What are the Applications of Alumina in Catalysis
The function of alumina in the field of catalysis is diverse, and its application as a carrier in industrial catalysis is the most extensive. In addition, some aluminas can also be used as catalysts. As for some alumina hydrates used as binders in the forming of catalysts or carriers, they are further expanded in application as alumina catalyst materials after high-temperature calcination.
1. Alumina as catalyst carrier
Alumina is widely used as a catalyst carrier in fields such as refining, fertilizers, and petrochemicals.
(1) Refining catalyst carrier
Refining catalysts mainly include catalytic cracking catalysts, catalytic reforming catalysts, hydrofining agents, hydrocracking catalysts, reforming pretreatment catalysts, alkylation catalysts, olefin stacking catalysts, ethylene oxide silver catalysts, etc. Catalytic reforming catalysts use γ-alumina as a carrier, mostly spherical, elongated, and cloverleaf-shaped; hydrogenation catalyst carriers mostly use γ-alumina, made into sheets, spheres, elongated shapes, and cloverleaf shapes, with a small amount of SiO added to improve thermal stability. In recent years, both domestic and foreign markets have introduced γ-alumina containing TiO as carriers for hydrofining catalysts; ethylene oxide silver catalysts use α-Al2O3 as carriers; alumina is also partially used in catalytic cracking.
(2) Fertilizer catalyst carriers
Fertilizer catalysts account for the largest amount in chemical catalysts. Sulfur-tolerant wide-temperature conversion catalysts consume the most alumina carriers, all using γ-Al2O3 as carriers, mainly in spherical and elongated forms with great market potential. Methanation catalysts use sheet or spherical y-A103 as carriers. In hydrocarbon steam conversion catalysts, gaseous hydrocarbon conversion mostly uses α-Al2O3 as carriers. Low-temperature conversion, methanol synthesis, and alcohol-synthesis catalysts mostly use CuO·ZnO·Al0 as the main component.
(3) Petrochemical catalyst carriers
Toluene dealkylation to benzene uses elongated γ-Al2O3 loaded with Cr2O3. Ethanol dehydration to ethylene, glycol dehydration to glycol, often uses spherical or elongated γ-Al2O3, with small amounts of additives as catalysts. There are many varieties of hydrogenation catalysts, such as benzene phenol hydrogenation to cyclohexanol, benzene hydrogenation to cyclohexane using γ-Al2O3 nickel carriers, and γ-AL2O used for desulfurization of reforming catalysts. C2 gas phase hydrogenation uses θ–Al2O3 as a carrier, and C3 liquid phase hydrogenation uses δ-Al2O3 as a carrier. Al2O3 is the main component of COS hydrolysis in synthetic gas purification. Dechlorination agents also use γ-Al2O3 as the main component.
2.Alumina as catalyst
Catalysts containing alumina are mostly used as carriers with various active components. There is also a class of catalysts that directly use alumina as the catalyst, or prepare mixed oxide catalysts by combining alumina with other oxides. Claus sulfur recovery catalysts, ethanol dehydration catalysts, methanol dehydration to dimethyl ether, ethanol amination and esterification catalysts are typical examples of γ-Al2O3 used directly as catalysts. A10 and AL0 can be used as catalysts for olefin double bond transfer. Al2O3 can also be synthesized with other oxides to prepare mixed oxide catalysts for mixed use.
3 Alumina as binder
When forming catalysts or catalyst carriers, it is often necessary to add binders as forming aids. Some hydroxides, especially pseudo-boehmite, can act as excellent binders to bind their own particles that are difficult to form but suitable as catalysts, or to bind other catalyst particles that are not suitable for precipitation on the carrier. When alumina is used as a binder, it not only improves the strength of the catalytic material but also the porosity and good heat resistance can adjust the pore structure and heat resistance of the catalyst, and adapt to higher regeneration temperatures. In addition, alumina also has good water resistance, so the catalyst will not break or disintegrate even if it is damp or wet.