The project involves the development of catalysts for the reduction of inorganic ions in water and wastewater and for the oxidation of volatile organic compounds (VOCs) and carbon monoxide in air and gaseous streams.

Catalytic Reduction of Inorganic Ions

The increasing concentration of chemicals in groundwater and the increasingly demanding quality standards for drinking water, generate the urgent need for improved technologies and processes for water remediation, in order to protect the environment and human health.

Catalytic reduction has been suggested as a promising technology to remove anions from water sources, without the formation of solid or liquid wastes, or possible bacterial contaminations. In this topic, the catalytic reduction of ions (such as nitrate, bromate and perchlorate) with hydrogen is studied in a systematic way, focusing on the use of carbon-supported metal catalysts.

Pd-Cu supported on basic carbon materials was found to be the most active and selective catalyst. This catalytic system performed equally well in the reduction of bromate ions.

TEM image of Pd-Cu supported on carbon nanotubes

Nitrate conversion in the presence of Pd-Cu catalysts supported on different materials

Nitrate reduction in the presence of Pd-Cu catalysts supported on different carbon materials

Turn-over frequencies (TOF) for bromate reduction using catalysts supported on TiO2 and MWCNT

Catalytic Oxidation of VOCs

Volatile organic compounds (VOCs) are emitted from a wide range of industrial processes and transportation activities and have a major contributor to air pollution because of their toxic and malodorous nature and their involvement in ozone depletion and smog formation. Thermal oxidation of VOCs needs to operate in a range of temperatures between 700 and 1000ºC, which leads to NOx production from the N₂ present in air. In the case of catalytic oxidation, the operation temperature decreases to around 250–500ºC, therefore, NO_x production is much lower, and less energy is needed to preheat the stream. Ideally the products obtained are CO₂ and water. The performance of this process critically depends on the type of catalyst, which is a function of the gaseous effluent to be treated (composition, flow-rate, presence of poisons or/and inhibitors in the gas stream, and inlet temperature constraints).

Cryptomelane-manganese oxides based catalysts, supported gold nanoparticles, exotemplated and mixed metal oxides, and monoliths coated with manganese oxides, have been successfully used as catalysts.

Bench-scale testing rig for VOC oxidation catalysts

SEM micrograph of a cryptomelane manganese oxide catalyst

Light-off curves for ethyl acetate oxidation on various types of manganese oxide catalysts

Pilot-plant VOC oxidation reactor

Catalytic Oxidation of CO

Gold catalysts have been successfully used for CO oxidation, as well as in the water-gas shift reaction (CO + H₂O → CO₂ + H₂). Moreover, gold is more selective than Pt and other PGMs for the oxidation of CO in the presence of H₂ (PROX), is nearly insensitive to CO₂, and its activity is enhanced by water. Thus, Au catalysts are good candidates for H₂ production and purification. We have been focusing our attention on the catalyst preparation methods in order to achieve high activity at low temperatures.

Effect of gold loading by different methods on the CO conversion with Au/ZnO

TEM (left) and HRTEM (right) images of Au nanoparticles deposited by US on ZnO

Light-off curves of K-OMS-2 and Ce–K-OMS-2 with and without Au for CO oxidation

SEM (left) and HRTEM (right) images of Au on cryptomelane (K-OMS-2)