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Supported V2O5/Ce1–x Ti x O2 (3, 5, and 7 wt % V; x = 0, 0.1, 0.3, 0.5, 1) and bare supports have been tested in the selective catalytic reduction (SCR) of NO by NH3 at different gas hourly space velocities (GHSVs) and were comprehensively characterized using XRD, pseudo in situ XPS, and UV–vis DRS as well as EPR and DRIFTS in in situ and operando mode. The best V/Ce1–x Ti x O2 (x = 0.3, 0.5) catalysts showed almost 100% NO conversion and N2 selectivity already at 190 °C with a GHSV value of 70000 h–1, which belongs to the best performances observed so far in low-temperature NH3-SCR of NO. The corresponding bare supports still converted around 80% to N2 under the same conditions. On bare supports, SCR proceeds via a Langmuir–Hinshelwood mechanism comprising the reaction of adsorbed surface nitrates with adsorbed NH3. On V/Ce1–x Ti x O2, nitrate formation is not possible, and an Eley–Rideal mechanism is working in which gaseous NO reacts with adsorbed NH3 and NH4 +. Lewis and Brønsted acid sites, though adsorption of NH3, do not scale with the catalytic activity, which is governed rather by the redox ability of the materials. This is boosted in the supports by replacing Ce with the more redox active Ti and in catalysts by tight connection of vanadyl species via O bridges to the support surface forming −Ce–O–V­(O)–O–Ti– units in which the equilibrium valence state of V under reaction conditions is close to +5.

The impact of formaldehyde (HCHO, formed in vehicle exhaust gases by incomplete combustion of fuel) on the performance of a commercial V 2 O 5 -WO 3 /TiO 2 catalyst in NH 3 -SCR of NO x under dry conditions has been analyzed in detail by catalytic tests, in situ FTIR and transient studies using temporal analysis of products (TAP). HCHO reacts preferentially with NH 3 to a formamide (HCONH 2 ) surface intermediate. This deprives NH 3 partly from its desired role as a reducing agent in the SCR and diminishes NO conversion and N 2 selectivity. Between 250 and 400 °C, HCONH 2 decomposes by dehydration (major pathway) and decarbonylation (minor pathway) to liberate toxic HCN and CO, respectively. HCN was proven to be oxidized by lattice oxygen of the catalyst to CO 2 and NO, which enters the NH 3 -SCR reaction.

Cu single-atom catalysts (SACs) supported on CeO 2 −TiO 2 were prepared by a sol−gel method and tested for CO oxidation between 120 and 350 °C. Operando and in situ spectroscopic methods including diffuse reflectance infrared Fourier transform (DRIFT), electron paramagnetic resonance (EPR), and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with other basic characterizations were applied to identify active sites and to derive reliable structure−reactivity relationships. Rising the Cu content from 0.06 to 0.86 wt % resulted in a significant decrease of the Cu-mass normalized CO 2 formation rate from 690 to 310 μmol CO 2 •g Cu −1 •s −1 at 250 °C, which was attributed to the formation of the less active CuO x species. The catalysts showed high stability during time on stream for more than 1000 min with negligible agglomeration of Cu single sites. Spectroscopic results revealed that active sites are single Cu ions on the surface of highly dispersed ceria particles, shuttling between −Cu 2+ −O−Ce 4+ − and −Cu + −□−Ce 3+ − by supplying active oxygen for oxidation of CO to CO 2 . The highest concentrations of Cu single sites and O vacancies associated with Ce 3+ species correlated with the highest CO oxidation activity.

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As biodiesel production from triglyceride transesterification increases, a surplus amount of by-product glycerol is produced. The glycerol production per year in Europe has tripled within the last 10 years to 800-900 kt per year. This motivates the development of new processes for the conversion of glycerol into valuable chemicals, e.g., the transformation into acrolein. It is an attractive intermediate for acrylates, methionine, glutaraldehyde, etc. In the recent years, some researchers studied the dehydration of glycerol to acrolein over acidic bulk and supported catalysts, in particular with heteropolyacids (HPAs) as active compounds. HPAs attracted the attention due to their high Brønsted acidity and well known structures, however, they have some disadvantages such as low surface area, low thermal stability, and rapid coking leading to deactivation. To overcome these drawbacks, HPAs are often supported on oxidic carriers showing high surface areas. In addition, redox active metals are incorporated into HPAs and oxygen-containing feed is used to suppress coke formation. This review presents a summary on recent research on HPA based catalysts in the gas phase dehydration of glycerol to acrolein.

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