Localized Chemistry Department of Chemistry, University of Waterloo

Research

Solid-State Reactivity & Catalysis

Studying reactions in and on solid materials to learn how to guide phase transformations and catalyst performance.

aTwo ways to make the intermetalliciron reaches the melt from one side, or from bothunmodifiedsteelAl–Si coatingFe-coatedsteelAl–Si coatingFe sourceOne front becomes two, and they close on each other.bThe colours are assignmentsmeasured reference spectra, one per phaseτ₂τ₅τ₆θAl₁₃Fe₄ηAl₅Fe₂100200300400500Raman shift (cm⁻¹)cWhere each phase sits, after 2 minRaman speciation maps, steel at the back of every strip600 °Cunmodified6 µmFe-coated23 µm620 °Cunmodified6 µmFe-coated26 µm640 °Cunmodified5 µmFe-coated25 µm800 °Cunmodified5 µmFe-coated24 µmintermetallic22MnB5 steelτ₆τ₅θηintermetallic, increasing Fe →unreacted Al–SiFe sourceMaps are drawn from the per-pixel Raman phase assignments; each is scaled to the same frame.Zhang et al., ACS Appl. Mater. Interfaces 2025

Supplying iron at the outer surface speeds up the coating’s transformation. During industrial hot stamping, the Al–Si coating on 22MnB5 steel converts to Fe–Al intermetallics, and the rate depends on how quickly iron can dissolve out of the steel into the melt. (a) When iron is available only from the steel below, the intermetallic grows as a single front. Adding an iron source at the outer surface starts a second front, and the two fronts move toward each other. (b) Each colour in the maps corresponds to a measured reference spectrum. The intermetallics are shown as shades of one hue, ordered by iron content. (c) Raman speciation maps across the coating after the same two-minute hold. The unmodified coating forms a 5–6 µm intermetallic band at the steel interface, and the rest of the coating remains unreacted at every temperature. The modified coating has converted 23–26 µm, growing inward from both faces. Maps are drawn from the per-pixel phase assignments at 1 µm per pixel. Data from Zhang et al., ACS Appl. Mater. Interfaces 2025.

Solid-state reactions and heterogeneous catalysis have a lot in common. In a solid-state reaction, the solid itself is transformed. In catalysis, the solid transforms other molecules and is regenerated. Both depend on defects and interfaces, and both can be limited by reaction kinetics or diffusion. In either case, the most useful information usually comes from measuring structure at different stages of the reaction.

We make those measurements as samples are heated, dosed with reactants, or run under realistic process conditions.

What we work on

  • Catalysis for chemical manufacturing. Solid-state catalysts for industrial reactions in fixed-bed flow reactors, catalyst-coated ceramics for scale-up, and the reduction behaviour of supported metals.
  • Catalyst fabrication. Designing pre-catalysts and fabrication routes so that the finished catalyst contains as many of the structural features responsible for activity as possible.
  • Industrial phase transformations. Conversion of aluminum-silicide coatings to intermetallic phases during hot stamping of automotive steel, tracked with in-situ Raman spectroscopy.
  • Defect engineering in layered materials. Detecting, quantifying, adding, and removing defects in MoS2 and related materials, the feedback loops that drive their degradation, and the fabrication methods used to prepare them: exfoliation, Langmuir assembly, and atomic layer deposition.
  • Reaction mechanisms in oxides. Spontaneous carbonation of layered cuprates, and the pathways connecting iron oxyhydroxide phases.

Why it matters

Solving a materials problem in a targeted way requires knowing the mechanism. The mechanism shows where a process can be changed to fix the problem. In the coating work shown above, finding that the transformation rate depends on iron supply pointed to adding a second iron source at the outer surface.