Page 128 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Application of heterogeneous acid catalyst derived from biomass for biodiesel process 99

4.5 Catalyst characterization techniques

The primary objective of catalyst characterization is to define the correlation of
their physical, chemical, thermal, and mechanical properties of catalysts, along with
its deactivation, which is essential to study about the optimization of the process
and to determine the selection of feedstock. The other major goal of the characteri-
zation is to monitor the changes involved in chemical and physical properties of
catalysts during preparation, activation, reaction, and regeneration stages for better
understanding and quality.
The biomass-based catalysts prepared through different methods are character-
ized by the following techniques. The topographical, morphological, and crystallo-
graphic structures of the catalyst are determined by SEM that has an operating
range between 1 and 10 nm. For a better understanding of the morphology of the
solid structure, transmission electron microscopy is also employed which has a res-
olution power up to 0.2 nm (Egerton, 2005). SEM is usually coupled with Energy
Dispersive X-ray (EDX) to identify the atomic mass of each element present in the
sample through which possible chemical species attached to it can be predicted.
Nonetheless, the resolution of EDX analysis is not adequate to find out the exact
locations of the elements in bulk (Dehkhoda et al., 2010).
Bohem titrometry is used for determining total acid density of functionalized cat-
alyst (Boehm, 1966; Lazzarini et al., 2017). This method is easy, reliable, and cost
effective. It gives a summation of all acidic functional groups present in the sample
such as sulfonic, carboxylic, and phenolic. However, the individual acid group
responsible for both esterification and transesterification cannot be identified.
Nitrogen adsorption and desorption isotherms are used for investigating the sur-
face area by BET method and pore size distribution by Barrett Joyner Halenda
method. Attention should be provided during the calculation of BET surface area
because it will be slightly lesser than the actual surface area due to the enhanced
interactions of the gas inside the pores (Brunauer et al., 1938).
XRD is used to analyze the crystal structure. Similarly, surface concentrations of
the various species can be estimated from the peak size bound to the catalyst using
X-ray Photon Spectroscopy (XPS) (Boehm, 2002). XPS is a fine tool to probe both
Lewis and Bronsted sites.
Thermal stability is a very important characteristic used in extreme operational
condition of the catalyst. It is determined using Thermal Gravimetric Analysis
(TGA) that also finds its importance to give some reliable data regarding moisture
content, volatile materials, and the minimum temperature required for the decompo-
sition of organic and inorganic contents. The determination of carbonization tem-
perature for biomass is also done using this method. The limitation of TGA is that
it is only limited to change in mass with respect to temperature.
Fourier-transform infrared spectroscopy is utilized for analyzing the presence of
functional group on the biomass catalyst surface. In this spectral analysis, distinc-
tive peaks related to C C, SO 3 H, and C H stretching indicate the polycyclic
aromatic carbon sheet, attachment of sulfonic group, and hetero aromatic