Ir-Catalysed Nitrous Oxide (N2O) Decomposition:Effect of Ir Particle Size and Metal–Support Interactions

The effect of the morphology of Ir particles supported on γ-Al2O3, 8 mol%Y2O3-stabilized ZrO2 (YSZ), 10 mol%Gd2O3-doped CeO2 (GDC) and 80 wt%Al2O3–10 wt%CeO2–10 wt%ZrO2 (ACZ) on their stability on oxidative conditions, the associated metal–support interactions and activity for catalytic decomposition of N2O has been studied. Supports with intermediate or high oxygen ion lability (GDC and ACZ) effectively stabilized Ir nanoparticles against sintering, in striking contrast to supports offering negligible or low oxygen ion lability (γ-Al2O3 and YSZ). Turnover frequency studies using size-controlled Ir particles showed strong structure sensitivity, de-N2O catalysis being favoured on large catalyst particles. Although metallic Ir showed some de-N2O activity, IrO2 was more active, possibly present as a superficial overlayer on the iridium particles under reaction conditions. Support-induced turnover rate modifications, resulted from an effective double layer [Oδ−–δ+](Ir) on the surface of iridium nanoparticles, via O2− backspillover from the support, were significant in the case of GDC and ACZ

Nitrous oxide decomposition in a real nitric acid plant gas stream with a RhOx/Ce0.9Pr0.1O2/alumina catalyst

Background: N2O is a powerful greenhouse gas emitted in nitric acid plants, and emission control technologies are required. Results: A 0.25%Rh/50%Ce0.9Pr0.1O2/γ-Al2O3 catalyst has been prepared and tested for N2O decomposition in a real nitric acid plant gas stream. The catalyst is active enough to achieve 100% N2O removal, maintaining a constant catalytic activity after 40 h operation without deactivating. Characterization of the fresh and used catalyst, using different techniques, revealed no changes during the N2O decomposition experiments: (i) XRD and Raman spectroscopy show the fluorite structure of the Ce–Pr mixed oxide before and after the catalytic tests, (ii) the crystal size of the Ce–Pr mixed oxide particles and the BET surface area of the catalyst is maintained, evidencing no sintering of ceria particles, (iii) H2-TPR indicates that the reducibility of the catalyst is similar before and after the catalytic tests, revealing chemical stability, and (iv) TEM and XPS analysis indicated the high stability of the rhodium particle size and oxidation state. Conclusion: An active and stable catalyst with formulation 0.25%Rh/50%Ce0.9Pr0.1O2/γ-Al2O3 has been prepared and successfully tested for N2O decomposition in a real nitric acid plant gas stream.The authors acknowledge the financial support of Generalitat Valenciana (Project Prometeo 2009/047) and EU (FEDER), and S. Parres the University of Alicante-CAM-Unión FENOSA for her thesis grant

Operando micro-spectroscopy on ZSM-5 containing extrudates during the oligomerization of 1-hexene

The influence of the binder material in an industrial-type catalyst material is often neglected, although the addition of a binder can cause a significant change in the performance of the catalyst. It is difficult to visualize the effects of the different components in these multi-complex materials, and therefore, high spatiotemporal resolution techniques need to be employed. In this work, two complementary micro-spectroscopic techniques; operando UV-vis diffuse reflectance micro-spectroscopy (coupled to on-line mass spectrometry), and in situ confocal fluorescence microscopy were used to investigate the 1-hexene oligomerization reaction. The reaction was performed on both Al2O3- and SiO2-bound ZSM-5-containing extrudates at 250 °C and 300 °C. By employing operando UV-vis micro-spectroscopy, coupled with on-line mass spectrometry, Al2O3-bound catalysts were found to form larger reaction products, as well as more and larger hydrocarbon deposits, compared to the SiO2-bound catalysts. Furthermore, the extrudate containing Al2O3 deactivated slower than the extrudate containing SiO2 binder. Time-resolved chemical maps of the location of the reaction products were visualized using in situ confocal fluorescence microscopy. The maps show that, after reaction, the zeolite crystals contain different coke species than the Al2O3 binder

Chemical Imaging of the Binder-Dependent Coke Formation in Zeolite-Based Catalyst Bodies During the Transalkylation of Aromatics

The choice of binder material, added to a zeolite‐based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4‐trimethylbenzene (1,2,4‐TMB). Using in situ UV‐vis micro‐spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al2O3‐bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3‐binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4‐TMB in the SiO2‐bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals

Chemical Imaging of the Binder-Dependent Coke Formation in Zeolite-Based Catalyst Bodies During the Transalkylation of Aromatics

The choice of binder material, added to a zeolite‐based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4‐trimethylbenzene (1,2,4‐TMB). Using in situ UV‐vis micro‐spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al2O3‐bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3‐binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4‐TMB in the SiO2‐bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals