Swellable Organically Modified Silica (SOMS) as a Catalyst Scaffold for Catalytic Treatment of Water Contaminated with Trichloroethylene

Abstract

The properties of a swellable organically modified silica (SOMS) scaffold allowed us to synthesize "smart" catalysts with tunable accessibility of the active sites induced by organic swelling agents. Pd nanoparticles (NPs) deposited inside the swollen matrix of SOMS were shown to be selectively located on the interior surface, a surface which is only available through swelling. Techniques such as near ambient-pressure X-ray photoelectron spectroscopy (NAP−XPS) and cryogenic scanning electron microscopy (SEM) were employed to characterize Pd/ SOMS in its swollen as well as unswollen state because their conventional counterparts do not preserve the swollen state of Pd/SOMS during spectral acquisition. The results obtained depicted significant differences between the unswollen and swollen state of Pd/SOMS. The most important difference is that Pd NPs became accessible on the surface after exposure to an organic compound. This indicates that the accessibility of the active sites can be controlled by changing the reaction environment, hence allowing a tunable accessibility induced by organic swelling agents. The effects of the extent of swelling on the catalytic activity were investigated by performing catalytic activity experiments in the presence of an organic swelling agent. Hydrodechlorination (HDC) of trichloroethylene (TCE), an important method of catalytic water abatement, was chosen as a model reaction. The catalytic performance was found to be proportional to the concentration of the organic swelling agent, indicating that the accessibility of active sites is related to the concentration of organic compounds. While the unavoidable reaction product HCl inhibited the commonly used HDC catalyst 1%Pd/Al 2 O 3 , 1%Pd/SOMS was able to maintain its rate throughout the reaction under the same conditions, indicating its resistance to the inhibition. Overall, a silica-based catalyst with tunable accessibility of the active sites induced by changes in the reaction environment can have significant implications for heterogeneous catalysis.

Effect of High Temperature on Swellable Organically Modified Silica (SOMS) and Its Application for Preferential CO Oxidation in H2 Rich Environment

“…It can be clearly seen from all the samples that the uptake of acetone was favored over the uptake of water on the SOMS samples indicating their high affinity towards organic compounds as well as hydrophobicity. [32] The acetone uptake initially increases from SOMS to HSOMS-100 followed by an almost constant trend up to HSOMS-400. The textural properties (section 2.3.1) of these samples indicate that their surface areas do not differ significantly, however, their pore volumes increase with the temperature of treatment up to 400 o C. Despite these differences in pore volumes, the supports exhibit fairly similar acetoneuptake trends.…”

“…The equilibrium static vapor uptake of acetone and water were performed to assess the changes in the hydrophobicity of the SOMS supports after heat treatment. [29,32] Figure 4 shows the increase in mass of the support material after exposure to acetone or water vapors in a thermogravimetric analyzer. It can be clearly seen from all the samples that the uptake of acetone was favored over the uptake of water on the SOMS samples indicating their high affinity towards organic compounds as well as hydrophobicity.…”

“…[8] Also, it was recently reported that CO was found to have negligible interactions with the surface of SOMS while performing in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and hence, CO uptake due to adsorption on support itself was ruled out. [32] Celik et al found negligible uptake of CO on Pd supported on SOMS due to inaccessibility of active sites. [32] For a similar polymeric swellable material, Biffis et al also reported that, CO could not access the embedded Pd active sites.…”

“…[31] Previously, SOMS supported Pd catalysts have been used for the liquid and gas phase hydrodechlorination (HDC) of trichloroethylene (TCE). [32][33][34][35][36] Herein, the evolution of the properties of SOMS with increasing heat treatment under an inert atmosphere has been characterized and applied for the development of a water tolerant CoMn oxide catalyst. SOMS treated at 400 o C under helium was found to have the optimum textural properties for the same.…”

Pd/Fe nanoparticle integrated PMAA-PVDF membranes for chloro-organic remediation from synthetic and site groundwater

“…Specific to toxic chlorinated aliphatic/aromatic hydrocarbons, trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) are two of the contaminants of most concern [19][20][21][22]. Reductive dechlorination of TCE, PCBs and other toxic chlorinated hydrocarbons has been investigated using palladium/iron (Pd/Fe) bimetallic nanoparticles [23][24][25][26][27].…”