JP4156142B2 - Catalyst carrier - Google Patents
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- JP4156142B2 JP4156142B2 JP25861699A JP25861699A JP4156142B2 JP 4156142 B2 JP4156142 B2 JP 4156142B2 JP 25861699 A JP25861699 A JP 25861699A JP 25861699 A JP25861699 A JP 25861699A JP 4156142 B2 JP4156142 B2 JP 4156142B2
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- 239000003054 catalyst Substances 0.000 title claims description 27
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 38
- 239000000843 powder Substances 0.000 claims description 35
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims description 31
- 230000007704 transition Effects 0.000 claims description 25
- 229910010271 silicon carbide Inorganic materials 0.000 claims description 23
- 239000011812 mixed powder Substances 0.000 claims description 8
- 239000013078 crystal Substances 0.000 claims description 5
- 238000002474 experimental method Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 239000002245 particle Substances 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 5
- 239000011777 magnesium Substances 0.000 description 5
- 238000002156 mixing Methods 0.000 description 5
- 239000002243 precursor Substances 0.000 description 5
- 229910052749 magnesium Inorganic materials 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical group [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 description 3
- 229910052788 barium Inorganic materials 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical group CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 2
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 description 2
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 2
- 238000007084 catalytic combustion reaction Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 2
- 239000005350 fused silica glass Substances 0.000 description 2
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052863 mullite Inorganic materials 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 229910052596 spinel Inorganic materials 0.000 description 2
- 239000011029 spinel Substances 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- MXRIRQGCELJRSN-UHFFFAOYSA-N O.O.O.[Al] Chemical compound O.O.O.[Al] MXRIRQGCELJRSN-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- -1 aluminum alkoxide Chemical class 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000004332 deodorization Methods 0.000 description 1
- 238000007580 dry-mixing Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 150000002604 lanthanum compounds Chemical class 0.000 description 1
- JLRJWBUSTKIQQH-UHFFFAOYSA-K lanthanum(3+);triacetate Chemical compound [La+3].CC([O-])=O.CC([O-])=O.CC([O-])=O JLRJWBUSTKIQQH-UHFFFAOYSA-K 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Description
【０００１】
【発明の属する技術分野】
本発明は、自動車の排ガス浄化、触媒燃焼等の触媒担持体に関する。
【０００２】
【従来の技術】
従来、触媒を用いて化学反応・燃焼・脱臭等を行う際、その反応接触点を多く確保するため、ハニカム形状の触媒担体に無機質粉末からなる触媒担持体を塗布し、更にそれぞれの反応に適した貴金属等の触媒を担持したものが使用されている。そして、その触媒担持体としては、高比表面積のγアルミナが多く用いられているが、このものは９００℃以上の温度でα−アルミナに転移し、比表面積が急激に小さくなるため、自動車の排ガス、触媒燃焼等、比較的高温で反応を行わせる用途においては、触媒機能が低下する問題があった。
【０００３】
これを解決するため、特開平５−４０５０号公報には、硫酸アルミニウムとバリウムの化合物から得られる耐熱性遷移アルミナが提案されている。しかし、この遷移アルミナを得るには、原料として硫酸アルミニウムを用いるため副生する大量の硫化物等を処理する必要がある。
【０００４】
また、特開平９−２５１１９号公報には、アルミナ水和物にランタン化合物（硝酸ランタン）を含浸乾燥後、気流粉砕器で粉砕し、その後加熱により耐熱遷移アルミナを製造する方法が提案されているが、この方法においては、高価な酢酸ランタン、硝酸ランタン等が必要である。
【０００５】
更には、特開平１０−１５２３２０号公報では、マグネシウム含有の遷移アルミナ粉末を触媒担持体とする提案がある。しかしながら、この方法においても、Ｍｇ化合物を２０００℃以上の温度で加熱気化させなければそれを製造することができなかったので、非常に高価なものとなった。
【０００６】
以上のように、上記３方法のいずれの場合も、遷移アルミナの形成前に、比表面積低下抑制剤としてのバリウム、ランタンあるいはマグネシウムを気相で添加し高度に分散させなければ製造することができず、生産性に劣るものであった。そこで、９００℃以上の高温下における使用においても、比表面積の低下が少ない、しかも安価なアルミナ粉末の出現が待たれていた。
【０００７】
【発明が解決しようとする課題】
本発明は、上記状況に鑑みてなされたものであり、その目的は、低コストにして、高温下においても比表面積が著しく低下しない触媒担持体を提供することである。
【０００８】
【課題を解決するための手段】
すなわち、本発明は、比表面積２０ｍ２／ｇ以上の炭化ケイ素超微粉と遷移アルミナ粉末とを含有する混合粉末からなることを特徴とする触媒担持体である。本発明においては、炭化ケイ素超微粉の比表面積が３０〜１００ｍ２／ｇであり、それを１〜４０重量％含有してなり、残部が実質的に遷移アルミナ粉末であることが好ましい。更に、炭化ケイ素超微粉の結晶型がβ型であり、その平均真円度が０．８５以上であることが好ましい。
【０００９】
【発明の実施の形態】
本発明における遷移アルミナとは、加熱によりαアルミナ、スピネル、ムライト等の高温安定型のアルミナ系結晶に転化する物質をいう。アルミナの場合、高温安定型はα型であり、遷移アルミナはγ、δ、θ型がよく知られており、これらの混合物であっても良い。本発明において、α型の含有は全く否定するものではなく、Ｘ線回折法で測定されたαアルミナは、全アルミナ中、１０重量％まで含まれていても良い。
【００１０】
遷移アルミナの粉末度は、１００ｍ２／ｇ以上であることが好ましい。
【００１１】
遷移アルミナ粉末は、遷移アルミナ前駆物質を加熱することによって製造することができる。遷移アルミナ前駆物質の一例を示せば、アルミニウムの水酸化物、アルミニウムアルコキシド等である。製造の容易さと価格を考慮すると、水酸化アルミニウムが最適である。
【００１２】
遷移アルミナ前駆物質には、加熱によって、最終アルミナ系物質がスピネル、ムライトあるいはこれらの混合物となり、しかも高温下の使用によって著しい比表面積の低下を起こさない程度に、例えばＳｉ、Ｍｇ等の水酸化物などの化合物を含有させることもできる。
【００１３】
本発明における炭化ケイ素超微粉とは、通常の炭化ケイ素粉末が有する５〜１５ｍ２／ｇ程度の比表面積よりも高い比表面積を有する炭化ケイ素粉末を意味し、２０ｍ２／ｇ以上の比表面積を有する炭化ケイ素粉末のことである。
【００１４】
本発明おいて、炭化ケイ素超微粉は、９００℃以上の高温下の使用において、遷移アルミナ粉末の著しい比表面積の低下を防止し、触媒担持体としての機能を持続させるために用いられるものである。その粉末度は、微細なものほど好ましいが、比表面積２０ｍ２／ｇ以上、特に２５〜１５０ｍ２／ｇ、更に好ましくは３０〜１００ｍ２／ｇ程度であることが良い。
【００１５】
また、炭化ケイ素の結晶型には種々あるが、本発明においては、β型が上記遷移アルミナの比表面積低下防止効果に優れる。全炭化ケイ素中、β型の含有率は、Ｘ線回折法の測定に基づき、５０重量％以上、特に７０重量％以上であることが好ましい。
【００１６】
更には、炭化ケイ素超微粉の形状は、その球形度合を平均真円度で表示して、０．８５以上、特に０．９以上であることが好ましい。平均真円度は、走査型電子顕微鏡（日本電子社製「ＪＳＭ−Ｔ２００型」）と画像解析装置（日本アビオニクス社製）を用い、以下のようにして測定することができる。
【００１７】
すなわち、先ず、粉末のＳＥＭ写真から粒子の投影面積（Ａ）と周囲長（ＰＭ）を測定する。周囲長（ＰＭ）に対応する真円の面積を（Ｂ）とすると、その粒子の真円度はＡ／Ｂとして表示できる。そこで、試料粒子の周囲長（ＰＭ）と同一の周囲長を持つ真円を想定すると、ＰＭ＝２πｒ、Ｂ＝πｒ２であるから、Ｂ＝π×（ＰＭ／２π）２ となり、個々の粒子の真円度は、真円度＝Ａ／Ｂ＝Ａ×４π／（ＰＭ）２として算出することができるので、任意に選ばれた２０００個の粒子の平均値として求めらることができる。
【００１８】
本発明における炭化ケイ素超微粉は、例えば気相合成法によって製造することができる（特開昭６０−９０８０９号公報参照）。すなわち、金属Ｓｉと溶融シリカの混合粉を加熱してＳｉＯガスを発生させ、それとアセチレンとを１５００〜２０００℃の温度で接触させることによって製造することができる。
【００１９】
本発明の触媒担持体は、高比表面積の遷移アルミナと上記炭化ケイ素超微粉との所定量を混合することによって製造することができる。混合は、ボールミル等を用いた乾式混合でもよいが、湿式法によれば両粉末の均一性に優れたものとなる。
【００２０】
また、本発明の触媒担持体は、遷移アルミナ前駆物質と炭化ケイ素超微粉との混合物を熱処理することによっても製造することができる。すなわち、例えば水酸化アルミニウム粉末等の遷移アルミナ前駆物質と炭化ケイ素超微粉とを、水、イソプロピルアルコール等の溶剤を媒体とした濃度３０〜６０重量％程度のスラリーを調製し、それを酸化性雰囲気中、温度２００〜８００℃程度で熱処理することによって製造することができる。この方法によれば、遷移アルミナ粉末内部に炭化ケイ素超微粉が取り込まれたような状態の混合粉末が製造されるので、９００℃以上の高温下の使用において、遷移アルミナ粉末の低比表面積化が一段と防止された触媒担持体となる。
【００２１】
触媒担持体中の炭化ケイ素超微粉の含有割合は、特に限定されないが、１〜４０重量％であることが好ましい。特に好ましくは２〜２０重量％、更に好ましくは３〜１５重量％である。
【００２２】
本発明の触媒担持体には、遷移アルミナ粉末、炭化ケイ素超微粉以外に、Ｂａ、Ｍｇ等のアルカリ土類元素、Ｌｎ、Ｃｅ等の希土類元素、Ｓｉ、Ｔｉ等の酸化物等が含有されていても良い。
【００２３】
本発明の触媒担持体を、自動車排ガス触媒等の触媒担持体と使用すれば、その９００℃以上の高温下における使用であるにもかかわらず、触媒機能を長く持続させることができる。
【００２４】
【実施例】
金属Ｓｉと溶融シリカをモル比で１：１となるように計量し、４４μｍ以下に粉砕し混合粉を得た。この混合粉を１９００℃に加熱してＳｉＯガスを発生させ、それを別室に導き、ＳiＯガスとアセチレンとを１５００〜２０００℃の温度範囲内で温度を変えて種々接触させ、超微粉炭化ケイ素を含有する気相生成物を得た。次いで、この気相生成物を空気中７００℃で酸化処理を行った後、フッ酸及び硝酸を用いて酸処理を行い、表１及び表２に示される種々の炭化ケイ素超微粉を製造した。得られた炭化ケイ素超微粉のＸ線回折による結晶型は、いずれもβ型であった。
【００２５】
上記炭化ケイ素超微粉又は市販の炭化ケイ素粉末（昭和電工社製「ＤＵＡ−１」平均粒子径０．４５μｍ、比表面積１５ｍ２／ｇ)と、市販のγアルミナ粉末（住友化学工業社製「ＡＫＰ１５」比表面積１５０ｍ２／ｇ)とを、表１及び表２に示される種々の割合で混合し、混合粉末（触媒担持体）を製造した。
【００２６】
混合は、「乾式」、「湿式」又は「合成」で行った。ここで、「乾式」とは、ボールミルで２時間混合したものであり、「湿式」とは、水を用いてスラリー状にしたものをボールミルで２時間混合、その後濾過時に凝集を防止するため、水をアセトンに置換し乾燥したものである。また、実験Ｎｏ１７に示す「合成」とは、γアルミナに代えて水酸化アルミニウムと実験Ｎｏ２で製造された炭化ケイ素超微粉とをＡｌ２Ｏ３／ＳｉＣの重量比が９５／５となるように計量し、水を加えて固形分３０重量％程度のスラリーを調製し、それを乾燥・粉砕後、４００℃で仮焼したものである。
【００２７】
得られた混合粉末（触媒担持体）を、空気中１１００℃、１２００℃で２４時間加熱し、ＢＥＴ法により、比表面積の変化を測定した。それらの結果を表１、表２に示す。
【００２８】
実験Ｎｏ１、９、１０は比較例、それ以外の実験Ｎｏは本発明例に相当するものである。すなわち、実験Ｎｏ１はγアルミナのみ、実験Ｎｏ９は超微粉炭化ケイ素のみの例であり、いずれも高温加熱によって比表面積が著しく低下した。また、実験Ｎｏ１０は、炭化ケイ素超微粉の代わりに市販の炭化ケイ素粉末（平均粒子径０．４５μｍ、比表面積１５ｍ２／ｇ)を用いたこと以外は、実験Ｎｏ４と同様に行ったものであるが、これまた著しく比表面積が低下した。これらに対し、本発明例はいずれも高温加熱によっても著しい比表面積の低下はなかった。
【００２９】
【表１】
【表２】
【発明の効果】
本発明によれば、高温下の使用においても比表面積の著しい低下のない、遷移アルミナ粉末と炭化ケイ素超微粉を含有してなる触媒担持体が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention, exhaust gas purification of automobiles, about the catalyst support of the catalytic combustion, and the like.
[0002]
[Prior art]
Conventionally, when a catalyst is used for chemical reaction, combustion, deodorization, etc., a catalyst carrier made of inorganic powder is applied to a honeycomb-shaped catalyst carrier in order to secure many reaction contact points. A catalyst carrying a catalyst such as a noble metal is used. As the catalyst carrier, γ-alumina having a high specific surface area is often used. However, this material is transferred to α-alumina at a temperature of 900 ° C. or higher, and the specific surface area rapidly decreases. In applications where the reaction is carried out at a relatively high temperature, such as exhaust gas and catalytic combustion, there has been a problem that the catalytic function is lowered.
[0003]
In order to solve this problem, JP-A-5-4050 proposes a heat-resistant transition alumina obtained from a compound of aluminum sulfate and barium. However, in order to obtain this transition alumina, since aluminum sulfate is used as a raw material, it is necessary to treat a large amount of sulfides by-produced.
[0004]
Japanese Patent Application Laid-Open No. 9-25119 proposes a method of impregnating and drying a lanthanum compound (lanthanum nitrate) in an alumina hydrate, pulverizing with an airflow pulverizer, and then producing heat-resistant transition alumina by heating. However, this method requires expensive lanthanum acetate, lanthanum nitrate, or the like.
[0005]
Furthermore, Japanese Patent Application Laid-Open No. 10-152320 proposes using a magnesium-containing transition alumina powder as a catalyst carrier. However, even in this method, the Mg compound cannot be produced unless it is heated and vaporized at a temperature of 2000 ° C. or higher, so that it is very expensive.
[0006]
As described above, any of the above three methods can be produced unless barium, lanthanum or magnesium as a specific surface area reduction inhibitor is added in the gas phase and highly dispersed before the formation of transition alumina. It was inferior in productivity. Therefore, even when used at a high temperature of 900 ° C. or higher, the appearance of an alumina powder that is low in specific surface area and inexpensive is awaited.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst carrier that is low in cost and whose specific surface area does not significantly decrease even at high temperatures .
[0008]
[Means for Solving the Problems]
That is, the present invention is a catalyst carrier comprising a mixed powder containing a silicon carbide ultrafine powder having a specific surface area of 20 m 2 / g or more and a transition alumina powder. In the present invention, it is preferred that the silicon carbide ultrafine powder has a specific surface area of 30 to 100 m 2 / g, contains 1 to 40% by weight thereof, and the balance is substantially transition alumina powder . Furthermore, it is preferable that the crystal form of the silicon carbide ultrafine powder is β-type, and the average roundness thereof is 0.85 or more .
[ 0009 ]
DETAILED DESCRIPTION OF THE INVENTION
The transition alumina in the present invention refers to a substance that is converted to a high-temperature stable type alumina-based crystal such as α-alumina, spinel, mullite by heating. In the case of alumina, the high temperature stable type is α type, and the transition alumina is well known as γ, δ, θ type, and may be a mixture thereof. In the present invention, the inclusion of α-type is not denied at all, and α-alumina measured by the X-ray diffraction method may be contained up to 10% by weight in the total alumina.
[ 0010 ]
The fineness of the transition alumina is preferably 100 m 2 / g or more.
[ 0011 ]
The transition alumina powder can be produced by heating the transition alumina precursor. An example of the transition alumina precursor is aluminum hydroxide, aluminum alkoxide or the like. In view of ease of manufacture and cost, aluminum hydroxide is optimal.
[ 0012 ]
As the transition alumina precursor, hydroxide such as Si, Mg, etc. is used so that the final alumina-based material becomes spinel, mullite or a mixture thereof by heating, and does not cause a significant decrease in specific surface area due to use at high temperature. Etc. can also be contained.
[ 0013 ]
The silicon carbide ultrafine powder in the present invention means a silicon carbide powder having a specific surface area higher than a specific surface area of about 5 to 15 m 2 / g which a normal silicon carbide powder has, and has a specific surface area of 20 m 2 / g or more. It is the silicon carbide powder which has.
[ 0014 ]
In the present invention, the silicon carbide ultrafine powder is used for preventing the decrease of the specific surface area of the transition alumina powder and maintaining the function as a catalyst support when used at a high temperature of 900 ° C. or higher. . Its fineness is preferably as those fine, the specific surface area of 20 m 2 / g or more, particularly 25~150m 2 / g, more preferably it may be about 30 to 100 m 2 / g.
[ 0015 ]
Moreover, although there are various crystal types of silicon carbide, in the present invention, the β type is excellent in the effect of preventing the specific surface area of the transition alumina from being lowered. The content of β-type in the total silicon carbide is preferably 50% by weight or more, particularly 70% by weight or more based on the measurement by X-ray diffraction method.
[ 0016 ]
Furthermore, it is preferable that the shape of the silicon carbide ultrafine powder is 0.85 or more, particularly 0.9 or more, when the degree of sphericity is expressed as an average roundness. The average roundness can be measured as follows using a scanning electron microscope (“JSM-T200 type” manufactured by JEOL Ltd.) and an image analyzer (manufactured by Nippon Avionics Co., Ltd.).
[ 0017 ]
That is, first, the projected area (A) and the perimeter (PM) of the particles are measured from the SEM photograph of the powder. When the area of a perfect circle corresponding to the perimeter (PM) is (B), the roundness of the particle can be displayed as A / B. Therefore, assuming a perfect circle having the same circumference as the sample particle (PM), PM = 2πr and B = πr 2 , so that B = π × (PM / 2π) 2 , and each particle Since the roundness of can be calculated as roundness = A / B = A × 4π / (PM) 2 , it can be obtained as an average value of 2000 particles arbitrarily selected.
[0018]
The ultrafine silicon carbide powder in the present invention can be produced, for example, by a gas phase synthesis method (see JP-A-60-90809). That is, it can be produced by heating a mixed powder of metal Si and fused silica to generate SiO gas and bringing it into contact with acetylene at a temperature of 1500 to 2000 ° C.
[ 0019 ]
The catalyst carrier of the present invention can be produced by mixing a predetermined amount of transition alumina having a high specific surface area and the above silicon carbide ultrafine powder. The mixing may be dry mixing using a ball mill or the like, but according to the wet method, both powders are excellent in uniformity.
[ 0020 ]
The catalyst carrier of the present invention can also be produced by heat-treating a mixture of a transition alumina precursor and silicon carbide ultrafine powder. That is, for example, a slurry having a concentration of about 30 to 60% by weight using a transition alumina precursor such as aluminum hydroxide powder and silicon carbide ultrafine powder in a solvent such as water and isopropyl alcohol as a medium is prepared in an oxidizing atmosphere. In the inside, it can manufacture by heat-processing at the temperature of about 200-800 degreeC. According to this method, a mixed powder in a state in which silicon carbide ultrafine powder is taken into the transition alumina powder is produced, so that the transition alumina powder has a low specific surface area when used at a high temperature of 900 ° C. or higher. The catalyst carrier is further prevented.
[ 0021 ]
Although the content rate of the silicon carbide ultrafine powder in the catalyst carrier is not particularly limited, it is preferably 1 to 40% by weight. Particularly preferred is 2 to 20% by weight, and more preferred is 3 to 15% by weight.
[ 0022 ]
In addition to the transition alumina powder and silicon carbide ultrafine powder, the catalyst carrier of the present invention contains alkaline earth elements such as Ba and Mg, rare earth elements such as Ln and Ce, and oxides such as Si and Ti. May be.
[ 0023 ]
If the catalyst carrier of the present invention is used with a catalyst carrier such as an automobile exhaust gas catalyst, the catalyst function can be maintained for a long time despite its use at a high temperature of 900 ° C. or higher.
[ 0024 ]
【Example】
Metal Si and fused silica were weighed to a molar ratio of 1: 1 and pulverized to 44 μm or less to obtain a mixed powder. This mixed powder is heated to 1900 ° C. to generate SiO gas, which is led to a separate chamber, and SiO gas and acetylene are brought into contact with each other at various temperatures within a temperature range of 1500 to 2000 ° C. A gas phase product containing was obtained. Next, the vapor phase product was oxidized in air at 700 ° C. and then acid-treated with hydrofluoric acid and nitric acid to produce various silicon carbide ultrafine powders shown in Tables 1 and 2. The crystal form of the obtained silicon carbide ultrafine powder by X-ray diffraction was β type.
[ 0025 ]
The above-mentioned silicon carbide ultrafine powder or commercially available silicon carbide powder (“DUA-1” average particle size 0.45 μm, specific surface area 15 m 2 / g manufactured by Showa Denko KK) and commercially available γ-alumina powder (“AKP15 manufactured by Sumitomo Chemical Co., Ltd.) And a specific surface area of 150 m 2 / g) were mixed at various ratios shown in Tables 1 and 2 to produce a mixed powder (catalyst support) .
[ 0026 ]
Mixing was performed “dry”, “wet” or “synthesis”. Here, “dry type” means mixing for 2 hours in a ball mill, and “wet type” means mixing a slurry of water using a ball mill for 2 hours, and then preventing aggregation during filtration. Water is replaced with acetone and dried. “Synthesis” shown in Experiment No. 17 refers to aluminum hydroxide instead of γ-alumina and silicon carbide ultrafine powder produced in Experiment No. 2 so that the weight ratio of Al 2 O 3 / SiC is 95/5. Weighing, adding water to prepare a slurry with a solid content of about 30% by weight, drying and grinding it, and calcining at 400 ° C.
[ 0027 ]
The obtained mixed powder (catalyst carrier) was heated in air at 1100 ° C. and 1200 ° C. for 24 hours, and the change in specific surface area was measured by the BET method. The results are shown in Tables 1 and 2.
[ 0028 ]
Experiments Nos. 1, 9, and 10 correspond to comparative examples, and other experiment Nos correspond to examples of the present invention. That is, Experiment No1 is an example of γ alumina only, and Experiment No9 is an example of ultrafine silicon carbide only. Experiment No10 was performed in the same manner as Experiment No4, except that a commercially available silicon carbide powder (average particle size 0.45 μm, specific surface area 15 m 2 / g) was used instead of silicon carbide ultrafine powder. However, the specific surface area also significantly decreased. On the other hand, in all of the inventive examples, the specific surface area did not significantly decrease even when heated at high temperature.
[ 0029 ]
[Table 1]
[Table 2]
【The invention's effect】
According to the present invention, there is provided a catalyst carrier comprising a transition alumina powder and a silicon carbide ultrafine powder, which does not significantly decrease the specific surface area even when used at high temperatures.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25861699A JP4156142B2 (en) | 1999-09-13 | 1999-09-13 | Catalyst carrier |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25861699A JP4156142B2 (en) | 1999-09-13 | 1999-09-13 | Catalyst carrier |
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| Publication Number | Publication Date |
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| JP2001079414A JP2001079414A (en) | 2001-03-27 |
| JP4156142B2 true JP4156142B2 (en) | 2008-09-24 |
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| JP25861699A Expired - Fee Related JP4156142B2 (en) | 1999-09-13 | 1999-09-13 | Catalyst carrier |
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| WO2009085870A2 (en) | 2007-12-19 | 2009-07-09 | Saint-Gobain Ceramics & Plastics, Inc. | Aggregates of alumina hydrates |
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