(239g) Synthesis and Characterization of Biochar-Based Carbon Supported Metal Nanoparticles

Synthesis and characterization of
biochar-based carbon supported metal nanoparticles

Sai Teja Neeli and Hema Ramsurn

Russell School of Chemical Engineering,
University of Tulsa, Tulsa, OK 74104

Biochar is a carbon-rich solid
formed after biomass has been carbonized. It is also a residue from a number of
thermochemical conversion processes whereby biomass is converted to bio-oil
and/or syngas. Therefore, this material is environmental-friendly and
carbon-neutral. Traditionally, biochar has been used as soil amendments for the
healthy growth of plants due to its retention capability of nutrients. This
investigation aims to use biochar in a different manner: as a support for metal
catalysts to promote green chemistry and engineering. The biochar used in this
study is obtained from hydrothermal carbonization of model compounds of biomass
namely lignin, cellulose and hemicellulose. This means that high pressure and
temperature water is used as a benign solvent to depolymerize the model
compounds to biochar. The biochar so produced is chemically activated with 0.1
M HNO₃ solution resulting in activated carbon with defined micropore
size distribution, high micropore volumes and large specific surface areas.
Metal precursors (like iron nitrate) are then added to the biochar and dried in
a convection oven at 110 ^o C for one week to obtain metal (iron)
impregnated biochar. The dried mixture is thermally-treated in a quartz tubular
reactor at 1000 ^o C for one hour in a nitrogen flow of 500 ml/min. These
synthesized biochar based metal catalysts will then be characterized using a
number of techniques including scanning electron microscope (SEM), x-ray powder
diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES)
and Brunauer-Emmett-Teller (BET) surface area
analyzer. Other metal catalysts such as platinum, gold and nickel can also be impregnated
on the biochar in the same manner. It is expected to observe distinct XRD
patterns corresponding to graphite for the thermally treated metal-impregnated
biochar, due to the conversion of the carbonaceous materials to graphite. SEM
images will help not only in sizing the metal nanospheres
(about 20 -60 nm) but also in determining how the metal is supported: half
embedded or completely enclosed in the porous char matrix. Based on the
characterization results, these metal-impregnated biochar catalyst could be
tested for a number of reactions. These supports can withstand high
temperatures and can even be used for gasification reactions and upgrading
bio-oil during hydrogenation reactions. There is also the possibility of using
bifunctional metal/acid catalysts on the biochar nanoparticles for dehydration
and hydrogenation reactions and for aqueous phase processing to produce
selectively targeted alkanes from glucose. The ultimate goal is to use these green
catalysts to upgrade the oxygenated biofuels by removing the oxygen through
various mechanisms and hence increasing the quality and heating value of the
desired product.