Yifei Chen

DFT insights into the adsorption of NH3-SCR related small gases in Mn-MOF-74

Mn-MOF-74 has great potential to catalyze selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR). However, the reaction mechanism, in particular the adsorptive properties of key reactive species in Mn-MOF-74, remains ambiguous. Besides, the effects of impurities such as H2O and SO2 on the process need further investigation. In this paper, based on density functional theory (DFT) calculations, we studied the adsorption characteristics of six NH3-SCR related small gases, namely NH3, NO2, NO, O2, H2O and SO2. DFT results show that the Mn-MOF-74 structure can bind these molecules relatively strongly in the following order: NH3 > NO2 > NO > O2, allowing for subsequent NH3-SCR reaction. In addition, a possible pathway of NO conversion to NO2 was calculated. Investigation on competitive adsorption of NH3 and H2O, NH3 and SO2 reveals that both H2O and SO2 are probable to replace NH3 under certain conditions, indicating that the two impurity gases may affect the activity of the NH3-SCR reaction. Compared with H2O, SO2 can displace NH3 more easily and should not be neglected.

Catalytic activity of transition metal doped Cu(111) surfaces for ethanol synthesis from acetic acid hydrogenation: a DFT study

Transition metal (Co, Ni, Ru, Rh, Pd and Pt) doped Cu(111) models are selected to examine the effects of transition metals on Cu surface for ethanol synthesis from acetic acid hydrogenation using density functional theory (DFT) calculations. On these surfaces, the adsorption of the main intermediates and reaction barriers of key elementary steps are investigated. The calculation results indicate that oxophilic metals are projected to be more active in acetic acid adsorption and acetaldehyde adsorption compared to less-oxophilic metals. Those metals with larger C adsorption energies generally have better C–OH bond cracking activity. Additionally, a good linear Bronsted–Evans–Polanyi (BEP) correlation is established for predicting the preferences of C–OH bond scission of acetic acid on other metals. Finally, O–H bond formation in C2-oxygenates (CH3CO, CH3CHO, CH3CH2O) hydrogenation is examined on all these surfaces. The reactions are more likely to occur on less-oxophilic metal-doped Cu surfaces. Therefore, it appears to involve an intricate balance between C–OH cracking and O–H bond formation reactions. That means those metal-doped Cu-based catalysts that are capable of preferentially activating C–OH bond without considerably inhibiting O–H bond formation of C2-oxygenates are predicted to achieve optimum catalytic activity for ethanol synthesis from acetic acid hydrogenation. The results can provide theoretical guidance for related experiments as well as the designing of Cu-based catalysts for ethanol synthesis.

Selective Catalytic Reduction of NO x with NH 3 on Cu-BTC-derived Catalysts: Influence of Modulation and Thermal Treatment

In this work, copper-based metal organic frameworks Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylatle), were applied in the conversion of toxic oxynitride into nitrogen at low temperature. Scanning electron microscope (SEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XRD) and other characterization methods were employed to fully understand the properties of the catalysts. We introduced acetic acid into the synthesis process as the modulator of the crystal structure and morphology. The catalytic assessment indicated that compared with the prototype, modified Cu-MOFs materials obtain enhanced catalytic activity for the SCR reaction. Besides, several thermolysis experiments were conducted to explain structure–function relationship.

Metal-organic framework loaded manganese oxides as efficient catalysts for low-temperature selective catalytic reduction of NO with NH 3

A mild in-situ deposition method was used to fabricate Mn-based catalysts on a UiO-66 carrier for the selective catalytic reduction of NO by NH3 (NH3-SCR). The catalyst with 8.5 wt-% MnOx loading had the highest catalytic activity for NH3-SCR with a wide temperature window (100–290 °C) for 90% NO conversion. Characterization of the prepared MnOx/UiO-66 catalysts showed that the catalysts had the crystal structure and porosity of the UiO-66 carrier and that the manganese particles were well-distributed on the surface of the catalyst. X-ray photoelectron spectroscopy analysis showed that there are strong interactions between the MnOx and the Zr oxide secondary building units of the UiO-66 which has a positive effect on the catalytic activity. The 8.5 wt-% MnOx catalyst maintained excellent activity during a 24-h stability test and exhibited good resistance to SO2 poisoning.