Tunable preparation of highly dispersed Ni x Mn-LDO catalysts derived from Ni x Mn-LDHs precursors and application in low-temperature NH3-SCR reactions

Unraveling Excellent Performance in NH3-SCR over Cr-Doped NiMn-LDO Catalysts: A Combined Experimental and Computational Study

A sequence of Cr-doped NiMnOx layered double oxide catalysts was synthesized through coprecipitation and applied in selective catalytic reduction of NO with ammonia (NH3-SCR). The catalytic performance for NO reduction was enhanced by tuning the Ni/Mn/Cr molar ratios of the Ni1Mn1Crx-LDO precursors (x = 1, 2, 3); notably, Ni1Mn1Cr2-LDO achieved over 90% NO conversion and N2 selectivity within the temperature range of 150-300 °C. Moreover, Ni1Mn1Cr2-LDO demonstrated significant resistance to SO2 and H2O along with exceptional stability. From the results of the characterization of the physicochemical properties of the catalysts, the presence of Cr species in Ni1Mn1Crx-LDO may enhance the surface acidity and reducibility. Additionally, higher amounts of Mn4+, Ni3+, Cr3+, and surface-adsorbed oxygen species were detected on the Ni1Mn1Cr2-LDO catalyst. Through in situ DRIFTS experiments, the promotion of the NH3-SCR process on Ni1Mn1Cr2-LDO was confirmed to involve a combination of Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Oxidative Dehydrogenation of Ethane with CO2 over Mo/LDO Catalyst: The Active Species of Mo Controlled by LDO

A series of the layered double oxides supported molybdenum oxide catalysts were synthesized and evaluated in the oxidative dehydrogenation of ethane with CO2 (CO2-ODHE). The 22.3 wt% Mo/LDO catalyst delivered a 92.3%selectivity to ethylene and a 7.9% ethane conversion at relatively low temperatures. The molybdenum oxide catalysts were fully characterized by XRD, BET, SEM, TEM, UV–vis, Raman TG, and XPS. Isolated [MoO4]2− dominated on the surface of the fresh 12.5 wt% Mo/LDO catalyst. With the increase of the Mo content, the Mo species transformed from [MoO4]2− to [Mo7O24]6− and [Mo8O26]4− on the 22.3 wt% and 30.1 wt% Mo/LDO catalysts, respectively. The redox mechanism was proposed and three Mo species including [MoO4]2−, [Mo7O24]6−, and [Mo8O26]4− showed quite different functions in the CO2-ODHE reaction: [MoO4]2−, with tetrahedral structure, preferred the non-selective pathway; [Mo7O24]6−, with an octahedral construction, promoted the selective pathway; and the existence of [Mo8O26]4− reduced the ability to activate ethane. This work provides detailed insights to further understand the relationship between structure–activity and the role of surface Mo species as well as their aggregation state in CO2-ODHE.

DeNO x performance enhancement of Cu-based oxides via employing a TiO2 phase to modify LDH precursors

CuAl-LDO, CuAl-LDO/TiO2 and CuAl-LDO/TiO2NTs catalysts were obtained from TiO2 modified LDHs precursor which were prepared by in situ assembly method. Then catalysts were evaluated in the selective catalytic reduction of NO x with NH3(NH3-SCR), and the results showed that the CuAl-LDO/TiO2NTs catalyst exhibited preferable deNO x performance (more than 80% NO x conversion and higher than 90% N2 selectivity at a temperature range of 210-330 °C) as well as good SO2 resistance. With the aid of series of characterizations such as XRD, N2 adsorption/desorption, XPS, NH3-TPD, H2-TPR, and in situ DRIFTS, it could be concluded that, doping TiO2NTs afforded the catalyst larger specific surface area, more abundant surface chemisorption oxygen species and more excellent redox performance. Meanwhile, In situ DRIFTS evidenced that CuAl-LDO/TiO2NTs catalyst has a strong adsorption capacity for the reaction gas, which is more conducive to the progress of the SCR reaction.

Surface chemical functionality of carbon dots: influence on the structure and energy storage performance of the layered double hydroxide

As a kind of zero-dimensional material, carbon dots (CDs) have become a kind of promising novel material due to their incomparable unique physical and chemical properties. Despite the optical properties of CDs being widely studied, their surface chemical functions are rarely reported. Here we propose an interesting insight into the important role of surface chemical properties of CDs in adjusting the structure of the layered double hydroxide (LDH) and its energy storage performance. It was demonstrated that CDs with positive charge (p-CDs) not only reduce the size of the flower-like LDH through affecting the growth of LDH sheets, but also act as a structure stabilizer. After calcination, the layered double oxide (LDO) maintained the morphology of the LDH and prevented the stacking of layers. And the superiority of the composite in lithium-ion batteries (LIBs) was demonstrated. When used as an anode of LIBs, composites possess outstanding specific capacity, cycle stability and rate performance. It presents the discharge capacity of 1182 mA h g-1 and capacity retention of 94% at the current density of 100 mA g-1 after 100 cycles. Our work demonstrates the important chemical functions of CDs and expands their future applications.

Enhancement of NH3-SCR performance of LDH-based MMnAl (M = Cu, Ni, Co) oxide catalyst: influence of dopant M

Transition metal (Cu, Ni, Co) doped MnAl mixed oxide catalysts were prepared through a novel method involving the calcination of hydrotalcite precursors for the selective catalytic reduction of NO x with NH3 (NH3-SCR). The effects of transition metal modification were confirmed by means of XRD, BET, TEM, XPS, NH3-TPD, and H2-TPR measurements. Experimental results evidenced that CoMnAl-LDO presented the highest NO x removal efficiency of over 80% and a relatively high N2 selectivity of over 88% in a broad working temperature range (150-300 °C) among all the samples studied. Moreover, the CoMnAl-LDO sample possessed better stability and excellent resistance to H2O and SO2. The reasons for such results could be associated with the good dispersion of Co3O4 and MnO x , which could consequently provide optimum redox behavior, plentiful acid sites, and strong NO x adsorption ability. Furthermore, dynamics calculations verified the meaningful reduction in apparent activation energy (E a) for the CoMnAl-LDO sample, which is in agreement with the DeNO x activity.