Selective Catalytic Reduction with Hydrogen for Exhaust gas after-treatment of Hydrogen Combustion Engines

Abstract

In this work, two palladium-based catalysts with either ZSM-5 or Zeolite Y as support material are tested for their performance in selective catalytic reduction of NOx with hydrogen (H2-SCR). The ligh-toff measurements in synthetic exhaust gas mixtures typical for hydrogen combustion engines are supplemented by detailed catalyst characterization comprising N2 physisorption, X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR) and ammonia temperature programmed desorption (NH3-TPD). Introducing 10% or 20% TiO2 into the catalyst formulations reduced the surface area and the number of acidic sites for both catalysts, however, more severely for the Zeolite Y-supported catalysts. The higher reducibility of the Pd particles that was uncovered by H2-TPR resulted in an improved catalytic performance during the light-off measurements and substantially boosted NO conversion. Upon exposition to humid exhaust gas, the ZSM-5-supported catalysts showed a significant drop in performance, whereas the Zeolite Y-supported catalyst kept the high levels of conversion while shifting the selectivity from N2O more toward NH3 and N2. The 1%Pd/20%TiO2/HY catalyst subject to this work outperforms one of the most active and selective benchmark catalyst formulations, 1%Pd/5%V2O5/20%TiO2-Al2O3, making Zeolite Y a promising support material for H2-SCR catalyst formulations that allow efficient and selective NOx-removal from exhaust gases originating from hydrogen-fueled engines.

Pt-based catalysts for NOx reduction from H2 combustion engines

“…14a) thus it is likely that the band at 1454 cm −1 is an overlap between ammonia and water on the surface. NH 3 has been reported as a by-product of H 2 -SCR in many publications, 54,83 however the activity test in our study (section: Reaction process) did not reveal the presence of ammonia. Instead, through DRIFTS the presence of ammonium ions is shown, suggesting that the Pt/SSZ-13 could store NH 4 + .…”

MOx@VOx‐Pd‐type Nanorods and Nanotubes as Catalysts for Selective Reduction of NO

“…The monolithic reference catalyst, however, outperforms the VO x ‐Pd nanotubes with respect to NH 3 emission. The reference catalyst's lower tendency to form NH 3 is likely due to the presence of TiO 2 , whose addition to the H 2 ‐SCR catalyst formulation was recently reported to be a suiTable Strategy to minimize NH 3 formation [9b] …”

“…First, the surface area of 387 m 2 /g that was determined for the l‐TiO 2 @VO x nanotubes exceeds the surface area of the ZnO@VO x nanorods (27 m 2 /g) and VO x nanotubes (25 m 2 /g) by far, hereby providing a large surface for the adsorption of reactive species, which ultimately promotes noble metal to metal‐oxide support interactions that were found to trigger the H 2 ‐SCR reaction [8] . Second, the addition of 10 to 20 wt‐% of TiO 2 to zeolitic support materials with a high surface area was recently reported as highly beneficial for the activity and product selectivity of Pd‐based H 2 ‐SCR catalysts, presumably due to an increased reducibility of active Pd sites and an enhanced activation of reactants, which involves both the noble metal as well as the support material [9b] . Hence, we can assume that TiO 2 promotes the reduction of NO x with H 2 also for thel‐TiO 2 @VO x nanotube catalyst.…”

Elucidating the role of the state of Pd in the H2-SCR of NOx by operando XANES and DRIFTS

“…15 There are several primary groups of catalyst supports that have been studied in H 2 -SCR: (1) TiO 2 , [28][29][30][31][32] often combined with V 2 O 5 , 26,27,33,34 (2) WO 3 /ZrO 2 , [35][36][37][38] and (3) MgO-CeO 2 , [19][20][21] and (4) zeolites, alone or in combination with other supports. [39][40][41][42][43] H 2 -SCR catalysts with low noble metal loadings (<1 wt%) of Pt or Pd on WO 3 /ZrO 2 or MgO-CeO 2 have shown wide temperature ranges (100 to 400 °C) of NO x conversion with high (>80%) selectivity for N 2 . However, they have not been studied as extensively as catalysts supported on TiO 2 .…”