Upon modification of V 2 O 5 with SnO 2 or ZrO 2 , increase in the activity and selectivity of the vanadium-oxide catalyst in the vapor-phase oxidation of 3-methylpyridine into nicotinic acid were observed. It was shown that the promoting effects of SnO 2 and ZrO 2 were the result of increases under their influence of the proton affinity of the vanadyl oxygen and decreases in the enthalpy of deprotonation of the methyl group of the substrate, connected by a nitrogen atom with the Lewis acidic center (vanadium ion). The given characteristics were calculated by the density functional theory quantum-chemical method. Modification of binary V 2 O 5-SnO 2 and V 2 O 5-ZrO 2-catalysts by TiO 2 addition resulted in a further increase in the nucleophility of the vanadyl oxygen and, as a consequence, an increase in the catalytic activity and selectivity for nicotinic acid formation.

An effect of some metal oxides on the polymorphic transformation of anatase into rutile and on the rate of dissociation of V 2 O 5 in the systems V 2 O 5 -TiO 2 and V 2 O 5 -TiO 2 -Me x O y has been studied, where Me x O у is SnO 2 , WO 3 , Cr 2 O 3 or ZrO 2 .

Modifi cation of V 2 O 5 with Ti, Sn, Zr, Nb, and Al oxides improves the activity and selectivity of the vanadium oxide catalyst in vapor-phase oxidation of β-picoline to give nicotinic acid. It is shown that the conversion of β-picoline and the yield of nicotinic acid on two-component V 2 O 5 -TiO 2 , V 2 O 5 -SnO 2 , V 2 O 5 -ZtrO 2 , V 2 O 5 -Nb 2 O 5 , and V 2 O 5 -Al 2 O 3 catalysts may be several times those on the V 2 O 5 catalyst. It was found that, on passing from V 2 O 5 to double-component vanadium-containing catalysts, the proton affi nity of active oxygen bonded to vanadium, calculated by the quantum-chemical method, grows simultaneously with the increase in the activity of the catalysts in the oxidation reaction.Pyridine-carboxylic acids and their derivatives possess various physiological properties and fi nd wide application in medicine and agriculture. An important place among carboxylic acids of the pyridine series is occupied by nicotinic acid used to obtain cordiamin, feramide, nicodan, ethiacin, vitamin PP, and other medicinal preparations [1]. Nicotinic acid is also used to prepare premixes in animal breeding. Nicotinic acid is produced by liquid-phase oxidation of β-picoline by inorganic oxidizing agents or by hydrolysis of nicotinic acid nitrile formed in oxidative ammonolysis of the starting methyl pyridine [2].The vapor-phase catalytic oxidation of β-picoline with atmospheric oxygen, which yields nicotinic acid in a single stage, is strongly complicated by the instability of pyridine-carboxylic acids and their rapid decarboxylation at comparatively low temperatures [3]. The conversion of β-picoline on chromium orthovanadate at 350°C was only 19%, and the formation selectivities of pyridine-3-aldehyde and nicotinic acid, 39.5 and 49.1%, respectively. Among the catalysts with general formula Cr 1-x Al x VO 4 , the system Cr 0.5 Al 0.5 VO 4 has the highest activity, with the conversion of 3-methylpyridine at the same reaction temperature being 80% and the overall yield of nicotinic acid and pyridine-3-aldehyde reaching a value of 69% (overall selectivity 86%) [4]. In [5], the mechanism of oxidation of isomeric picolines on this catalyst was studied by the in situ DRIFTS method and the Mars-Van-Krevelen mechanism was substantiated. Among the disadvantages of the cited studies should be mentioned the incomplete conversion of β-picoline, presence of pyridine-3-aldehyde contaminating nicotinic acid in reaction products, and lack of systematic analyses of the effect of various oxides on the catalytic activity of V 2 O 5 .The vapor-phase catalytic oxidation of β-picoline to nicotinic acid has been the subject of a number of publications [6][7][8]. The research has been focused on fi nding effective catalysts providing an increase in the yield of nicotinic acid at comparatively low temperatures. The effect of the composition of a catalyst on its catalytic action in oxidation of β-picoline has been considered [4,9]. A brief review of publications in this fi eld can be found in [10].

No abstract

Catalytic properties of vanadium-titanium-tin oxides catalysts of various compositions were studied in oxidative ammonolysis of 3-and 4-methylpyridines.Heterogeneous catalytic oxidation by atmospheric oxygen is the main way for oxidative processing of petrochemical and coking hydrocarbon raw materials into oxygen-containing organic compounds. The reaction of oxidative ammonolysis is a catalytic reaction of hydrocarbons with atmospheric oxygen and ammonia belong to promising industrial methods for synthesis of valuable nitrogen-containing organic half-products and monomers [1].The reactions of oxidation and oxidative ammonolysis of alkyl aromatic compounds are purposively studied at Bekturov Institute of Chemical Sciences Joint-Stock Company. Particular attention is being given to development of catalysts determining the degree and selectivity of conversion of raw materials into appropriate target products. For example, the catalytic activity of a number of multicomponent vanadium oxide catalysts modifi ed with oxides of Group IV and VI metals in oxidative ammonolysis of 3-and 4-methylpyridines has been studied. Catalysts developed for this process on the basis of vanadium, tin, and titanium oxides are highly effi cient: the oxidative ammonolysis of methylpyridines occurs with high conversion of starting substances [2]. The optimal conditions, in which target products can be obtained in >90% yield, have been determined for synthesis of pyridinecarboxylic acid nitriles. It has been found that, to achieve a high selectivity of nitrile formation, the process of oxidative ammonolysis on V-Ti-Sn-O oxides catalysts should be performed with 5-10 mol of ammonia per mole of starting substances, which raises the ammonia concentration in effl uent gases and makes the process more technologically intricate. The excess of ammonia and high temperature occasionally lead to a spontaneous rise in temperature and enhance oxidative destruction processes, which diminishes the formation selectivity of the target products. In addition, these catalysts operate at high temperatures (360-400°C), the conversion of the starting substances being low at moderate temperatures. Therefore, a search for new active and selective catalysts capable of operating at lower temperatures at a minimum amount of ammonia was conducted.It is known [3] that ammonia can be oxidized by several pathways, and the nature of a catalyst and the process conditions (temperature, composition of the ammonia-air mixture, contact duration, and other factors) affect the degree and selectivity of ammonia conversion. Previously, the composition of ammonia oxidation products formed on vanadium oxide catalysts modifi ed with titanium and tin oxides have been studied and it was found that ammonia is oxidized on the catalysts under study to give N 2 , N 2 O, and NO 2 . It was shown that, selecting the molar ratio between oxygen