Me-ZSM-5 monolith foams for the NH 3 -SCR of NO

Cu/ZSM5-Geopolymer 3D-Printed Monoliths for the NH3-SCR of NOx

Geopolymer-based monoliths manufactured by direct ink writing, containing up to 60% by weight of presynthesized ZSM5 with low Si/Al ratio, were investigated as structured catalysts for the NH3-SCR of NOx. Copper was introduced as the active metal by ion exchange after a preliminary acid treatment of the monoliths. Monolithic catalysts were characterized by morphological (XRD and SEM), textural (BET and pore size distribution), mechanical (compressive strength), chemical (ICP–MS), redox (H2-TPR) and surface (NH3-TPD) analyses, showing the preservation of Cu-exchanged zeolite features in the composite monoliths. NH3-SCR tests, carried out on both monolithic and powdered samples in the temperature range 70–550 °C, confirmed that composite monoliths provide a very good activity and a high selectivity to N2 over the whole range of temperatures explored due to the hierarchical structure of the materials, in addition to a good mechanical resistance—mostly related to the geopolymer matrix.

Highly dispersed MnOx–FeOx supported by silicalite-1 for the selective catalytic reduction of NOx with NH3 at low temperatures

MnO_x–FeO_x-Loaded silicalite-1 catalysts exhibit high NO_x conversion at low temperatures.

Catalytic Performance of Toluene Combustion over Pt Nanoparticles Supported on Pore-Modified Macro-Meso-Microporous Zeolite Foam

Herein, to investigate the pore effect on toluene catalytic oxidation activity, novel supports for Pt nanoparticles-ZSM-5 foam (ZF) fabricated using polyurethane foam (PUF) templates and pore-modified ZSM-5 foam (ZF-D) treated by acid etching, comparing with conventional ZSM-5 and pore-modified ZSM-5 (ZSM-5-D), were successfully synthesized. Pt nanoparticles were loaded on series ZSM-5 supports by the impregnation method. The Pt loaded on ZF-D (Pt/ZF-D) showed the highest activity of toluene catalytic combustion (i.e., T₉₀ = 158 °C), with extraordinary stability and an anti-coking ability. Based on various catalysts characterizations, the unique macropores of ZF facilitated the process of acid etching as compared to conventional ZSM-5. The mesopores volume of ZF-D significantly increased due to acid etching, which enlarged toluene adsorption capacity and led to a better Pt distribution since some Pt nanoparticles were immobilized into some mesopores. Specifically, the microporous distribution was centered in the range of 0.7-0.8 nm close to the molecular diameter of toluene (ca. 0.67 nm), which was key to the increasing toluene diffusion rate due to pore levitation effect of catalysts and accessibility of metal. Furthermore, the reducibility of Pt nanoparticles was improved on Pt/ZF-D, which enhanced the activity of toluene catalytic oxidation.

A Case Study for the Deactivation and Regeneration of a V2O5-WO3/TiO2 Catalyst in a Tail-End SCR Unit of a Municipal Waste Incineration Plant

In this work, we set out to investigate the deactivation of a commercial V2O5-WO3/TiO2 monolith catalyst that operated for a total of 18,000 h in a selective catalytic reduction unit treating the exhaust gases of a municipal waste incinerator in a tail end configuration. Extensive physical and chemical characterization analyses were performed comparing results for fresh and aged catalyst samples. The nature of poisoning species was determined with regards to their impact on the DeNOx catalytic activity which was experimentally evaluated through catalytic tests in the temperature range 90–500 °C at a gas hourly space velocity of 100,000 h−1 (NO = NH3 = 400 ppmv, 6% O2). Two simple regeneration strategies were also investigated: thermal treatment under static air at 400–450 °C and water washing at room temperature. The effectiveness of each treatment was determined on the basis of its ability to remove specific poisoning compounds and to restore the original performance of the virgin catalyst.

Leaf-like Co-ZIF-L derivatives embedded on Co2AlO4/Ni foam from hydrotalcites as monolithic catalysts for toluene abatement

Herein, a series of distinctively monolithic catalysts were first synthesized by decorating leaf-like Co-ZIF-L derivatives on Co₂AlO₄ coral-like microspheres from CoAl layered double hydroxides (LDHs), which were coated on three-dimensional porous Ni foam. As a proof of concept application, toluene was chosen as a probe molecule to evaluate their catalytic performances over the as-synthesized catalysts. As a result, the L-12 sample derived from Co₂AlO₄@Co-Co LDHs displayed an excellent catalytic performance, cycling stability and long-term stability for toluene oxidation (T₉₉ = 272 °C, 33 °C lower than that of Co₂AlO₄ sample), where leaf-like Co-ZIF-L served as a sacrificial template to synthesize Co-Co LDHs. The improved catalytic performance was attributed to its distinctive structure, in which leaf-like Co-ZIF-L derivatives on Co₂AlO₄ resulted in its higher specific surface area, lower-temperature reducibility, rich surface oxygen vacancy and high valence Co³⁺ species. This work thus demonstrates a feasible strategy for the design and fabrication of hybrid LDHs/ZIFs-derived composite architectures, which is expected to construct other novel monolithic catalysts with hierarchical structures for other potential applications.

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH3-SCR Catalysts

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na+ on catalysts and results in the loss of both Brönsted acid sites and Cu2+ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO2/NaSiO3 and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu2+ ions finally transformed into CuxO, CuO, and CuAlOx species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu2+ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu2+ ions, as well as copper oxide species (CuxO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions’ effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications.