Abstract
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.
Highlights
The heterogeneously catalyzed ammoxidation is a selective oxidation of olefins and methyl aromatics, respectively, that is carried out in the presence of ammonia, leading to commercially valuable nitriles [1,2]
Olefins or methyl aromatics and hetero aromatics can be used as feed; in this regard, the ammoxidation of 2-methylpyrazine (MP) belongs to this group of reactions
We have examined the effect of various metals (Al, Fe, Cr, Nb, La, Bi) in metal vanadate (MVs) catalysts (e.g., AlVO4, FeVO4, CrVO4, NbVO5, LaVO4, and BiVO4)
Summary
The heterogeneously catalyzed ammoxidation is a selective oxidation of olefins and methyl aromatics (or hetero aromatics), respectively, that is carried out in the presence of ammonia, leading to commercially valuable nitriles [1,2]. The reaction follows a Mars-van Krevelen mechanism, i.e., nucleophilic oxygen is introduced into an activated allyl or benzyl species forming an oxygen-containing intermediate [5,6] Such an intermediate interacts with ammonia adsorbed on the catalyst surface, forming an imine that is further dehydrated to a nitrile [7]. Olefins or methyl aromatics and hetero aromatics can be used as feed; in this regard, the ammoxidation of 2-methylpyrazine (MP) belongs to this group of reactions. It allows the manufacture of 2-cyanopyrazine (CP) in a single step and is an industrially important reaction as well.
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