LUDOX Catalyst Brochure

LUDOX® Colloidal Silica Catalyst Applications LUDOX® Colloidal Silica - Catalyst Applications LUDOX® colloidal silicas have been used for many years to manufacture catalysts for fluid cracking, emissions control, and a variety of chemical syntheses. Most commonly, they offer excellent binding power and high temperature stability. Further, the chemical inertness of sintered silica enables catalytic activity to be maximized. LUDOX® colloidal silica products are known for their consistent quality, narrow particle size distribution, purity and, in some grades, low sodium levels. Grace provides extensive sales and technical service support, and offers research and development support. What is LUDOX® Colloidal Silica? Colloidal silica is an important industrial product that is manufactured from the simplest of ingredients, sand and water. However, its useful properties are far from commonplace. LUDOX® colloidal silicas are discrete nanoscale spherical particles of amorphous silica dispersed in water. In addition to being extremely durable, stable, and heat-tolerant, these particles can be tailor-made and chemically customized to yield enormous potential. LUDOX® colloidal silica is manufactured by W. R. Grace & Co. Since its introduction to the market in 1948, manufacturers from diverse industries have found a variety of ways to utilize colloidal silica in their products and processes. The silica surface contains silanol groups that are weakly acidic. Most products are provided at alkaline pH, so that some silanol groups are de-protonated. As a result, a negative charge exists on the particle surface. When this charge is balanced with counterions at an appropriate ionic strength, the colloidal particles are electrostatically stabilized to keep the particles from reacting with each other and aggregating. In + + grades commonly used in catalysts, the counterions are usually sodium (Na ) or ammonium (NH4 ) ions. While many other forms of amorphous silica are milled from large aggregates, colloidal silica is grown from sodium silicate to a given target particle size. The conditions of the growth process determine the particle size and distribution. Typical size offerings in Grace’s product line are 5, 7, 12 and 22 nanometers. All sols after particle growth contain sodium counterions. To make low sodium products, the sodium counterions are removed by deionization and replaced with ammonium counterions. Counterion + + OH Na or NH4 Si O− O O OH O Si Si O O O O Figure 1. The reactivity of colloidal silica is enabled by the silanol groups and its high specific surface area. grace.com | 2 LUDOX® Colloidal Silica - Catalyst Applications General Properties LUDOX® colloidal silicas have a proven track record of high performance in many catalytic applications. Refer to Table 1 for a listing of grades and their properties. Products are distinguished by their nominal particle size, specific surface area, silica concentration (%SiO2), + + and stabilizing counterions (Na or NH4 ). All of these products are designed to be monomodal with a narrow particle size distribution. Conceptually, the narrow distribution should enable nearly uniform reactivity. The particle size values in Table 1 are nominal values, and specific surface area is used as a specification property. Particle size and surface area are related geometrically, and small size or high surface area are associated with high reactivity. ® ® Product names often contain the target %SiO2 value. For example, LUDOX AS-40 colloidal silica contains 40% SiO2 and LUDOX AS-30 colloidal silica contains 30% SiO2. Generally, a higher silica content enables a formulation with a higher solids content. In other circumstances, the formulator may seek the higher specific surface area of LUDOX® AS-30 colloidal silica for a more attrition-resistant structure. In many catalysts, sodium is a poison and must be minimized. While sodium silicate can be used to make some catalysts, its high sodium level (approximately 21% relative to silica) prevents its use in many others. LUDOX® AS-30 colloidal silica products with sodium counterions typically contain 0.5-2.0% sodium relative to silica, depending on particle size. Even lower sodium levels can be attained by replacing sodium counterions with ammonium. LUDOX® Colloidal Silica Properties Typical Sodium Nominal Particle Size Specific Surface Area Silica Content LUDOX® Grade Counterions Content (nm) (m2/g SiO ) %SiO 2 2 (Wet Basis) %Na SM-AS 7 360 25 0.05 + AS-30 NH4 12 230 30 0.06 AS-40 22 140 40 0.07 HSA 12 230 30 0.10 H+ TMA 22 130 34 0.10 FM 5 435 15 0.30 SM 7 360 30 0.50 LS 12 230 30 0.10 Na+ HS-30 12 230 30 0.30 HS-40 12 230 40 0.40 TM-50 22 130 50 0.30 Table 1. LUDOX® colloidal silicas commonly used in catalyst applications. grace.com | 3 LUDOX® Colloidal Silica - Catalyst Applications The Role of Colloidal Silica in Catalysts LUDOX® colloidal silica is generally used in catalyst applications to: OH OH OH • Provide the silica component of the catalyst support, zeolite, OH or molecular sieve OH OH • Bind the components of the catalyst together • Improve adhesion to substrates OH OH • Improve physical properties (hardness, attrition resistance, etc.) H O OH • Stabilize catalytic activity O The high purity and controlled particle size of LUDOX® colloidal H O H O 2 silica make it an effective source of silica for zeolite synthesis. The 2 colloidal silica particles are at least partially dissolved in the alkaline O H O synthesis mix, and when combined with an alumina source, can OH crystallize into the desired alumino-silicate zeolite structures. O In another application, the colloidal silica functions to bind other catalyst components together, constituting a small percentage of the final catalyst. Chemically, surface silanol groups interact with either surface silanols of other silica particles or with surface metal hydroxides of other catalyst components. Figure 2. Bonding progression between two colloidal silica With drying and calcination, water is eliminated via a condensation particles. Only silanol groups involved in bonding are depicted. reaction so that stable Si-O-Si or Si-O-metal bonds are formed. As Because the particles are multifunctional, each particle can react the reaction progresses, individual particles fuse together as shown with more than one particle resulting in aggregates and gels. in Figure 2. Individual particles eventually fuse together. Similarly, colloidal silica can attach to larger metal oxide particles (e.g., clays, zeolites, etc.) as depicted in Figure 3. In the wet state, the O metal oxide particles are surrounded by the colloidal silica particles. O O O On drying, the colloidal silica particles attach and bond to the metal O O O O oxide particles and fuse together with heat. After the catalyst is O made, it can be bonded to a substrate by the same mechanism. In addition, some catalysts contain silica as the predominant support constituent which provides a high surface area anchor for the active catalyst components. The above mentioned functions are not fully distinct from one Colloidal Silica another. When used as a silica source, for example, colloidal silica Bonding with Metal Oxides also binds both the silica particles and catalytic components together. Colloidal silica in washcoat formulations not only binds Metal Metal Oxide Oxide the components of the washcoat but also will help bind those Particle Particle components to the substrate. After the colloidal silica reacts with the catalytic particles and Colloidal Silica substrates, it is chemically and thermally stable. Particles Figure 3. Colloidal silica particles bind metal oxide particles together. Binding occurs between silica particles and metal oxide particles. grace.com | 4 LUDOX® Colloidal Silica - Catalyst Applications Examples of Catalyst Applications The following examples are taken from U.S. patents and are presented to illustrate typical applications. Silica Source for Zeolites Zeolites are microporous aluminosilicate crystalline structures that contain channels or cavities that can selectively adsorb molecules based on their size and shape. A number of zeolite types are important in industrial scale catalytic processes. LUDOX® colloidal silicas provide a very useful source of silica, a key raw material for zeolite synthesis. In this application, colloidal silica particles may be mostly dissolved or transformed in the presence of an alumina source to form the aluminosilicate or phosphoaluminosilicate zeolite. A recent review by Dusselier and Davis of zeolite synthesis provides an overview of industrially significant small pore zeolites and their syntheses. One very important industrial scale zeolite is Zeolite Y, used in the fluid catalytic cracking process. In Union Carbide’s U.S. Patent 3,130,007, processes are disclosed to make Zeolite Y (depicted in Figure 4). In one example, sodium aluminate solution, sodium hydroxide, and colloidal silica were mixed together and heated at 100°C for 21 hours to crystallize the product, which was then separated by filtration and dried. The product was identified as Zeolite Y by its X-Ray diffraction pattern and composition. Grace recommends LUDOX® HS-40 colloidal silica for this application, which forms pure Zeolite Y while other silica sources (sodium silicate, silica gel, fused silica) produce Zeolite Y contaminated with other crystalline components. Other industrially significant zeolites are of the chabazite structure type, namely SSZ-13 and SAPO-34. The former zeolite is a widely used catalyst support in mobile emission control as a selective catalytic reduction catalyst, to reduce nitrogen oxides from combustion gases. The SAPO-34 zeolite is also a widely used catalyst support for the Methanol to Olefins (MTO) process. The synthesis of SAPO-34 was first patented by Union Carbide Corporation, as disclosed in the examples in U.S. Patent 4,440,871 beginning with Example 34. In these examples, use of a 30% colloidal silica sol is disclosed. Later, a method for Figure 4. Zeolite Y structure. making SAPO-34 zeolite was given in ExxonMobil Chemical’s U.S. Patent 6,897,180 in which a mixture of boehmite powder, water, phosphoric acid, LUDOX® AS-40 colloidal silica, morpholine and zeolite chabazite seeds was prepared.

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