Ammoxidation Of 2-methylpyrazine Research Articles

Catalytic Performance of Lanthanum Vanadate Catalysts in Ammoxidation of 2-Methylpyrazine

The influence of reaction conditions on the catalytic performance of lanthanum vanadate (La0.1V0.9Ox) catalyst in the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyarazine (CP) has been investigated. This novel catalytic material exhibited remarkably good performance with very high space-time-yields (STY) of CP. The reaction parameters such as the effect of temperature, gas hourly space velocity (GHSV) and all other reaction variables (e.g., NH3, air, and MP feed rates) on the catalytic performance were explored and optimized. For example, an increase in MP feed rate from 2 to >16 mmol/h led to decreased conversion of MP but increased the STY of CP significantly. Optimal performance was achieved when the reaction temperature was 420 °C and the molar ratio of 2-MP, ammonia, air, H2O and N2 in the feed gas was set to 1:7:26:13:22. Under these optimal reaction conditions, the catalyst showed a MP conversion of ~100%, CP selectivity of 86%, and STY of >500 gCP/(kgcat∙h). On the other hand, the formation of pyrazine (Py) as a by-product was found to be high when the NH3:MP ratio was lower at increased contact time. This suggests possible differences in the reaction mechanism pathways with respect to feed composition over La0.1V0.9Ox catalysts.

The Influence of Phosphorous Precursor on the Structure and Ammoxidation Activity of Molybdenum Phosphate Catalysts

Two series of molybdenum phosphate catalysts were synthesized by reacting ammonium heptamolybdate with (1) diammonium hydrogen phosphate and (2) ammonium dihydrogen phosphate. The structural and textural properties of the catalysts, formed during the calcination between 400 and 550 °C, were determined by physico-chemical methods and their catalytic activity evaluated in the ammoxidation of 2-methylpyrazine (MP). The catalysts formed using diammonium hydrogen phosphate displayed higher activity and selectivity during the ammoxidation reaction as compared to those prepared using ammonium dihydrogen phosphate. Formation of a regenerable Mo(OH)3PO4 appears to be responsible for the higher performance of the catalyst.

Tuning the surface composition of novel metal vanadates and its effect on the catalytic performance

Tuning the surface composition of metal vanadates using different cations leads to the development of a new class of highly effective catalysts tested in the ammoxidation of 2-methylpyrazine. Especially, an enrichment of V in the near-surface region is beneficial for improved selectivity. With this approach, a knowledge based optimisation of the catalysts was possible for the first time, which indeed led to highly efficient novel LaVO(x) catalysts with a high yield of 2-cyanopyrazine (≥85%) and extremely high space-time-yields (ca. 525 g kg h(-1)).

Effect of method of preparation on the activity and selectivity of iron phosphate catalyst in the ammoxidation of 2-methyl pyrazine

Ammoxidation of methylpyrazine (MP) to cyanopyrazine (CP) was performed at 633–693 K over iron phosphate catalysts having a P/Fe ratio of 1.2, obtained by adopting different methods of catalyst preparation. The catalysts were characterized by XRD, FTIR, UV-DRS, laser-Raman spectroscopy, TPR, TEM, XPS, acidity by Potentiometric titration and TPD of NH 3. XRD and Raman data suggested predominant formation of quartz phase of iron phosphate. The structure and texture of the catalysts varied with the nature of starting material as well as the preparation method. The catalytic activity depended on the extent of quartz phase formation. Precipitation in the basic medium improved quartz phase formation and enhanced the activity. However, the decreased acid strength caused reduction in nitrile selectivity. A judicious combination of the redox and acid strength properties is required for obtaining maximum yield of CP.

Studies on Preparation, Characterization and Ammoxidation Functionality of Zirconium Phosphate-Supported V2O5 Catalysts

Zirconium pyrophosphate (ZrP2O7) was synthesized from zirconyl chloride and phosphoric acid. A series of ZrP2O7-supported V2O5 catalysts, with the oxide loading ranging from 2 to 8 wt.%, was prepared by wet impregnation method. These catalysts were characterized by various techniques like X-ray diffraction, BET surface area, pore size distribution, FT-IR spectroscopy, acidity measurements and X-ray photoelectron spectroscopy. Their catalytic functionality was evaluated in the ammoxidation of 2-methyl pyrazine (MP) to 2-cyano pyrazine (CP). The V2O5/ZrP2O7 catalysts are found to be highly active and selective. FT-IR profiles of used catalysts indicate the interaction of ammonia with vanadia. The physico-chemical properties of the catalysts are correlated with their activity and nitrile selectivity.

Structure and reactivity of zirconium oxide-supported ammonium salt of 12-molybdophosphoric acid catalysts

A series of catalysts with varying quantities of ammonium salt of 12-molybdophosphoric acid supported on zirconium dioxide was synthesized. The catalysts were characterized by nitrogen adsorption for BET surface area, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and 31P MAS NMR techniques to study the nature of the interactions of the active component with the support as a function of salt loading. The nature of the Keggin ion species (intact, fragmented or decomposed) formed on the support varies with the extent of loading of the heteropolyacid salt. A good correlation was obtained between the extent of formation of lacunary Keggin ion species and the activity of the catalysts during the ammoxidation of 2-methylpyrazine at different reaction temperatures.

In situ synthesis of ammonium salt of 12-molybdophosphoric acid on iron phosphate and the ammoxidation functionality of the catalyst in the transformation of 2-methylpyrazine to 2-cyanopyrazine

The ammonium salt of 12-molybdophosphoric acid (AMPA) on iron phosphate was synthesized via in situ interaction between the phosphate species of the support and the molybdenum component of ammonium heptamolybdate. The concentration of AMPA was varied such that the nominal MoO 3 content of the catalysts was in the range of 5–20 wt.%. The formation of AMPA, possessing the typical Keggin structure, was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. Thermo-gravimetric and differential thermal (TG/DT) analyses were used to establish the stability of these catalysts. Whereas the support, FePO 4, displayed low activity but maximum selectivity to 2-cyanopyrazine (CP), the in situ synthesized catalysts exhibited higher activity during the ammoxidation of 2-methylpyrazine (MP). At lower reaction temperatures and particularly, at lower AMPA loading, the in situ synthesized catalysts have shown higher activity and retained substantially high selectivity.

A comparison of structure and catalytic functionality of 12-molybdophosphoric acid and its ammonium salt in the ammoxidation of 2-methylpyrazine to 2-cyanopyrazine

Two series of catalysts have been prepared by calcination of 12-molybdophosphoric acid or its ammonium salt at various temperatures, in the region of 300–500 °C. The catalysts have been characterized by nitrogen adsorption, XRD, FTIR spectroscopy and TG/DTA analysis to delineate changes in the solid phase associated with high-temperature treatment. Ammoxidation of 2-methylpyrazine has been carried out on these catalysts in a continuous, vapor phase, fixed-bed reactor, in the reaction temperature range of 360–420 °C. The used catalysts have also been subjected to characterization to ascertain the extent of formation of the salt from its decomposition products. The ammonium salt has shown higher activity, selectivity and better stability, when compared with its parent acid, up to a calcination temperature of 450 °C. However, at temperatures higher than the decomposition temperature the activity of the salt decreases considerably, possibly due to the formation of an undesired species mediated by Mo in the reduced state, thus setting a limit to the calcination temperature.

Interaction-induced enhancement in the activity and selectivity of a titania-supported ammonium salt of a 12-molybdophosphoric acid catalyst during ammoxidation of 2-methylpyrazine.

A titania-supported ammonium salt of 12-molybdophosphoric acid has been synthesized, and the salt-support interaction, which enhanced the reaction rate, has been correlated with the activity of the catalyst in the ammoxidation of 2-methylpyrazine.

Influence of ammonium salt formation on the activity and selectivity of the 12-molybdophosphate heteropolyacid catalyst prepared by solid–solid interaction in the ammoxidation of 2-methylpyrazine

The ammonium salt of 12-molybdophosphoric acid has been prepared by the solid-state interaction of the ammonium salts of molybdenum and phosphorus. The catalysts obtained by pretreatment of the precursor at various temperatures, have been characterized by nitrogen adsorption, X-ray diffraction (XRD), Fourier-transformed infrared (FTIR) spectroscopy and temperature-programmed decomposition (TPD) of the catalysts. Ammoxidation of 2-methylpyrazine has been carried out on these catalysts. The amount of ammonium salt present in the catalyst has been correlated with the activity and selectivity of the catalysts.

Ammoxidation of 2-methylpyrazine. Characterisation of catalyst

The effect of changing the relative ratios of the active components in Sb–V–Mn mixed oxides, their concentration on the support and the nature of the latter has been analysed by employing several techniques, such as X-ray diffraction, scanning electron microscopy, electron probe microanalysis and electron spin resonance spectroscopy, together with chemical analysis, a titration of the surface acidity, and determinations of both the B.E.T. surface area and the porosity. A close dependence of activity and selectivity on the nature of the support was observed, connected with the ability of the latter to suppress the formation of microporosity. The catalytic activity is due to Sb4+ species. V and Mn both act as a structural promoter, conferring electrical conductivity on the solid and so improving the rapid electron transfer from the bulk to the surface, and vice versa.

Ammoxidation of 2-methylpyrazine over oxide catalysts

Ammoxidation of 2-methylpyrazine over oxide catalysts

Ammoxidation of 2-methylpyrazine over oxide catalysts

The explorative research and optimisation of the catalyst is reported. Many different mixtures of transition metal oxides were examined, both in the presence and in the absence of steam. Different binders and supports were also tested. The best results were shown by a mixture of Sb/V/Mn oxides, supported on α-alumina, when working at 650–700 K and in the presence of steam. In such conditions, more than 90 mol % conversion and ca. 75 mol % selectivity to 2-cyanopyrazine were obtained, coupled with good durability. The aged catalyst was easily regenerable, by simple reoxidation in controlled conditions.