JP2005082423A - Zirconia-based oxide and solid acid catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconia-based oxide higher in acid strength and acid content and more excellent in high-temperature stability. <P>SOLUTION: The zirconia-based oxide is an oxide containing zirconium, aluminum, and sulfur. The zirconium and the aluminum are contained in such amounts that the former accounts for 92.0 to 99.6 mol% (as zirconium oxide), and the latter accounts for 0.4 to 8.0 mol% (as aluminum oxide), provided that the total is 100 mol%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel zirconia-based oxide and a solid acid catalyst.

  It has already been known that strong solid acidity is expressed by supporting sulfate ions on zirconium oxide (Non-patent Documents 1 and 2).

  It is also known to use this solid acidity as various catalysts. For example, it has been proposed that a material in which various metal elements are combined with zirconium oxide is used as a solid acid catalyst such as an alkylation reaction or an exhaust gas purification catalyst (Patent Documents 1 to 3).

However, when sulfate ions are supported on zirconium oxide, the acid strength and acid amount of Lewis acid, which are important active sites for use as a catalyst for isomerization reaction, are insufficient. Moreover, the conventional sulfate ion-supported zirconia has a problem that the sulfate ion is decomposed at a relatively low temperature (about 600 ° C.), and the catalytic activity is reduced or deactivated.
JP-A-1-245854 Japanese Patent Laid-Open No. 2-71840 JP-A-4-341325 Arata, Hino, “Preparation of Solid Superacids and Their Surface Properties and Catalysis”, Surface, vol. 19, no. 2 (1981) Arata “Solid Super Strong Acid This Decade”, Catalyst, vol. 31, no. 7, p. 512-517 (1989)

  Accordingly, a main object of the present invention is to provide a zirconia-based oxide having a higher acid strength and an acid amount and an excellent high-temperature stability.

  As a result of intensive studies in view of the problems of the prior art, the present inventor has found that an oxide having a specific composition can achieve the above object, and has completed the present invention.

  That is, the present invention relates to the following zirconia oxide and solid acid catalyst.

1. An oxide containing zirconium, aluminum and sulfur,
Zirconia characterized in that the zirconium and aluminum are contained in a proportion of 92.0 to 99.6 mol% as zirconium oxide and 0.4 to 8.0 mol% as aluminum oxide in a total of 100 mol%. Oxides.

  2. The zirconia oxide according to Item 1, wherein sulfur is contained in an amount of 0.5 to 30.0 mol% as sulfate ions with respect to 100 mol% in total of zirconium oxide and aluminum oxide.

  3. 3. A solid acid catalyst comprising the zirconia oxide according to item 1 or 2.

  4). Item 3. An isomerization reaction catalyst comprising the zirconia oxide according to item 1 or 2.

  5). 3. A paraffinic hydrocarbon isomerization catalyst comprising the zirconia oxide according to item 1 or 2.

  6). Item 3. An isomerization reaction catalyst comprising the zirconia-based oxide according to Item 1 or 2, which is used for an isomerization reaction from n-butane to i-butane.

  In the present invention, the strength of the Lewis acid expressed on the Zr atom can be increased by increasing the positive charge on the Zr atom by combining zirconium oxide and aluminum oxide at a predetermined ratio.

  The mechanism of solid acidity on zirconium oxide (zirconia) supporting sulfuric acid can be shown by a model as shown in FIG. Lewis acid points are given on Zr atoms, and Bronsted acid points are given by surface hydroxyl groups. In general, the acid point showing acidity called super strong acid is considered to be a Lewis acid point, and increasing the positive charge on the Zr atom is the most direct and efficient method for increasing the acidity of the Lewis acid point. It is.

  In the present invention, by combining aluminum oxide, the positive charge on the Zr atom is increased as in the model shown in FIG. This fact is demonstrated by examining the change in binding energy (observation of chemical shift by XPS) as shown in FIG. The results in FIG. 3 show the difference in binding energy depending on the firing temperature of the oxide synthesized in the examples described later. In particular, it can be seen that among the oxides fired at 873 K (= 600 ° C.), SAZ3 and SAZ5 exhibit strong binding energy.

  In the present invention, the amount of acid can be increased by combining zirconium oxide and aluminum oxide to suppress the crystal growth of zirconium oxide and to secure a high specific surface area. In FIG. 4, the difference in the inhibitory effect of the crystal growth by the difference in the aluminum content rate in the oxide of the below-mentioned Example is shown. It can be seen that the presence of the predetermined aluminum suppresses crystal growth.

  Further, the composite charge according to the present invention can increase the positive charge on the Zr atom. As a result, the supported sulfate ion can be stably present at a higher temperature (in particular, a high temperature of 600 ° C. or higher).

  According to the oxide of the present invention, zirconium oxide and aluminum oxide are complexed at a predetermined ratio, and since sulfate ions exist, relatively high acid strength and acid amount can be maintained up to a high temperature. Can do. Therefore, the oxide of the present invention is particularly effective as a solid acid catalyst. For example, it can be applied as a catalyst for isomerization reaction, alkylation reaction, hydrolysis reaction and the like in the field of organic synthesis.

1. Zirconia-based oxide The zirconia-based oxide of the present invention is an oxide containing zirconium, aluminum and sulfur, and the zirconium and aluminum are 92.0 to 99.6 mol% as zirconium oxide and 0 as aluminum oxide. It is characterized in that it is contained in a proportion of 100 to 100 mol% in total of 4 to 8.0 mol%.

  The oxide of the present invention is basically a mixed oxide of zirconium oxide and aluminum oxide.

The content ratios of zirconium and aluminum are respectively zirconium oxide and aluminum oxide as a total amount of 100 mol%, and usually zirconium oxide: aluminum oxide = 92.0 to 99.6 mol%: 0.4 to 8.0 mol% Zirconium oxide: aluminum oxide = 92.5-99.3 mol%: 0.7-7.5 mol%, more preferably zirconium oxide: aluminum oxide = 93.2-98.8 mol%: 1. 2 to 6.8 mol%. When the content ratio as aluminum oxide exceeds 8.0 mol%, the conversion rate decreases, and when it is less than 0.4 mol%, the decomposition temperature of SO ₄ decreases, which is not preferable.

  The content ratio of sulfur (sulfate radical) can be appropriately determined according to the composition of the oxide of the present invention, usage, usage, etc., but with respect to a total of 100 mol% of zirconium oxide and aluminum oxide (that is, as an outer shell), It is desirable to contain 0.5 to 30.0 mol% (especially 5.0 to 15.0 mol%) of sulfate ions. When sulfur in such a range is contained, better solid acidity and the like can be exhibited.

  The oxide of the present invention may contain other components (for example, rare earth elements) or unavoidable impurities within a range not impeding the effects of the present invention.

The oxide of the present invention can be applied to various uses, but is particularly useful as a catalyst (solid acid catalyst). Therefore, it can be suitably used for reactions in which a conventional solid acid catalyst is used, for example, isomerization reaction, alkylation reaction, polymerization reaction and the like. In particular, the oxide of the present invention is also suitable as a catalyst for isomerization reaction of paraffinic hydrocarbons (for example, isomerization of n-butane to i-butane).
2. Production method of zirconia-based oxide The production method of the oxide of the present invention is not particularly limited as long as the predetermined composition defined in the present invention is obtained, and is performed according to a known method such as a liquid phase method or a solid phase method. can do.

  For example, a) a method in which a precipitate obtained by coprecipitation using a mixed solution containing zirconium ions and aluminum ions is impregnated with a sulfate ion-containing solution, and then the obtained impregnated body is fired, b) a zirconium compound Examples include a method of impregnating an aluminum ion-containing solution (zirconium hydroxide, basic zirconium salt, etc.) and further impregnating a sulfate ion-containing solution, and then firing the obtained impregnated body.

  In the present invention, the oxide of the present invention can be suitably obtained particularly by the method a).

  In the case of producing according to the method a), the mixed solution can be prepared by respectively using soluble salts of zirconium and aluminum and dissolving them in a suitable solvent (preferably water).

  Examples of the soluble salt of zirconium include zirconium chloride, nitrate, sulfate, acetate, and the like. More specifically, zirconium oxychloride, zirconium nitrate, zirconium acetate, zirconium sulfate and the like can be used.

  Examples of the soluble salt of aluminum include chlorides, nitrates, sulfates and acetates. More specifically, aluminum nitrate, aluminum acetate or the like can be used.

  In the present invention, any of these anhydrides and hydrates can be used as these zirconium and aluminum salts.

  The mixed solution may be prepared by adding a soluble zirconium salt and an aluminum soluble salt to one solvent, or a zirconium soluble salt solution and an aluminum soluble salt solution. After preparing separately, you may prepare a mixed solution by mixing both solutions.

  The concentration of zirconium and aluminum in the mixed solution is not particularly limited as long as the ratio of zirconium and aluminum is adjusted so as to be the content ratio of the oxide of the present invention. That is, the concentration may be adjusted so that the ratio of zirconium oxide and aluminum oxide becomes the above content ratio.

  Furthermore, when the third component is contained in the oxide of the present invention, the mixed solution may contain ions of the third component. For example, it may be added to the mixed solution in the form of a compound containing a third component (for example, an inorganic acid salt, an organic acid salt, etc.), or a third component solution may be prepared in advance and added to the mixed solution.

  Next, a precipitate is formed from the mixed solution. For example, by adding an alkali agent (ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, etc.), the pH of the mixed solution is adjusted to an alkaline region (preferably pH 7-9), thereby adjusting zirconium and aluminum. A precipitate is formed as the contained hydroxide. The alkaline agent is usually preferably added as an aqueous solution. The concentration of the aqueous solution is not particularly limited as long as the pH can be adjusted, but is usually about 5 to 30% by weight, preferably 20 to 25% by weight.

  The generated precipitate may be solid-liquid separated according to a known method such as filtration or centrifugation, and then washed with water as necessary. Furthermore, you may dry at the temperature of 150 degrees C or less as needed.

  The obtained precipitate is impregnated with a sulfate ion-containing solution. As the sulfate ion-containing solution, a solution of sulfuric acid or a soluble sulfate (preferably an aqueous solution) can be suitably used. As the soluble sulfate, for example, ammonium sulfate and other ammonium hydrogen sulfate can be used. The sulfate ion concentration of the sulfate ion-containing solution is not limited, but is usually 5.0 to 20.0% by weight. Moreover, what is necessary is just to adjust suitably the impregnation amount of the sulfate ion containing solution with respect to a precipitate so that the sulfur content in the oxide obtained may become said content as a sulfate ion.

  In the present invention, if necessary, after impregnating the sulfate ion-containing solution, the impregnated precipitate may be dried at 150 ° C. or lower.

  The oxide of the present invention can be obtained by firing after the impregnation. The firing temperature is not limited, but is generally 400 to 800 ° C, preferably 500 to 700 ° C. The firing time may be appropriately determined depending on the firing temperature or the like. Further, the firing atmosphere may be either air or an oxidizing atmosphere.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

Example 1
Zirconium oxychloride aqueous solution (99.2 with Zr as zirconium oxide)
g) and an aqueous aluminum nitrate solution (containing 0.8 g of Al as aluminum oxide), adjusted to pH 8 with 25% aqueous ammonia, and stirred for 2 hours to produce a composite hydroxide gel. After solid-liquid separation, the solid content was washed with 2000 g of water. The obtained gel was dried at 100 ° C. overnight to obtain a composite hydroxide. The composite hydroxide was impregnated with an aqueous ammonium sulfate solution (containing 4.5 g of S) and then dried at 110 ° C. The obtained dried product was fired at 650 ° C. to obtain an oxide (SAZ1).

Example 2
An oxide (SAZ2) was obtained in the same manner as in Example 1 except that an aqueous zirconium oxychloride solution (containing 97.5 g of Zr as zirconium oxide) and an aqueous aluminum nitrate solution (containing 2.5 g of Al as aluminum oxide) were used. It was.

Example 3
An oxide (SAZ5) was obtained in the same manner as in Example 1, except that an aqueous solution of zirconium oxychloride (containing 95.8 g of Zr as zirconium oxide) and an aqueous solution of aluminum nitrate (containing 4.2 g of Al as aluminum oxide) were used. It was.

Comparative Example 1
An oxide (SAZ10) was obtained in the same manner as in Example 1, except that an aqueous solution of zirconium oxychloride (containing 91.6 g of Zr as zirconium oxide) and an aqueous solution of aluminum nitrate (containing 8.4 g of Al as aluminum oxide) were used. It was.

Comparative Example 2
An oxide (SAZ20) was obtained in the same manner as in Example 1 except that an aqueous zirconium oxychloride solution (containing 82.9 g of Zr as zirconium oxide) and an aqueous aluminum nitrate solution (containing 17.1 g of Al as aluminum oxide) were used. It was.

Comparative Example 3
An oxide (SAZ0) was obtained in the same manner as in Example 1 except that an aqueous solution of zirconium oxychloride (containing 100 g of Zr as zirconium oxide) was used and an aqueous aluminum nitrate solution was not used.

Test example 1
Various physical properties were examined using the oxides of the examples and comparative examples. Table 1 shows the composition, SO ₄ decomposition temperature, bond energy, conversion rate and selectivity of each oxide.

（１）結合エネルギーの変化
各酸化物におけるＺｒ３ｄ_5/2の結合エネルギーの変化を焼成温度（６７３Ｋ、８７３Ｋ及び１０７３Ｋ）ごとにそれぞれ調べた。測定装置は、アルバック・ファイ社製「PHI 5800 ESCA SYSTEM」を使用した。その結果を図３に示す。
（２）結晶成長抑制効果
アルミニウムの含有割合による結晶成長の抑制効果を調べた。各酸化物を焼成温度（８７３Ｋ、９７３Ｋ及び１０７３Ｋ）ごとにＸ線回折分析を行った。その結果を図４に示す。図４に示すように、アルミニウム添加量の増加に伴い高温でもテトラゴナル相が維持されていることから、本発明品が高温まで結晶成長が抑制されていることがわかる。
（３）熱分解温度
アルミニウムの含有割合による硫酸イオンの熱分解温度の変化を調べた。測定装置は、理学電機株式会社「Thermo Plus 2 TG8120」を用いた。その結果を図５に示す。アルミニウムの添加によりＳＯ₄の脱離に伴う重量減少が高温側にシフトしていることからＳＯ₄の熱安定性が向上していることがわかる。
（４）Ｓ＝Ｏ間の振動の観察
ＩＲによりＳＯ₄のピークの観察を行った。その結果を図６に示す。アルミニウムの担持によりＳ＝Ｏ間のピ−ク位置が低角側にシフトしていることが確認できる。このことからＳ＝Ｏ間の結合力が強まることによりジルコニウム上の電子が引き寄せられ、その結果としてジルコニウムの正電荷が高まっていることがわかる。
（５）ルイス酸点及びブレンステッド酸点の測定
ピリジン吸着ＩＲによりルイス酸点及びブレンステッド酸点の測定を行った。測定は、８７３Ｋで前処理したものについて、３７３Ｋ及び５７３Ｋの温度下でそれぞれ行った。その結果を図７に示す。図７より、アルミニウムを添加したＳＡＺは５７３Ｋ熱処理後でも酸点に起因するピリジンのピーク強度が大きいことから高温での酸点の熱安定性に優れることがわかる。特にＳＡＺ５及びＳＡＺ３が安定なことがわかる。
（６）触媒活性及び初期活性
各酸化物の存在下でｎ−ブタンからｉ−ブタンへの転化反応を行い、その転化率及び選択率を調べた。反応装置は、固定床流通式の反応装置を用いた。反応条件は、温度３３８Ｋ ・圧力０．１ＭＰａとし、ｎ−ブタンの供給量を０．２５ｍｌ／ｍｉｎとして、触媒活性の経時変化を測定した。その結果を図８に示す。

(1) Change in bond energy The change in bond energy of Zr3d _5/2 in each oxide was examined for each firing temperature (673K, 873K, and 1073K). As a measuring apparatus, “PHI 5800 ESCA SYSTEM” manufactured by ULVAC-PHI was used. The result is shown in FIG.
(2) Crystal growth inhibitory effect The crystal growth inhibitory effect by the aluminum content was investigated. Each oxide was subjected to X-ray diffraction analysis at each firing temperature (873K, 973K, and 1073K). The result is shown in FIG. As shown in FIG. 4, since the tetragonal phase is maintained even at high temperatures as the amount of aluminum added increases, it can be seen that the crystal growth of the product of the present invention is suppressed to high temperatures.
(3) Thermal decomposition temperature The change in the thermal decomposition temperature of sulfate ion according to the aluminum content was examined. As a measuring apparatus, Rigaku Corporation “Thermo Plus 2 TG8120” was used. The result is shown in FIG. It can be seen that the thermal stability of SO ₄ is improved because the weight loss accompanying the desorption of SO ₄ is shifted to the high temperature side due to the addition of aluminum.
(4) Observation of vibration between S = O The peak of SO _{4 was} observed by IR. The result is shown in FIG. It can be confirmed that the peak position between S = O is shifted to the low angle side due to the loading of aluminum. From this, it can be seen that electrons on zirconium are attracted by increasing the binding force between S = O, and as a result, the positive charge of zirconium is increased.
(5) Measurement of Lewis acid point and Bronsted acid point The Lewis acid point and Bronsted acid point were measured by pyridine adsorption IR. The measurement was carried out at a temperature of 373K and 573K for the sample pretreated at 873K. The result is shown in FIG. From FIG. 7, it can be seen that SAZ added with aluminum is excellent in thermal stability of acid sites at high temperatures since the peak intensity of pyridine due to acid sites is large even after heat treatment at 573K. In particular, it can be seen that SAZ5 and SAZ3 are stable.
(6) Catalytic activity and initial activity A conversion reaction from n-butane to i-butane was carried out in the presence of each oxide, and the conversion rate and selectivity were examined. As the reaction apparatus, a fixed bed flow type reaction apparatus was used. The reaction conditions were a temperature of 338 K, a pressure of 0.1 MPa, a supply amount of n-butane of 0.25 ml / min, and the change in catalyst activity with time was measured. The result is shown in FIG.

  FIG. 9 shows the relationship between the alumina addition ratio and the initial activity (conversion rate). From this, it can be seen that a particularly high conversion can be obtained with an alumina addition amount of 0.7 to 7.5 mol%.

It is a schematic diagram which shows a mode that an acid point expresses. It is a schematic diagram which shows the effect by containing of aluminum. It is a figure which shows the change of the binding energy by addition of aluminum. It is a figure which shows the inhibitory effect (baking temperature 873K, 973K, and 1073K) of the crystal growth by addition of aluminum. It is a figure which shows the change of the thermal decomposition temperature of a sulfate ion by addition of aluminum. It is a diagram showing a result of observation of the peak position of the SO ₄ by IR. It is a figure which shows the measurement result (373K and 573K) of the Lewis acid point and Bronsted acid point by pyridine adsorption IR. It is a figure which shows the result of the catalytic activity test of the oxide obtained by the Example and the comparative example. It is a figure which shows the relationship between the addition ratio of aluminum (in aluminum oxide conversion), and initial stage activity (conversion rate).

Claims (4)

An oxide containing zirconium, aluminum and sulfur,
Zirconia characterized in that the zirconium and aluminum are contained in a proportion of 92.0 to 99.6 mol% as zirconium oxide and 0.4 to 8.0 mol% as aluminum oxide in a total of 100 mol%. Oxides. The zirconia-based oxide according to claim 1, wherein sulfur is contained in an amount of 0.5 to 30.0 mol% as sulfate ions with respect to 100 mol% in total of zirconium oxide and aluminum oxide. A solid acid catalyst comprising the zirconia-based oxide according to claim 1. A catalyst for isomerization reaction comprising the zirconia-based oxide according to claim 1 or 2.

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