studied by the DRIFT and DRS methods. It was found that CrO 3 reacts with the silica OH-groups at 250 °C to produce various chromate species and water. The latter is removed from the catalyst surface by vacuumation at 250 °C. It was found the nature of CrO 3 interaction with silica and the structure and composition of the surface species depend on silica dehydroxylation temperature. The reactions of CrO 3 with the silica dehydroxylated at 250, 400 and 800 °C yielded, respectively, monochromates; mono- and dichromates; polychromates. The catalyst activity at ethylene polymerization strongly increases with increasing dehydroxylation temperature, especially in the range of 250–400 °C. The results obtained prove di- and polychromates to be the active components of the Phillips type chromium-oxide catalysts from which the active centers are formed at interaction of the active component with co-catalyst (AlEt 3 ) and ethylene. Active centers contain the surface organo-chromium compounds with chromium ions in low oxidation states (lower than Cr(VI)).

IR spectroscopy has been used to study the interaction of silica with PhNEt 2 (N) and B(C 6 F 5 ) 3 (B) and subsequent interaction of the support SiO 2 /[N + B] with dimethylzirconocene Me 2 Si(2-Me-Ind) 2 ZrMe 2 (“Zr”). The data were obtained on the composition of the surface compounds appeared at both stages of catalyst synthesis. It has been shown that (B) and (N) interact with OH groups of silica to form ionic pair [H NR 3 ] + [(C 6 F 5 ) 3 B O Si ] − (IP-1). Cation fragment of this pair contains highly reactive N H bond with a.b. at 3230 cm −1 . It has been found that N H groups in a part of IP-1 complexes react with neighboring OH groups of silica by hydrogen bonding that gives complexes IP-2. It has been shown that “Zr” complexes interact both with complexes IP-1 and IP-2. As “Zr” reacts with IP-1, zirconium ionic complexes IP-3 containing Zr Me bond are formed on silica. These complexes are suggested to be the precursor of the polymerization active sites. The reaction of “Zr” with IP-2, most likely, produces surface zirconium compound containing no Zr Me bonds and inactive for propylene polymerization.

Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N 2 -adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Bronsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2 H -chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Bronsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2 H -chromen-4-ol.

UV-vis spectroscopic data indicate that zirconocene cations with Zr-bound allylic chain ends are generally formed during olefin polymerization with zirconocene catalysts. The rates and extent of their formation and of their re-conversion to the initial pre-catalyst cations depend on the types of zirconocene complexes and activators used.

In a search for the hitherto elusive catalyst resting state(s) of zirconocene-based olefin polymerization catalysts, a combination of UV/Vis and NMR spectrometric methods reveals that polymer-carrying cationic Zr allyl complexes make up about 90 % of the total catalyst concentration. Other catalyst species that take part in the polymerization process have to be generated from this allyl pool into which they appear to relapse rather frequently.

The structure of solid methylalumoxane (MAO) and its behavior in the temperature interval from 20 to 250°C have been studied using IR spectroscopy in diffusion reflection mode (DRIFT) and mass-spectrometric (MS) methods. It has been shown that three-dimensional MAO molecule may entrap water molecule in its volume (absorption bands (a.b.) 3550 cm−1 in the IR-spectrum). Using a density functional theory (DFT) quantum-chemical method, the three-dimensional molecular model of MAO with composition (Al(CH3)O)12, comprising water molecule in its structure, has been calculated. The release of the water molecule from the structure of MAO molecule is accompanied by the protolysis of AlCH3 bonds and methane evolving. This reaction seems to be responsible for the observed evolving of methane on the MAO aging. As the temperature of MAO heating increases from 20 to 150°C, the process of methane evolving intensifies. The heating of the solid MAO samples is also accompanied by the release of trimethylaluminum (TMA) in significant amount (0.18 mole AlMe3/mole AlMAO at 100°C). Obviously, the released TMA was strongly associated with the MAO in the initial sample. The data on the activity in the ethylene polymerization of catalyst Cp2ZrCl2/MAO prepared with the use of the MAO samples dried at temperatures 20–250°C are presented as well.

1 H and 2 H NMR spectroscopic monitoring of ferrous species formed via interaction of 2,6-bis[1-2,6-dimethylphenylimino)ethyl]pyridineiron (II) chloride (1) with AlMe 3 , MAO, AlMe 3 /B(C 6 F 5 ) 3 and AlMe 3 /CPh 3 (C 6 F 5 ) 4 is reported. At interaction of 1 with MAO in toluene solution, the new stable heterodinuclear neutral complexes with proposed structures LFe(II)(Cl)(u-Me) 2 AlMe 2 and LFe(II)(Me)(u-Me) 2 AlMe 2 are formed (L is initial tridentate ligand). Complex LFe(II)(Cl)(u-Me) 2 AlMe 2 predominates at low Al/Fe ratios (less than 50), while LFe(II)(Me)(U-Me) 2 AlMe 2 at high Al/Fe ratios (more than 500). Complex assigned to LFe(II)(Me)(u-Me) 2 AlMe 2 can be prepared via interaction of 1 with AlMe 3 . Activation of LFe(II)(Me)(u-Me) 2 AlMe 2 by B(C 6 F 5 ) 3 and CPh 3 B(C 6 F 5 ) 4 gives rise to formation of new complexes with proposed structures [LFe(u-Me) 2 AlMe 2 ] + [MeB(C 6 F 5 ) 3 ] - and [LFe(u-Me) 2 AlMe 2 ] + [B(C 6 F 5 ) 4 ] - . Unexpectedly, the activity at ethylene polymerization was even higher for 1/AlMe 3 than for 1/MAO catalytic system. The co-catalytic activity of MAO towards 1 dramatically decreased with the diminishing of AlMe 3 content in the composition of MAO. Activity of the catalyst 1/AlMe 3 and the molecular structure of polyethylene produced do not change noticeably at the addition of B(C 6 F 5 ) 3 to 1/AlMe 3 . These data allow to suggest, that active species of 1/AlMe 3 and 1/MAO systems are neutral methylated ferrous complexes but not cationic intermediates. Probably, complex LFe(II)(Me) 2 AlMe 2 is the closest precursor of these active species.

Lewis acidic sites (LAS) of silica, modified with TMA and MAO samples differed by TMA content, have been characterized by IR spectroscopy (CO adsorption as probe molecule at 77 K). Two types of LAS were found on the surface of silica modified with MAO and TMA: M LAS of moderate strength (νCO= 2204−2212 cm−1) and weak W LAS (νCO= 2194 cm−1). The concentration of these acidic sites has been estimated. It was shown by IRS study Cp2ZrMe2 interacts both with W LAS and M LAS. Correlation between the amount of M LAS and the activity of ethylene polymerization has been found.

IR spectroscopy has been used to study the interaction of silica with two methylaluminoxane (MAO) samples differed by trimethylaluminium (TMA) content and with TMA. MAO and TMA have been shown to react with silica in a different way. Whereas TMA interacts with terminal hydroxyl groups of silica via the protolysis reaction, MAO mainly adsorbs on the surface hydroxyl groups of silica without noticeable protolytical reaction with them. When silica is treated with commercial grade MAO with significant TMA content, the silica surface hydroxyl groups mainly interacts with TMA and MAO adsorbs on the surface of SiO 2 /TMA sample. Lewis acidic sites (LAS) of silica, modified with TMA and MAO samples differed by TMA content, have been investigated by IR spectroscopy (CO adsorption as probe molecule at 77 K). Two types of LAS were found on the surface of silica modified with MAO and TMA: LAS of moderate strength ( ν CO =2204–2212 cm −1 ) and weak LAS ( ν CO =2194 cm −1 ). The concentration of these acidic sites was estimated. By anchoring of Cp 2 ZrCl 2 on silica, modified with TMA and MAO, the corresponding catalysts SiO 2 /TMA/Cp 2 ZrCl 2 and SiO 2 /MAO/Cp 2 ZrCl 2 were prepared and tested at ethylene polymerization. Some correlations between the amount and strength of surface LAS of supports, catalysts composition and their activity are discussed. It is proposed that the surface active species are formed at zirconocene interaction with the most strong LAS.