Cs-5[alpha-SiW11O39RuIII(H2O)]8H(2)O heteropolysalt with a Keggin structure was successfully synthesized, and its physicochemical characteristics were determined via X-ray diffraction, UV-Vis spectroscopy, Fourier-transform infrared and Brunauer, Emmett and Teller surface area measurements. The acid-base properties were evaluated via isopropanol decomposition. The catalytic performance for the CO(2 )methanation reaction was evaluated in a fixed-bed reactor at atmospheric pressure by varying the process parameters, which included the reaction temperature (200-450 degrees C), reactant mole ratio H-2/CO2 (1, 2 and 4) and flow rate (1, 1.5 and 2 L/h). The experimental results showed that Cs-5[alpha-SiW11O39RuIII(H2O)]8H(2)O exhibited the best compromise between con-version and selectivity at 350 degrees C, with a H-2/CO(2 )mole ratio of 4 and a flow rate of 1 L/h.

The catalytic activity of various Keggin polyoxometalate catalysts has been investigated in the gas-phase partial oxidation of toluene to produce benzyl alcohol and benzaldehyde. The catalyst systems HPMo12O40, HPMo11VO40, FePMo12O40, and PMo11FeO39 were prepared and characterized by FT-IR, UV-visible, SEM, XRD, TGA, and cyclic voltammetry. The acid/base properties were evaluated using the decomposition of isopropanol. Catalytic studies were carried under atmospheric pressure and over the temperature range 200°C–350°C, using carbon dioxide as a mild oxidant. Toluene conversion and product distribution depend mainly on the catalyst composition and operating conditions. In addition to benzaldehyde, benzyl alcohol is obtained with a high selectivity on the PMo11FeO39 catalyst. The kinetic data show that the reoxidation of the reduced catalyst is the rate-limiting step for the partial oxidation reaction of toluene.

Heteropolyacids of Keggin structure, \(\hbox {H}_{3}\hbox {PMo}_{12}\hbox {O}_{40}\), \(\hbox {H}_{3}\hbox {PMo}_{11}\hbox {WO}_{40}\) and the salts \(\hbox {K}_{3}\hbox {PMo}_{11}\hbox {WO}_{40}\) and \(\hbox {K}_{2.5}\hbox {Fe}_{0.08}\hbox {H}_{0.26}\hbox {PMo}_{11}\hbox {WO}_{40}\) were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared (FTIR), low-temperature nitrogen adsorption and \(^{31}\)P MAS NMR spectroscopy. The acid-base properties were evaluated using the isopropanol decomposition. They were tested in oxidative dehydrogenation (ODH) of ethylbenzene in the temperature range 300–400 \(^{\circ }\hbox {C}\) at atmospheric pressure with the mild oxidants carbon dioxide and nitrous oxide, the major actors in the greenhouse effect. The results show that the best compromise between conversion and selectivity is obtained for the mixed K/Fe salt of \(\hbox {PMo}_{11}\hbox {WO}_{40}\) at a relatively low temperature, namely \(350^{\circ }\hbox {C}\).

Heteropolyacids of Keggin structure, H3PMo12O40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {H}_{3}\hbox {PMo}_{12}\hbox {O}_{40}$$\end{document}, H3PMo11WO40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {H}_{3}\hbox {PMo}_{11}\hbox {WO}_{40}$$\end{document} and the salts K3PMo11WO40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {K}_{3}\hbox {PMo}_{11}\hbox {WO}_{40}$$\end{document} and K2.5Fe0.08H0.26PMo11WO40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {K}_{2.5}\hbox {Fe}_{0.08}\hbox {H}_{0.26}\hbox {PMo}_{11}\hbox {WO}_{40}$$\end{document} were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared (FTIR), low-temperature nitrogen adsorption and 31\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{31}$$\end{document}P MAS NMR spectroscopy. The acid-base properties were evaluated using the isopropanol decomposition. They were tested in oxidative dehydrogenation (ODH) of ethylbenzene in the temperature range 300–400 ∘C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{\circ }\hbox {C}$$\end{document} at atmospheric pressure with the mild oxidants carbon dioxide and nitrous oxide, the major actors in the greenhouse effect. The results show that the best compromise between conversion and selectivity is obtained for the mixed K/Fe salt of PMo11WO40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {PMo}_{11}\hbox {WO}_{40}$$\end{document} at a relatively low temperature, namely 350∘C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$350^{\circ }\hbox {C}$$\end{document}. Synopsis:Heteropolycompounds of Keggin structure catalysed oxidative dehydrogenation of ethylbenzene with high selectivity to styrene. It was noted that acidic properties of the catalytic system, reaction conditions and catalyst composition affect the oxidative dehydrogenation reaction.

Heteropolyacids of Keggin structure, H_3PMo_12O_40 , H_3PMo_11WO_40 and the salts K_3PMo_11WO_40 and K_2.5Fe_0.08H_0.26PMo_11WO_40 were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared (FTIR), low-temperature nitrogen adsorption and ^31 P MAS NMR spectroscopy. The acid-base properties were evaluated using the isopropanol decomposition. They were tested in oxidative dehydrogenation (ODH) of ethylbenzene in the temperature range 300–400 ^∘C at atmospheric pressure with the mild oxidants carbon dioxide and nitrous oxide, the major actors in the greenhouse effect. The results show that the best compromise between conversion and selectivity is obtained for the mixed K/Fe salt of PMo_11WO_40 at a relatively low temperature, namely 350^∘C . Graphical Abstract Synopsis: Heteropolycompounds of Keggin structure catalysed oxidative dehydrogenation of ethylbenzene with high selectivity to styrene. It was noted that acidic properties of the catalytic system, reaction conditions and catalyst composition affect the oxidative dehydrogenation reaction.

Partial oxidation of methane by molecular oxygen and nitrous oxide was studied in the presence of catalytic amounts of the Keggin-type heteropolyoxometalates of general formula [PW11MO39](7−n)− with M=Co(II), Ni(II), and Fe(III). The catalysts were prepared by refilling the vacant site of the lacunary precursor K7PW11O39 by the metal additives and characterized by 31P NMR, UV–vis and IR spectra, XRD, TGA/DTA and cyclic voltammetry. The oxidation reaction was performed at atmospheric pressure at 873 or 923K. Reaction products observed were methanol, formaldehyde, carbon oxides and water. Most prominent results are the following: (i) selectivity to oxygenates as high as 48% (conversion 5%) was obtained; (ii) cobalt and iron doped polyoxometalates were the most active and selective catalysts; (iii) N2O was more reactive and selective than O2. The activity rise was correlated with the increase of the oxidant character of the cluster metal. Kinetic study and catalyst behaviour suggested that reaction paths were different for nitrous oxide and molecular oxygen. For N2O, methane would be oxidized by MO2 centres to methoxy species, precursors of both methanol and formaldehyde. For O2, methane activation rather involves hydrogen abstraction by the lattice oxygen on M=O centres to form metal-methyl species, the key-intermediates in the oxidation processes.

The activation of C–H bonds of hydrocarbon over different heteropolycompounds (HPC) HPMo12O40, FePMo12O40 and PMo11FeO39 catalysts was studied. The catalysts were prepared and characterized by several physical techniques (BET, XRD, FTIR, Raman and 31P MAS NMR) and the catalytic properties evaluated in the temperature range of 250–400°C. This study examined the relation between the acid–base, redox properties of heteropolycompounds and the reaction behavior of various hydrocarbons n-hexane, cyclohexane, cyclohexene and toluene over these catalysts. The results showed that HPC were more active and selective for the oxidation of C–H bond of hydrocarbon and have pronounced catalytic activity which depends on reaction temperatures, nature of oxo metal (Mo, Fe) in the primary structure and counter-ion (H3O+, NH4+, Fe3+).

Synthesis and characterization of iron based heteropolyphospho-molybdates The Keggin-type heteropolyacid, modified by exchanging of proton by several counter ions (NH4+, Fe3+) or by substituting of the coordination ion M(VI) by Fe(III), were prepared and characterized by different techniques ( XRD, IR, BET, SEM and TGA/DTGA). The acidic properties were evaluated in the decomposition of isopropanol.

Partial oxidation of methane to formaldehyde and methanol was studied at atmospheric pressure in the temperature range of 700–750 °C using heteropolycompound catalysts (NH4)6HSiMo11FeO40, (NH4)4PMo11FeO39, and H4PMo11VO40, which were prepared and characterized by various analysis techniques such as infrared, visible UV, XRD and DTA. O2 or N2O was used as the oxidizing agent, and the principal products of the reaction were CH3OH, CH2O, CO, CO2, and water. The conversion and the selectivity of products depend strongly on the reaction temperature, the nature of oxidizing agent, and the composition of catalyst.