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Active Surface Area by Chemisorption
Catalysts are used in a variety of applications from the production of consumer goods to the protection of the environment. Optimum design and efficient utilization of catalysts require a thorough understanding of the surface structure and surface chemistry of the active material.
Chemical adsorption (chemisorption) analysis techniques provide much of the information necessary to evaluate catalyst materials in the design and production phases, as well as after a period of use. Catalytic activity is evaluated by measuring the amounts and types of reactive gas adsorbed. This volume of gas, along with an understanding of the reaction stoichiometry, is used to calculate metal dispersion, active surface area, size of crystallites, and surface acidity.
Micromeritics instruments are specifically designed for the highly aggressive environment present during chemisorption analysis. Internal components are constructed of highest-quality stainless steel to prevent reactivity with most commonly used chemisorptives. Heated manifolds, gas lines, and detectors are provided to allow analysis with condensable vapors. Sample preparation occurs in situ to prevent contamination prior to analysis. Samples can be prepared at high temperatures (up to 1100 deg C) and at low pressures (<10 -5 mmHg). Features
Two Independent vacuum systems that allow preparation and analysis to proceed concurrently,
Oil-free “dry” vacuum option to prevent oil contamination
Two-station intelligent degas system for fully automated degassing with controlled heating time profiles, an extra long duration cryogen system for unattended analyses,
Twelve gas inlets that are automatically selectable to allow for automated selection of pretreatment, backfill, and analysis gases, and the ability to connect to a mass spectrometer.
Technique Overview
The basics of the analytical technique are simple; a sample contained in an evacuated sample tube is cooled (typically) to cryogenic temperature, then is exposed to analysis gas at a series of precisely controlled pressures. With each incremental pressure increase, the number of gas molecules adsorbed on the surface increases. The pressure at which adsorption equilibrium occurs is measured and the universal gas law is applied to determine the quantity of gas adsorbed.
As adsorption proceeds, the thickness of the adsorbed film increases. Any micropores in the surface are quickly filled, then the free surface becomes completely covered, and finally larger pores are filled. The process may continue to the point of bulk condensation of the analysis gas. Then, the desorption process may begin in which pressure systematically is reduced resulting in liberation of the adsorbed molecules. As with the adsorption process, the changing quantity of gas on the solid surface is quantified. These two sets of data describe the adsorption and desorption isotherms. Analysis of the isotherms yields information about the surface characteristics of the material.
A Short Bibliography of Researchers Using Micromeritics’ Gas Sorption Analyzers to Study Metal Organic Frameworks
Making Plastics Ecologically Friendly - Introduction of Biorenewable CO2 into the Polymerization Process With the Help of Micromeritics Materials Characterization Instruments
Major Accessory Literature:
Vapor Option / Water Vapor Option
* High Vacuum Systems
** Micropore Systems
In keeping with a policy of ongoing product improvement, specifications are subject to change without notice.
 Link to: CUSTOM ENGINEERED PRODUCTS
Since the 1960's Micromeritics has been modifying standard products and accessories to accommodate special needs. We have now expanded this service to include custom-designed analyzers and accessories.
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A Note About 32- and 64-Bit Windows and Micromeritics' Software
Micromeritics products are designed to operate in most Microsoft Windows environments. However, more current versions of Microsoft Windows, specifically the 64-bit version of Windows 7, lack some of the services once offered by Microsoft. Because of this, Micromeritics applications will not operate with 64-bit operating systems. Micromeritics software applications are directly compatible with 32-bit version operating systems only. In cases where a 64-bit operating system may be corporate-required or essential for running other software programs, Virtual PC software and a 32-bit operating system should be installed on the host computer (64 bit) as a guest operating system. This will allow proper installation and operation of the Micromeritics application. |