Bauxite-supported Transition Metal Oxides: Promising Low-temperature and SO2-tolerant Catalysts for Selective Catalytic Reduction of NOx

Selective Lattice Doping Enables a Low-Cost, High-Capacity and Long-Lasting Potassium Layered Oxide Cathode for Potassium and Sodium Storage

Layered transition metal oxides are highly promising host materials for K ions, owing to their high theoretical capacities and appropriate operational potentials. To address the intrinsic issues of KxMnO2 cathodes and optimize their electrochemical properties, a novel P3-type oxide doped with carefully chosen cost-effective, electrochemically active and multi-functional elements is proposed, namely K0.57Cu0.1Fe0.1Mn0.8O2. Compared to the pristine K0.56MnO2, its reversible specific is increased from 104 to 135 mAh g-1. In addition, the Cu and Fe co-doping triples the capacity under high current densities, and contributes to long-term stability over 500 cycles with a capacity retention of 68 %. Such endeavor holds the potential to make potassium-ion batteries particularly competitive for application in sustainable, low-cost, and large-scale energy storage devices. In addition, the cathode is also extended for sodium storage. Facilitated by the interlayer K ions that protect the layered structure from collapsing and expand the diffusion pathway for sodium ions, the cathode shows a high reversible capacity of 144 mAh g-1, fast kinetics and a long lifespan over 1000 cycles. The findings offer a novel pathway for the development of high-performance and cost-effective sodium-ion batteries.

Layered P3-Type K0.4Fe0.1Mn0.8Ti0.1O2 as a Low-Cost and Zero-Strain Electrode Material for both Potassium and Sodium Storage

Layered transition metal oxides are ideal Na⁺/K⁺ host materials due to their high theoretical capacities and appropriate working potentials, and the pursuit of cost-effective and environmentally friendly alternatives with high energy density and structural stability has remained a hot topic. Herein, we design and synthesize a low-cost and zero-strain cathode material, P3-type K_0.4Fe_0.1Mn_0.8Ti_0.1O₂, which demonstrates superior properties for both potassium and sodium storage. The cathode delivers a reversible potassium storage capacity of 117 mA h g^-1 at 20 mA g^-1 and a fast rate capability of 71 mA h g^-1 at 1000 mA g^-1. In situ X-ray diffraction reveals a solid-solution transition with a negligible volume change of 0.5% upon K⁺ insertion/deinsertion that ensures long cycling stability over 300 cycles. When the material is employed for sodium storage, a spontaneous ion-exchange process with Na⁺-containing electrolytes occurs. Thanks to the positive effects of the remaining K⁺ ions that protect the layered structure from collapse as well as expand the interlayer structure, and the resulting K_0.12Na_0.28Fe_0.1Mn_0.8Ti_0.1O₂ demonstrates a high sodium storage capacity of 160 mA h g^-1 and superior cycling stability with capacity retention of 81% after 300 cycles as well as fast kinetics.

An Electrochemical Approach for the Selective Detection of Cancer Metabolic Creatine Biomarker with Porous Nano-Formulated CMNO Materials Decorated Glassy Carbon Electrode

The facile wet-chemical technique was used to prepare the low-dimensional nano-formulated porous mixed metal oxide nanomaterials (CuO.Mn2O3.NiO; CMNO NMs) in an alkaline medium at low temperature. Detailed structural, morphological, crystalline, and functional characterization of CMNO NMs were performed by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. An efficient and selective creatine (CA) sensor probe was fabricated by using CMNO NMs decorated onto glassy carbon electrode (GCE) as CMNO NMs/GCE by using Nafion adhesive (5% suspension in ethanol). The relation of current versus the concentration of CA was plotted to draw a calibration curve of the CMNO NMs/GCE sensor probe, which was found to have a very linear value (r2 = 0.9995) over a large dynamic range (LDR: 0.1 nM~0.1 mM) for selective CA detection. The slope of LDR by considering the active surface area of GCE (0.0316 cm2) was applied to estimate the sensor sensitivity (14.6308 µAµM-1 cm-2). Moreover, the detection limit (21.63 ± 0.05 pM) of CMNO MNs modified GCE was calculated from the signal/noise (S/N) ratio at 3. As a CA sensor probe, it exhibited long-term stability, good reproducibility, and fast response time in the detection of CA by electrochemical approach. Therefore, this research technique is introduced as a promising platform to develop an efficient sensor probe for cancer metabolic biomarker by using nano-formulated mixed metal oxides for biochemical as well as biomedical research for the safety of health care fields.

Study on compositions of FCC flue gas and pollutant precursors from FCC catalysts

Fluid catalytic cracking (FCC) unit emits a large amount of flue gas, which is a major issue of environmental protection supervision. A spent FCC catalyst from a typical FCC unit was characterized by NMR, XPS, EA TGA and TPD-MS methods. XPS results presented that the nitrogen compounds in coke were pyridine nitrogen, pyrrole and quaternary nitrogen. Sulfur compounds in coke are in the form of thiophene and thiols. TGA and TPD-MS results indicated that the soft coke in the spent catalyst may decompose to small molecular such as NOx, SO₂ and HCN. NH₃ and HCN are mainly emitted due to the incomplete combustion. The flue gas from the FCC unit is monitored by different on-line monitoring instruments. Results showed that the existence of ammonia greatly affected the value of SO₂ during the venting process or instruments' inlet piping system, where saturated vapor in flue gas is partially condensed. The concentration of NH₃ and HCN is more than 100 ppm, which should be paid more attention to. Taken together, fourier transform infrared method was more applicable for monitoring FCC flue gas than non-dispersed infrared method and ultraviolet fluorescence method.

Low Temperature deNOx Catalytic Activity with C2H4 as a Reductant Using Mixed Metal Fe-Mn Oxides Supported on Activated Carbon

The selective catalytic reduction of NOx (deNOx) at temperatures less than or at 200 °C was investigated while using C2H4 as the reductant and mixed oxides of Fe and Mn supported on activated carbon; their activity was compared to that of MnOx and FeOx separately supported on activated carbon. The bimetallic oxide compositions maintained high NO conversion of greater than 80–98% for periods that were three times greater than those of the supported monometallic oxides. To examine potential reasons for the significant increases in activity maintenance, and subsequent deactivation, the catalysts were examined by using bulk and surface sensitive analytical techniques before and after catalyst testing. No significant changes in Brunauer-Emmett-Teller (BET) surface areas or porosities were observed between freshly-prepared and tested catalysts whereas segregation of FeOx and MnOx species was readily observed in the mono-oxide catalysts after reaction testing that was not detected in the mixed oxide catalysts. Furthermore, x-ray diffraction and Raman spectroscopy data detected cubic Fe3Mn3O8 in both the freshly-prepared and reaction-tested mixed oxide catalysts that were more crystalline after testing. The presence of this compound, which is known to stabilize multivalent Fe species and to enhance oxygen transfer reactions, may be the reason for the high and relatively stable NO conversion activity, and its increased crystallinity during longer-term testing may also decrease surface availability of the active sites responsible for NO conversion. These results point to a potential of further enhancing catalyst stability and activity for low temperature deNOx that is applicable to advanced SCR processing with lower costs and less deleterious side effects to processing equipment.

A Review of Low Temperature NH3-SCR for Removal of NOx

The importance of the low-temperature selective catalytic reduction (LT-SCR) of NOx by NH3 is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, these catalytic materials have some drawbacks, especially in terms of catalyst poisoning by H2O or/and SO2. Hence, the development of catalysts for the LT-SCR process is still under active investigation throughout seeking better performance. Extensive research efforts have been made to develop new advanced materials for this technology. This article critically reviews the recent research progress on supported transition and mixed transition metal oxide catalysts for the LT-SCR reaction. The review covered the description of the influence of operating conditions and promoters on the LT-SCR performance. The reaction mechanism, reaction intermediates, and active sites are also discussed in detail using isotopic labelling and in situ FT-IR studies.

Site-Selective Deposition of Reductive and Oxidative Dual Cocatalysts To Improve the Photocatalytic Hydrogen Production Activity of CaIn2S4 with a Surface Nanostep Structure

Photocatalytic hydrogen production from water exhibits great potential for solar energy conversion. In this work, using monoclinic CaIn₂S₄ with a surface nanostep structure as a model photocatalyst, we demonstrate a facile and efficient strategy for the construction of AO _x/AuCu/CaIn₂S₄ (A = Mn, Ni, and Pb) composites by site-selective photodeposition of the reductive cocatalyst AuCu alloy and oxidative cocatalyst AO _x on the edge and groove sites of CaIn₂S₄ nanosteps, respectively. Compared to single-cocatalyst composites (AuCu/CaIn₂S₄ and AO _x/CaIn₂S₄) and CaIn₂S₄, the simultaneous deposition of AuCu and AO _x spatially separate the photogenerated charges and the photocatalytic reaction sites, therefore effectively improving the separation efficiency of charge carriers. Meanwhile, the synergistic effect of AuCu and AO _x dual cocatalysts notably reduces the apparent activation energy for the photocatalytic hydrogen production reaction. These novel dual-cocatalyst composites show enhanced performance for hydrogen production under visible light irradiation. A high rate of hydrogen production of 95.75 mmol h^-1 g^-1 is achieved over the MnO _x/AuCu/CaIn₂S₄ composite with the deposition of 0.5 wt % AuCu and 0.2 wt % MnO _x. Our work sheds new lights on designing efficient photocatalytic materials with site-selective surface deposition of reductive and oxidative dual cocatalysts for solar energy conversion.

Performance of C2H4 Reductant in Activated-Carbon- Supported MnOx-based SCR Catalyst at Low Temperatures

Hydrocarbons as reductants show promising results for replacing NH3 in SCR technology. Therefore, considerable interest exists for developing low-temperature (<200 °C) and environmentally friendly HC-SCR catalysts. Hence, C2H4 was examined as a reductant using activated-carbon-supported MnOx-based catalyst in low-temperature SCR operation. Its sensitivity to Mn concentration and operating temperature was parametrically studied, the results of which showed that the catalyst activity followed the order of 130 °C > 150 °C > 180 °C with an optimized Mn concentration near 3.0 wt.%. However, rapid deactivation of catalytic activity also occurred when using C2H4 as the reductant. The mechanism of deactivation was explored and is discussed herein in which deactivation is attributed to two factors. The manganese oxide was reduced to Mn3O4 during reaction testing, which contained relatively low activity compared to Mn2O3. Also, increased crystallinity of the reduced manganese and the formation of carbon black occurred during SCR reaction testing, and these constituents on the catalyst’s surface blocked pores and active sites from participating in catalytic activity.

In situ-DRIFTS study: influence of surface acidity of rhenium-based catalysts in the metathesis of various olefins for propylene production

Various olefins including 1- and 2-butene, 2-pentene, and ethylene were used as the reactants for producing propylene by self- and cross-metathesis reactions at 60 °C on supported Re-based catalysts (4 wt% Re).

Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process

Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration.