Application Note | Catalyst Surface Area
Surface Analysis of Carbon & Zeolite Catalysts Using 3D Profilometry
Roughness and Developed Surface Area of Porous Catalyst Pellets
Research & Experimental Testing
Andrea Herrmann
Visual Design & Editorial
Andrew Shore
Introduction
In order for a catalyst to be effective it must come into direct contact with the reactants, which is why increasing the available surface area of a catalyst directly increases the rate of reaction. In this study, the surfaces of the porous catalysts carbon and zeolite are characterized by their surface roughness and developed surface area.
Importance of 3D Non-Contact Profilometry for Surface Area Study
Unlike other techniques such as touch probes or interferometry, the 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any surface; sample sizes can vary widely due to open staging and there is no sample preparation needed. Nano through macro range is obtained during surface profile measurement with zero influence from sample reflectivity or absorption, with advanced ability to measure high surface angles and no software manipulation of results. It easily measures any material: transparent, opaque, specular, diffusive, polished, rough, etc. The technique of the non-contact profilometer provides an ideal, broad and user friendly capability to maximize surface studies, along with the benefits of combined 2D and 3D capability.
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Measurement Objective
In this application, the NANOVEA ST400 Profilometer is used to measure the surface of carbon and zeolite catalysts. The area measured was selected at random and assumed large enough to be extrapolated to a much larger surface. Surface roughness and developed area are used to characterize the available surface area.
NANOVEA ST400 Standard
Optical 3D Profilometer
Results
3D Surface
The 3D view and false color view show a randomly selected area on a carbon and a zeolite pellet. They provide users a straightforward tool to directly observe the morphology of the porous surface from different angles. It can be seen from the data tables that although the zeolite has a much higher average surface roughness of 21.5 µm, the carbon sample has a higher developed surface area of 6.44 mm².
| ISO 25178 parameter | Carbon | Zeolite |
|---|---|---|
| Sa (µm) | 5.158 | 21.50 |
| Sq (µm) | 6.831 | 27.67 |
| Sp (µm) | 33.13 | 99.34 |
| Sv (µm) | 82.86 | 89.73 |
| Sz (µm) | 116.0 | 189.1 |
| Ssk | −1.26 | 0.03892 |
| Sku | 7.891 | 3.148 |
| Spar, projected area (mm²) | 3.999 | 3.997 |
| Sdar, developed area (mm²) | 6.444 | 5.651 |
Table 1: Surface parameters of the carbon and zeolite pellets (from Figs. 2 and 3).
Conclusion
In this application, we have shown how the NANOVEA 3D Non-Contact Profilometer can precisely characterize the porous surfaces of carbon and zeolite catalyst pellets. The data shows an average surface roughness of 5.158 µm and 21.50 µm for the carbon and zeolite, respectively. The developed surface area was found to be 6.444 mm² for the carbon and 5.651 mm² for the zeolite. That is an increase over the projected surface area of 61.1% for the carbon and 41.4% for the zeolite. The data shown here represents only a portion of the calculations available in the analysis software.
Frequently Asked Questions About Catalyst Surface Measurement
Why does catalyst surface area matter?
A catalyst must contact the reactants directly, so increasing its available surface area directly increases the rate of reaction.
What is developed surface area?
The true 3D area of the measured surface (Sdar), compared with its flat projected area (Spar); the ratio shows how much extra surface the texture provides.
Which pellet was rougher?
The zeolite, with an average roughness Sa of 21.50 µm against 5.158 µm for the carbon.
Which pellet had more surface area?
The carbon: a developed area of 6.444 mm² over 3.999 mm² projected, a 61.1% increase, against 5.651 mm² over 3.997 mm² (41.4%) for the zeolite.
Can a small scan represent a whole pellet?
The measured area was selected at random and assumed large enough to be extrapolated to a much larger surface.
Does the porous surface need preparation?
No. Axial chromatism measures without contact or sample preparation, with no influence from reflectivity or absorption.
