Pyroelectrically Activated Lean-Gas Catalysis: Pseudocapacitor-Inspired NOx/CO Capture with Surrogate Noble Metal Lean NOx Traps

Introduction. Diesel cold-start engines still account for the majority of regulated NOx and CO emissions because conventional lean NOx traps (LNTs) do not reach the light-off state until > 250 °C and rely on costly Pt/Pd/Rh. We report a multilayer LNT stack that replaces noble metals with a low-cost Surrogate Noble Metal (SNM) nitride and embeds a pyroelectric sheet that harvests the exhaust’s natural 80 → 180 °C ramp to deliver a self-generated 0.3–0.4 V surface pulse. This “pseudocapacitor” kick-starts electropromotion, enabling simultaneous NOx and CO conversion from < 200 °C through full-load conditions.

Methods. A 15 nm SNM nitride was high-power-impulse-sputtered onto 8 mol % YSZ monolith channels and over-coated with a 5 µm BaO/Ce₀.₇Zr₀.₃O₂ storage layer. A 200 µm Ca-doped YMnO₃ sheet, hot-pressed between the monolith and a stainless-steel heat spreader, generated the pyroelectric voltage during temperature transients. Catalytic performance was assessed under alternating lean (12 % O₂) and rich (1 % CO) feeds in a transient flow reactor, while operando X-ray absorption (SNM K-edge) and DRIFTS monitored metal redox and nitrate dynamics over 40 lean/rich cycles.

Results. The pyroelectric pulse reduced SNM^δ+ to metallic SNM within 15 s, drove K⁺ migration to the SNM/oxide interface, and doubled CO adsorption entropy. Consequently, ≥ 90 % NOx and 75 % CO conversion were achieved at 180 °C—22 % higher than a Pt-Ba/Al₂O₃ benchmark while using 60 % less precious metal overall. Durability tests (40 cycles, 650 °C regenerations) showed only 8 % storage capacity loss and < 3 nm particle growth, establishing the first all-temperature dual-redox LNT that is self-powered and cost-efficient.