We develop catalytic tools (nanoparticles of precise size and shape) for structure sensitivity studies to gain insight into the origin of structure sensitivity and for active site determination and validation of the atomic leaching mechanism. The quantitative approach of applying crystal surface statistics to experimental data allows the understanding of real nanoparticle behavior and should help scientists to develop catalysts with surfaces approaching near-ideal model systems. Care is exercised to eliminate mass transfer limitations, which in some cases were shown to be responsible for the observed structure sensitivity. Similarly, selective removal of certain acid sites in zeolites may shed the light on their role in the main and side reactions.

Selected representative publications:

Effect of selective 4-membered ring dealumination on mordenite-catalyzed dimethyl ether carbonylation (Journal of Catalysis, 2017):

Palladium nanoparticle size effect in hydrodesulfurization of 4,6‐dimethyldibenzothiophene (4,6‐DMDBT) (ChemCatChem, 2016):

Nanoparticle shape effect study as an efficient tool to reveal the structure sensitivity of olefinic alcohol hydrogenation (Journal of Physical Chemistry C, 2010):

Size-and shape-controlled palladium nanoparticles in a fluorometric Tsuji–Trost reaction (Journal of Catalysis, 2011):

Our selected methods to control the structure of bimetallic nanoparticles allow for creating desirable core-shell or alloy materials and to distinguish reasons for observed synergism, which in some cases could be ascribed to one metal serving only as a dispersing agent for another. Careful attention is paid to the structure characterization and possibility of in situ surface rearrangement; there is an established collaboration with Canadian Light Source for ex situ and in situ characterization. Bimetallic synergism may exist also in ion-exchanged zeolites.

Selected representative publications:

Size-and structure-controlled mono-and bimetallic Ir–Pd nanoparticles in selective ring opening of indan (Journal of Catalysis, 2013):

Zinc hinders deactivation of copper-mordenite: dimethyl ether carbonylation (ACS Catalysis, 2016):

Iridium addition enhances hydrodesulfurization selectivity in 4,6-dimethyldibenzothiophene conversion on palladium (Applied Catalysis B: Environmental, 2016):

Structural evolution of bimetallic Pd-Ru catalysts in oxidative and reductive applications (Applied Catalysis A: General, 2015):

Platinum inhibits low‐temperature dry lean methane combustion through palladium reduction in Pd− Pt/Al2O3: An in situ X‐ray absorption study (ChemPhysChem, 2017):

In our catalyst development, we use colloidal chemistry techniques to synthesize mono- and bimetallic nanoparticles with a desired size, shape and structure, as well as porous nanoshells for their encapsulation. Such preparation techniques allow saving up to half of the scarce expensive noble metals without any loss in catalytic activity or replacing them with less rare metal combinations. Encapsulation in silica shells allows for high nanoparticle thermal stability and high metal loadings, leading to decreased reactor volumes. Significant attention is paid to the development of a suitable shell porosity for active site accessibility in the metal core.

Selected representative publications:

100° Temperature reduction of wet methane combustion: highly active Pd–Ni/Al2O3 catalyst versus Pd/NiAl2O4 (ACS Catalysis, 2015):

Nickel boosts ring‐opening activity of iridium (ChemCatChem, 2014):

Iridium-and platinum-free ring opening of indan (ACS Catalysis, 2013):

Natural gas vehicle fuel station (© 2008 Mario R. Duran):

Catalyst development for low-temperature methane combustion has received significant attention due to the growing market of alternative fuel vehicles, such as natural-gas vehicles (NGV) or biogas-powered vehicles. Natural gas has the highest energy/carbon ratio of any fossil fuel and produces the lowest emissions of not only CO₂ but also other pollutants (NO_x, SO_x, particulates, CO).

With demand rising, the market is not yet ready to meet the environmental and economic implications of the new technology. Methane itself has a global warming potential (GWP) that is 28-36 times higher than that of CO₂ over 100 years (data from the U.S. Environmental Protection Agency). As a result, in 2016 in Canada, methane emission control was put in place. Practically, the only way to eliminate these emissions is through the use of a catalytic converter, which constitutes the heart of an exhaust gas treatment system.

CH₄ is the most difficult of all hydrocarbons to burn, meaning that larger amounts of expensive noble metals must be used in the converters. Palladium catalysts are also subject to deactivation by water present in the engine exhaust and by sintering at high exhaust temperatures.

These indicate the immediate need for an efficient CH₄ combustion catalyst with the lowest possible noble metal loading and the smallest size and cost of the converter, which should at least be stable for the NGV lifetime. In our laboratories, we use a mindful combination of colloidal chemistry techniques to develop the required catalysts, which are tested under practically-relevant conditions.

A representative publication:

100° Temperature reduction of wet methane combustion: highly active Pd–Ni/Al2O3 catalyst versus Pd/NiAl2O4 (ACS Catalysis, 2015):

Forest affected by acid rain (image from wikipedia), which is formed from sulfur and nitrogen oxides:

Increasing global demand for ultra-low sulfur fuels has reinvigorated academic and industrial interest in developing active catalysts and energy-conscious technologies that are able to bring the S content down to 10 ppm. Sulfur reduction to such levels has to do primarily with the elimination of refractory sulfurous compounds such as dialkyl-dibenzothiophenes with alkyl groups adjacent to the sulfur atom, which makes the HDS process quite challenging. The reason is steric hindrance: alkyl groups prevent the perpendicular adsorption required for C-S bond hydrogenolysis on a catalyst surface. It is estimated that either pressure or reactor volumes must be tripled for efficient ultra-deep hydrodesulfurization (HDS). Powerful catalytic systems are urgently needed to meet the stringent environmental regulations along with the decreasing quality of the available raw materials.

In our approach, we develop nanocatalysts that are able to shift the HDS mechanism of the refractory sulfur compounds from a hydrogenation path, which requires high hydrogen pressure, to direct desulfurization at lower pressure. Specific attention is paid to reduce or even eliminate the need for platinum group metals in the catalysts for hydrotreatment.

A representative publication:

Iridium addition enhances hydrodesulfurization selectivity in 4,6-dimethyldibenzothiophene conversion on palladium (Applied Catalysis B: Environmental, 2016)