Effect of initial support particle size of MnO x /TiO2 catalysts in the selective catalytic reduction of NO with NH3

Direct dimethyl carbonate synthesis from CO2 and methanol over a flower-like CeO2 catalyst with 2-cyanopyridine as a dehydrating agent in continuous packed-bed reactor

A flower-like CeO2 catalyst was successfully synthesized using an acrylamide graft copolymerized on glucose under hydrothermal conditions and used for the direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH in a packed-bed reactor with 2-cyanopyridine as a dehydrating agent. The synthesized flower-like CeO2 exhibited both basicity and acidity properties with values of 300 μmol g-1 and 80 μmol g-1, respectively, according to CO2-TPD and NH3-TPD results. The effect of reaction parameters such as reaction temperature, feed ratio, catalyst quantity, and operating pressure on the DMC production over the flower-like CeO2 catalyst was investigated. The optimum conditions were found to be a temperature of 120 °C, catalyst weight of 1.0 g, CH3OH : CO2 ratio of 1 : 1, and pressure of 30 bar, which provided the highest CH3OH conversion, DMC selectivity, and DMC yield of 86.6%, 99.3%, and 86.0%, respectively. Furthermore, no changes were observed in the structure, morphology, and particle size of the flower-like CeO2 catalyst after the DMC synthesis reaction, indicating that the synthesized catalyst was resistant to the reaction test under such optimum reaction conditions.

Recent progress of low-temperature selective catalytic reduction of NOx with NH3 over manganese oxide-based catalysts

Selective catalytic reduction with NH3 (NH3−SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NOx). Although the conventional manganese oxide-based catalyst had gradually become a kind...

Promotional mechanism of enhanced denitration activity with Cu modification in a Ce/TiO2-ZrO2 catalyst for a low temperature NH3-SCR system

This study aims to investigate the enhanced low temperature denitration activity and promotional mechanism of a cerium-based catalyst through copper modification. In this paper, copper and cerium oxides were supported on TiO2-ZrO2 by an impregnation method, their catalytic activity tests of selective catalytic reduction (SCR) of NO with NH3 were carried out and their physicochemical properties were characterized. The CuCe/TiO2-ZrO2 catalyst shows obviously enhanced NH3-SCR activity at low temperature (<300 °C), which is associated with the well dispersed active ingredients and the synergistic effect between copper and cerium species (Cu2+ + Ce3+ ↔ Cu+ + Ce4+), and the increased ratios of surface chemisorbed oxygen and Cu+/Cu2+ lead to the enhanced low-temperature SCR activity. The denitration reaction mechanism over the CuCe/TiO2-ZrO2 catalyst was investigated by in situ DRIFTS and DFT studies. Results illustrate that the NH3 is inclined to adsorb on the Cu acidic sites (Lewis acid sites), and the NH2 and NH2NO species are the key intermediates in the low-temperature NH3-SCR process, which can explain the promotional effect of Cu modification on denitration activity of Ce/TiO2-ZrO2 at the molecular level. Finally, we have reasonably concluded a NH3-SCR catalytic cycle involving the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism, and the former mechanism dominates in the NH3-SCR reaction.

MOF-74-M (M = Mn, Co, Ni, Zn, MnCo, MnNi, and MnZn) for Low-Temperature NH3-SCR and In Situ DRIFTS Study Reaction Mechanism

Monometallic and bimetallic MOF-74-M (M = Mn, Co, Ni, Zn, MnCo, MnNi, and MnZn) catalysts were prepared by the solvothermal method for NH₃-SCR. XRD, BET, SEM, and EDS-mapping tests indicate the successful synthesis of the MOF-74-M catalyst with uniform distribution of metal elements and large specific surface area, and the morphology is almost hexagonal. Adding Mn element to a single-metal catalyst can enhance activity, which is mainly because of the existence of various valence states of Mn so that it has excellent redox properties; the catalytic activity of water and sulfur resistance tests showed that the catalytic activity of MOF-74-M increases after adding a proper amount of SO₂, mainly because of the increase in acidic sites. In situ DRIFTS results indicate that the low-temperature range of MOF-74-MnCo and MOF-74-Mn is dominated by the E-R mechanism and the high-temperature range is dominated by the L-H mechanism. The entire temperature range of MOF-74-Zn is dominated by the L-H mechanism.