Mamoru Ai

Characteristics of heteropoly compounds as catalysts for selective oxidation

Abstract As catalysts for selective oxidation, heteropoly compounds such as 12-molybdophosphoric acid (H 3 PMo 12 O 40 ) and its salts have been investigated, in relation to the acidic property, the contribution of bulk acid, the effect of steam in the feed gas, the thermal stability, the effect of countercations, and the oxidation activity and selectivity. It was found that, though the heteropoly compounds are different in several physical characteristics from ordinary mixed metal oxides, the catalytic actions can be understood, to a great extent, from the acid-base properties much as in the case of mixed-oxide catalysts.

The oxidation activity and acid-base properties of SnO2-based binary catalysts: I. The SnO2V2O5 system

The amounts of both the acidic and basic sites of a series of SnO2ue5f8V2O5 catalysts with different compositions were measured by studying the adsorption of the basic and acidic molecules in the gas phase, using both the static and pulse methods. The acidities of the catalysts are fairly low in the low range of V2O5 content (V < 20 atom%); the acidity per unit of weight shows a maximum at about V = 40–50 atom%, but the acidity per unit of surface area increases continuously with the V2O5 content. On the other hand, the pure SnO2 has a fair basicity, and the introduction of a smal amount of V2O5 (V = 2–20 atom%) to SnO2 remarkably enhances the basicity. It can be said that the SnO2-rich (V < 20 atom%) catalysts are basic, while the V2O5-rich catalysts are acidic. The vapor-phase oxidation of 1-butene and butadiene, the isomerization of 1-butene, and the dehydration and dehydrogenation of isopropyl alcohol (IPA) were carried out in the presence of an excess of air, and the relationship between the catalytic behavior and the acid-base properties was investigated. It was concluded that the activities and selectivities can be relatively well explained by the acid-base properties between the catalyst and the reactant.

Oxidation of propane to acrylic acid on V2O5&P2O5-based catalysts

Abstract V 2 O 5 ue5f8P 2 O 5 -based oxides were found to be effective as catalysts for the partial oxidation of propane, using gaseous oxygen as an oxidant. Acrylic acid was the sole product other than carbon oxides. The best results for the formation of acrylic acid are obtained with this Te/P/V atomic ratio; 0.10−0.15/1.15/1 oxide catalysts. The yield of acrylic acid attains 10.5 mol%. As the extent of the reaction increases, the selectivity steadily decreases, while the yield first increases and then attains a maximum at a propane conversion of about 50%. The rate of reaction increases with an increase in the concentrations of both oxygen and propane, while it remains almost unchanged with the addition of water vapor to the feed gas. On the other hand, for the formation of acrylic acid, higher concentrations of oxygen and water vapor, a lower concentration of propane, and a lower reaction temperature are found to be favorable.

The oxidation activity and acid-base properties of SnO2-based binary catalysts: II. The SnO2MoO3 and SnO2P2O5 systems

The vapor-phase oxidation of 1-butene, butadiene, and acetic acid, the isomerization of 1-butene, and the dehydration and dehydrogenation of isopropyl alcohol (IPA) were carried out, in the presence of an excess of air, over two series of catalysts, SnO2ue5f8MoO3, and SnO2ue5f8P2O5, and the relationship between the catalytic behavior and the acid-base properties of the catalysts was investigated. The acidity and the basicity of the SnO2ue5f8MoO3 catalysts were measured by studying the adsorption of basic and acidic molecules, respectively, in the gas phase, using both the static and pulse methods. The acidities of the SnO2ue5f8MoO3 catalysts are dramatically high at the Mo content of 30–60 atom%, though those of the SnO2-rich (Mo 80 atom%) catalysts are fairly low. The basicity is remarkably enhanced by the introduction of a small amount of MoO3 (Mo < 5 atom%). It can be said that the catalysts are basic in the MoO3-poor composition. In the case of the SnO2ue5f8P2O5 catalysts, the acidity and basicity were evaluated from the catalytic activity for the dehydration of IPA to propylene and the (dehydrogenation rate for IPA)/(dehydration rate for IPA) ratio, respectively. The introduction of P2O5 increases the acidity and decreases the basicity, to a very small extent, so it cannot cause a remarkable modification in the catalytic behavior; that is, the SnO2ue5f8P2O5 catalysts are rather basic.

The acid-base properties of MoO3Bi2O3P2O5 catalysts and their correlation with catalytic activity and selectivity

Abstract The amounts of both the acidic and basic sites of MoO 3 ue5f8Bi 2 O 3 ue5f8P 2 O 5 catalysts over a full range of Bi Mo ratios were measured by studying the adsorption of basic and acidic molecules, respectively, in the gas phase. The results obtained by the pulse method agreed well with those obtained by the static method. The acidity of pure Bi 2 O 3 is far lower than that of MoO 3 ue5f8P 2 O 5 , and with an increase in the Bi 2 O 3 content, the acidity rapidly increases at first, passes through a maximum at the Bi Mo atomic ratio of 1–2, and then decreases. On the other hand, the basicity of MoO 3 ue5f8P 2 O 5 is fairly low compared with that of pure Bi 2 O 3 ; the basicity of the catalyst gradually increases with the Bi 2 O 3 content. The relationship between the acid-base properties obtained here and the catalytic behavior obtained previously was investigated. The oxidation and isomerization activities for olefins are proportional to the acidity of the catalyst, and the oxidation activity for an acidic compound and hydrogen is connected with the basicity. The selectivity of the catalyst was also interpreted in connection with the acid-base properties. Finally, the characters of the active sites were discussed, together with those of the acidic and basic sites.

Catalytic activity for the oxidation of methanol and the acid-base properties of metal oxides

The vapor-phase oxidation of methanol was carried out in the presence of an excess of air over many series of composite oxide catalysts, the acidity and basicity of which had been previously determined, such as MoO3ue5f8TiO2, MoO3ue5f8Fe2O3, MoO3ue5f8SnO2, MoO3ue5f8P2O3, MoO3ue5f8Bi2O3ue5f8P2O6, V2O5ue5f8MoO3, WO3- and U3O8-based oxides, SnO2ue5f8K2O, Co3O4ue5f8K2O, and Bi2O3ue5f8XnOm (X = P, Mo, W, V, and S), and the relationship between the catalytic behavior and the acidbase properties of the metal oxides was investigated. Formaldehyde can be obtained only from such acidic oxides as MoO3, WO3, V2O5, and U3O8, but not from oxides which are more basic than TiO2, e.g., TiO2, Fe2O3, SnO2, Bi2O3, ZnO, and Co3O4. A clear correlation always exists between the activity for formaldehyde formation and the acidity in the cases of the MoO3- or V2O5-containing catalysts, and the amounts of the by-products are small, except in the case of the MoO3ue5f8SnO2. Methanol is dehydrated preferentially to ether over the WO3ue5f8P2O5 (PW = 298–2080) catalysts, and no correlation exists between the activity for formaldehyde formation and the acidity. Over the basic oxides, methanol is oxidized mainly to CO2, and the activity for CO2 formation is correlated with the basicity of the catalysts. It is concluded that the activation of methanol by acidic sites is a necessary condition for the formation of formaldehyde, that the possibility of this methanol activation mainly decides the oxidation activity, and that the combination of metal oxides contributes to the enhancement or modification of the acidic property.

Activities for the decomposition of formic acid and the acid-base properties of metal oxide catalysts

Abstract Studies have been made to ascertain whether the catalytic activity for the oxidative dehydrogenation of formic acid to CO2 is effective as an index of the basicity of metal oxides, which are used as oxidation catalysts. The basicity of the catalysts was measured by means of the adsorption of CO2 and of acetic acid and by titration with benzoic acid. The decomposition of formic acid was carried out in the presence of an excess of air using a continuous-flow reaction system, in order to obtain data for the valence states of the metal oxide which were at a steady state. With such basic oxides as SnO2ue5f8K2O, ZnOue5f8K2O, Bi2O3ue5f8K2O, Bi2O3ue5f8MoO3, and Bi2O3ue5f8P2O5, only the oxidative dehydrogenation to form CO2 and H2O takes place, and the catalytic activity for this reaction is well correlated with the basicity. With acidic oxides such as WO3ue5f8P2O5, TiO2ue5f8MoO3, and SnO2ue5f8MoO3, only the dehydration to CO takes place, and the activity for this reaction is correlated with the acidity. Then, the catalytic activities for the dehydration and oxidative dehydrogenation were measured systematically using various kinds of single and mixed metal oxide catalysts. A clear regularity between the catalytic behavior of the metal oxides and their acid-base properties was found. It is concluded that, as an index of basicity of solid catalysts, the catalytic activity for the oxidative dehydrogenation of formic acid is effective for rather basic catalysts, while the (dehydrogenation activity for isopropyl alcohol, IPA)/(dehydration activity for IPA) ratio is valid for rather acidic catalysts.

Vapor-phase aldol condensation of formaldehyde with acetic acid on V2O5P2O5 catalysts

Abstract V 2 O 5 ue5f8P 2 O 5 binary oxides with P V atomic ratios from 1.06 to 1.2 were found to be effective as catalysts for the aldol-type condensation of formaldehyde (HCHO) with acetic acid to form acrylic acid. As the source of HCHO, 37% formalin or trioxane was employed. In the case of trioxane, the yield of acrylic acid attained about 98 mol%, based on the charged HCHO with the acetic acid/HCHO molar ratio of 2.5. On the other hand, in the case of formalin, the yield attained about 75 mol%, and methyl acetate and methyl acrylate were also formed by the esterification of the acids with methanol present in the formalin. The main side-reaction is the decomposition of acetic acid to form acetone and CO 2 . This side-reaction is greatly accelerated over acrylic acid formation by an elevation of the temperature. The rates of both reactions were found to be inhibited by water vapor. The reactions of HCHO with derivatives of acetic acid, such as methyl acetate and acetaldehyde, were also Studied.

The production of methyl formate by the vapor-phase oxidation of methanol

Methanol is oxidized to methyl formate, but not to formaldehyde, over SnO/sub 2/-MoO/sub 3/ catalysts. Tests of various binary-oxide catalysts indicated that the best results for both activity and selectivity were obtained with the Sn/Mo atomic ratio = 7/3 catalyst. It was proposed that methyl formate is formed via formaldehyde as follows: 2 CH/sub 3/OH ..-->.. 2 HCHO ..-->.. HCOOCH/sub 3/. It was concluded that the possession of both acidic and basic properties is required to catalyze the reaction.

The activity of WO3-based mixed-oxide catalysts: I. Acidic properties of WO3-based catalysts and correlation with catalytic activity

The numbers of acidic sites in the WO3ue5f8P2O5 binary system with different PW ratios and in the WO3ue5f8P2O5ue5f8XnOm ternary system (XnOm consists of different kinds of oxides) were determined by three methods, namely, a static method, a gas chromatographic-pulse technique, and a titration method. The values for acidity, obtained by studying the adsorption of NH3 or pyridine from the gas phase, are consistent with those obtained by the titration method. Pure WO3 is fairly low in acidity, but the introduction of P2O5 increases the acidity and a maximum occurs at P = 10–20 atom%. The addition of a third component to WO3-P2O5 (PW = 28), in small amounts, decreases the acidity, except in the case of Cr2O3, where it increases the acidity. The relationship between the acidity and the catalytic activities for the dehydration of isopropyl alcohol, the isomerization of 1-butene, and the decomposition of cumene was investigated. It was found that the acidic function of the catalysts is the factor deciding the catalytic activities for these reactions.