Ivan V. Kozhevnikov

Heteropoly Acids and Related Compounds as Catalysts for Fine Chemical Synthesis

Abstract Catalysis by heteropoly acids (HPAs) and related compounds is a field of growing importance, attracting increasing attention worldwide, in which many new and exciting developments are taking place in both research and technology [1–111, HPAs are polyoxometalates incorporating anions (heteropolyanions) having metal-oxygen octahedra as the basic structural units [ll-141. Among a wide variety of HPAs those belonging to the so-called Keggin series are the most importance for catalysis. They include heteropolyanions (HPANs)

New acid catalyst comprising heteropoly acid on a mesoporous molecular sieve MCM-41

New solid acid catalysts, consisting of heteropoly acid (HPA) H3PW12O40 (PW) supported on a mesoporous pure-silica molecular sieve MCM-41, have been prepared and characterized by nitrogen physisorption, X-ray diffraction, FT-IR, and31P magic angle spinning NMR. The PW/MCM-41 compositions with PW loadings from 10 to 50 wt% have ∼ 30 Å uniformly-sized mesopores. HPA retains the Keggin structure on the MCM-41 surface and forms finely dispersed HPA species. No HPA crystal phase is developed even at HPA loadings as high as 50 wt%. PW/MCM-41 exhibits higher catalytic activity than H2SO4 or bulk PW in liquid-phase alkylation of 4-t-butylphenol (TBP) by isobutene and styrene. In the alkylation of TBP by styrene, PW/MCM-41 shows a size selectivity compared to bulk PW and PW/SiO2, providing higher yields of a 2-(1-phenylethyl)-4-t-butylphenol, at the expense of the more bulky 2,6-bis-(1-phenylethyl)-4-t-butylphenol. The PW/MCM-41 compositions, having strong acid sites and a regular mesoporous system, are promising catalysts for the acid-type conversion and formation of organic compounds of large molecular size.

Study of catalysts comprising heteropoly acid H3PW12O40 supported on MCM-41 molecular sieve and amorphous silica

With the aim of obtaining pure Keggin-type heteropoly acid (HPA) species on siliceous surfaces, the preparation of HPA catalysts, comprising of 10 to 50 wt.% H3PW12O40 (PW) supported on an amorphous silica or a mesoporous all-silica molecular sieve MCM-41, was studied. The state of HPA on the siliceous surface was characterized by 31P NMR, XRD and TEM. Impregnating MCM-41 or amorphous SiO2 with an aqueous solution of PW gave catalysts with, in general, two HPA species: one with intact Keggin structure (A) and the other with a different structure (B), supposedly, H6P2W18O62 (P2W18) and/or H6P2W21O71 (P2W21). The relative amount of species A and B depends on HPA loading, with A dominating. At higher loadings, 30–50 wt.%, A is practically the only one present on the surface; at lower loadings, both species exist, the amount of B increasing as the HPA loading decreases. In contrast, catalysts prepared by impregnation with a methanol solution of HPA contained exclusively Keggin-type A over the whole range of PW loading. In the PWMCM-41 catalysts, as shown by TEM, the PW species are mainly located inside the MCM-41 pores. The B species was about 8 times as active as A in the liquid-phase trans-de-t-butylation of 2,6-di-t-butyl-4-methylphenol.

Friedel–Crafts acylation and related reactions catalysed by heteropoly acids

Abstract Recent studies on catalysis by heteropoly acids (HPA) for the Friedel–Crafts acylation of arenes and related Fries rearrangement of aryl esters are reviewed. It is demonstrated that HPA-based solid acids are efficient and environmentally friendly catalysts for these reactions, usually superior in activity to the conventional acid catalysts such as H2SO4 or zeolites.

17O NMR determination of proton sites in solid heteropoly acid H3PW12O40.31P,29Si and17O NMR, FT-IR and XRD study of H3PW12O40 and H4SiW12O40 supported on carbon

Abstract17O MAS NMR spectra for solid heteropoly acid (HPA) H3PW12O40 are reported. Comparison of solid-state and solution17O resonances shows that in the solid dehydrated H3PW12O40 terminal W=O oxygen atoms are the predominant protonation sites. H3PW12O40 and H4SiW12O40 supported on chemically activated carbon have been studied by means of NMR, FT-IR and XRD. The carbon-supported HPAs retain their Keggin structure and form finely dispersed HPA species. No HPA crystal phase is developed even at an HPA loading as high as 45 wt%.31P,29Si and17O MAS NMR spectra for bulk and carbon-supported HPAs indicate interaction of the HPA Keggin units with the carbon surface, causing large line broadening in the NMR spectra.

Highly efficient liquid-phase oxidation of primary alcohols to aldehydes with oxygen catalysed by Ru–Co oxide

RuIV-CoIII (1:1.5) binary oxide, prepared by co-precipitation, is a highly efficient solid catalyst for the oxidation of primary alcohols to aldehydes with O2 (76-95% selectivity at 54-100% conversion) in a liquid phase under atmospheric pressure.

Hydration and acetoxylation of monoterpenes catalyzed by heteropoly acid

The liquid-phase hydration and acetoxylation of limonene (1), β-pinene (2) and α-pinene (3) catalyzed by dissolved or silica-supported heteropoly acid H3PW12O40 (PW) in acetic acid and acetic acid/water solutions have been studied. All three substrates give α-terpineol (4) as the main product along with α-terpenyl acetate (5). The reaction rate increases in the order: limonene<α-pinene<β-pinene. Synthetically useful homogeneous and heterogeneous acetoxylation and hydration of 1, 2 and 3 into 4 and 5 have been developed. At room temperature under optimized conditions, 2 and 3 form a mixture of 4 and 5 with 85% selectivity at 90% substrate conversion. 1 gives 4 and 5 with 85% selectivity at 50% conversion, with the main product being ester 5 in acetic acid (4/5≈30/70) and alcohol 4 in HOAc/H2O (90/10 v/v) solutions (4/5≈85/15). Virtually no oligomerization of monoterpenes occurs under the optimized conditions. The catalyst can be separated without neutralization and may be reused. The PW shows a much higher catalytic activity than conventional acid catalysts such as H2SO4 and Amberlyst-15.

Liquid-phase oxidation of alcohols with oxygen catalysed by modified palladium(II) oxide

Benzyl and trans-cinnamyl alcohols are heterogeneously oxidised to the corresponding aldehydes by O2 in liquid phase at 100 °C and ambient pressure using hydrous binary PdII–M oxides (M=CoIII, FeIII, MnIII and CuII) as catalysts. Modification of PdII oxide with transition metal cations greatly improves the catalytic activity and selectivity to aldehydes, CoIII and FeIII being the most effective promoters. In benzyl alcohol oxidation in toluene solution, the Pd–Co system gives 85–100% selectivity to aldehydes at 53–95% alcohol conversion in 15–60 min reaction time. The catalyst can be re-used without loss of its activity and selectivity. The presence of a certain amount of water in the catalysts is essential for their performance. From TGA, the composition of the optimal Pd–Co catalyst can be approximated as PdO·(0.13–1.0)CoO(OH)·(2–3)H2O. The oxidation of alcohols on Pd–M oxide catalysts is accompanied by transfer hydrogenation and decarbonylation side reactions, which is similar to the oxidation on the palladium metal. This indicates that the oxidation of alcohols on Pd–M oxide catalysts occurs via a dehydrogenation mechanism, with hydrogen being present on the catalyst surface.

Proton sites in Keggin heteropoly acids from17O NMR

The structure of the bulk proton sites in dehydrated solid Keggin-type heteropoly acids (HPA) H3PW12O40 and H4SiW12O40 was determined by17O NMR. The terminal W=O oxygen atoms in Keggin heteropolyanions were found to be the predominant protonation sites. The protonation of HP As in solution is also discussed on the basis of17O NMR data.

Epoxidation of oleic acid catalyzed by peroxo phosphotungstate in a two-phase system

Abstract The peroxo phosphotungstate {PO 4 [WO(O 2 ) 2 ] 4 } 3− is a highly efficient catalyst (or catalyst precursor) for the phase-transfer epoxidation of oleic acid by aqueous 35–60% hydrogen peroxide, yielding 84% epoxide (based on oleic acid) at 95% oleic acid conversion and 800–1200 catalyst turnovers, without using a chlorocarbon solvent.