Mesopore and Micropore Surface Characterization Analysis

The new 3Flex Surface Characterization Analyzer from Micromeritics is a fully automated, three-station device that can perform highly accurate, high throughput surface area and pore size analyses with superior resolution and MicroActive data reduction.

It is possible to upgrade each analysis station from mesopore to micropore with its own transducers for existing or future high-throughput needs.

Figure 1. 3Flex Surface Characterization Analyzer from Micromeritics

Features of 3Flex Surface Characterization Analyzer

With its three configurable analysis stations and smaller footprint, a single 3Flex saves costs associated with the use of multiple instruments and additional bench space.

Moreover, users can benefit from the significantly reduced analysis time provided by the 3Flex when compared to a single or two-station equipment.

Micropore ports incorporate krypton capability for the analysis of very low surface area materials. The capability to analyze heated vapor is standard, with an optional capability of extended-range vapor analysis.

The design features of the 3Flex ensure its superior performance and are the next step in surface characterization analyzers.

The novel instrument is equipped with isothermal jacket technology and a new larger dewar design to provide consistent temperature control for many hours, an essential condition for micropore analyses. It also boasts data reduction features, improved software capabilities, and instrument monitoring.

A novel dashboard monitors and facilitates access to maintenance scheduling information and to real-time instrument performance indicators. The built-in MicroActive for 3Flex software enables users to interactively assess evaluate isotherm data and minimize the time needed to get surface area and porosity results.

Analysis with 3Flex Surface Characterization Analyzer

It is a challenge to capture the filling of micropores at cryogenic temperatures because the filling of micropores start at very low pressures of around 10^-6 torr.

A single dose of gas like nitrogen may completely fill micropores like those contained in zeolites. Logarithmic isotherm overlay of 13X zeolite isotherms is shown in Figure 2.

Figure 2. Logarithmic isotherm overlay of 13X zeolite isotherms

A detailed isotherm leads to a detailed pore size distribution. The 3Flex also provides a reproducible isotherm collection from station to station. The simultaneous analysis of pore size distribution of three 13X zeolite samples is shown in Figure 3.

Figure 3. Pore size distribution of three 13X zeolite samples analyzed simultaneously

It is possible to generate and adjust calculations like the BET surface area transform plot as shown in Figure 4. Moreover it is possible to further refine the range of data used within the calculation windows.

Figure 4. Interactive selection of the BET surface area calculation range

New dosing options incorporated to the pressure table enable users to modify the equilibration interval time, volume dose increment, and pressure increment between data points, as illustrated in Figure 5.

Figure 5. The 3Flex pressure table allows data points to be taken in small increments of pressure, quantity dosed, or both

It is crucial to dose gas in small quantities during a micropore analysis as there is a direct relation between the measurement of pore size and the relative pressure at which the pore is filled. Hence, it is possible to determine smaller pore sizes when lower relative pressures are achieved.

The 3Flex can garner data at relative pressures down to 10^-9 with N₂ at 77 K with its 0.1-torr pressure transducer integrated with a high-vacuum system. Additional software options provide the capability to detect free space after analysis, thus eliminating the need to expose the sample to helium before analysis.

In certain cases, it is possible to retain helium by the presence of micropores and mask a part of the isotherm gleaned at very low relative pressure.

MicroActive for 3Flex software also enables users to superimpose a mercury porosimetry pore size distribution with a pore size distribution computed from gas adsorption isotherms, as shown in Figure 6. This new import function enables users to quickly observe macropore, mesopore, and micropore distributions in a single user-friendly application.

Figure 6. Overlay of BJH desorption and mercury intrusion pore size distributions for alumina pellets

3Flex Chemisorption Option

Chemical adsorption or chemisorptions as it is called, can offer most of the information required to study catalytic materials in the production and design phases as well as after being used for a specific period. Data about the active surface is obtained with the chemical adsorption isotherm.

Using the chemisorptions option, the 3Flex is designed to perform chemical adsorption analyses that allows the researcher to obtain information about the physical or chemical properties of catalysts, catalyst supports, and several other materials.

Features and Benefits

The key benefits of the chemisorption option are:

• VCR seals offer low outgas rates, better system cleanliness and base pressures. One can hence obtain precise low-pressure chemisorption isotherms and the ability to measure oxygen-sensitive materials
• Highly accurate, programmable gas control is offered by the high-precision mass flow controller
• Rapid and accurate ramp rates are offered to a desired temperature with very good repeatability and temperature control
• 12 gas inlets enable investigation of multiple probe gases improving efficiency and range of application
• Consistency and accuracy is maintained in monotonic isotherms by superior temperature control
• The design is such that transition from chemisorption to micropore physisorption is possible within seconds
• Sensitivity and accuracy is considerably improved for challenging analyses by a new high-temperature precision quartz cell.
• External detection such as with a mass spectrometer or a thermal conductivity detector for dynamic experiments such as TPR, TPD, or temperature-programmed surface reactions
• For chemical adsorption analysis, heated vapor can also be used as the adsorptive.
• Kalrez, Viton, or Buna O-rings provide maximum flexibility for chemical compatibility

Superior Hardware Versatility

With the chemisorptions capability, a 12-inlet gas manifold and vapor dosing are standard. Flow control during sample activation uses a mass flow controller (MFC) for precise and repeatable sample preparation. The MFC is included in the standard chemisorption hardware.

In situ Sample Preparation and Activation

In situ preparation and activation offer a completely automated technique that does not need user intervention and fully integrates activation and analysis into one simple-to-use application. Oxidation, reduction, purging and evacuation enable flexible pre-treatment options.

Sample Analysis Options

Sample analysis options include the following:

• Gas selection
• Free space measured at both ambient and analysis temperature
• Repeat isotherm to analyze reversible sorption
• Dosing options added to the pressure table give you the ability to change the pressure increment, volume dose increment, and equilibrium interval time between data points
• Dosing from gas inlets or vapor source

New Methods with a Common Interface

Unified Analysis Conditions for physical and chemical analyses helps in rapidly developing new methods with a common interface.

High-Resolution Isotherms

Manifold technology offers a very clean environment for chemisorptions and allows high-resolution isotherms to be developed for sorption on active surfaces. Reported data include crystallite size, active metal area, reversible and irreversible sorption, monolayer capacity and active metal dispersion.

Interactive MicroActive Software

MicroActive enables direct access and manipulation of chemical adsorption isotherm data. The intuitive graphical user interface permits rapid evaluation of data to determine both reversibly and irreversibly bound adsorbed gas quantities. The calculations include meta surface area, dispersion and crystallite size.

This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.

For more information on this source, please visit Micromeritics Instrument Corporation.