Selective Catalytic Reaction Research Articles

Nb-Modified Mn–Fe–PILC Catalyst with Improved Resistance to Alkali Metals for the NH3–Selective Catalytic Reduction Reaction

Nb-Modified Mn–Fe–PILC Catalyst with Improved Resistance to Alkali Metals for the NH₃–Selective Catalytic Reduction Reaction

Selective catalytic oxidation of DMF over Cu-Ce/H-MOR by modulating the surface active sites

Selective catalytic oxidation of the hazardous DMF exhaust gas presents a significant challenge in balancing oxidation activity and products selectivity (CO, NOx, N2, etc.). It is found that Cu/H-MOR demonstrates superior performance for DMF oxidation compared to CuO on other supports (γ-Al2O3, HY, ZSM-5) in terms of product selectivity and stability. The geometric and electronic structures of CuO active sites in Cu/H-MOR have been regulated by CeO2 promoter, leading to an increase in the ratio of active CuO (highly dispersed CuO and Cu+ specie). As a result, the oxidation activity and stability of the Cu/H-MOR catalyst were enhanced for DMF selective catalytic oxidation. However, excessive CuO or CeO2 content led to decreased N2 selectivity due to over-high oxidation activity. It is also revealed that Ce3+ species, active CuO species, and surface acid sites play a critical role in internal selective catalytic reduction reaction during DMF oxidation. The 10Cu-Ce/H-MOR (1/4) catalyst exhibited both high oxidation activity and internal selective catalytic reduction activity due to its abundance of active CuO specie as well as Ce3+ species and surface acid sites. Consequently, the 10Cu-Ce/H-MOR (1/4) catalyst demonstrated the widest temperature window for DMF oxidation with high N2 selectivity. These findings emphasize the importance of surface active sites modification for DMF selective catalytic oxidation.

Effects of Cu species in Cu-SSZ-13 zeolites on the performance of NOx reduction reactions

In diesel vehicle exhaust after-treatment systems, high silica Cu-SSZ-13 has received increasing attention as a commercialized catalyst owing to its high efficiency in selective catalytic reduction reactions with NH3 (NH3-SCR). However, research on the regulation of Cu2+ species within metal active centers in the pore structure of chabazite (CHA)-type zeolite to improve catalytic performance lacks sufficient depth. Herein, SSZ-13 zeolite with various Al distributions was prepared by adjusting the proportion of N,N,N-Trimethyl-1-adamantanaminiumhydroxide (TMAdaOH) and Na in the initial gel. Moreover, three representative Cu-SSZ-13 catalysts with different Cu2+ species were synthesized via an ion exchange method. 23Na MAS NMR and NO adsorption infrared spectroscopy results revealed that with increasing Na content and decreasing TMAdaOH concentration in the initial gel, the number of paired Al in the CHA framework gradually increased. Consequently, this increased the number of Cu2+-2Z sites near six-membered ring (MR) and reduced the amount of [Cu(OH)]+-Z sites near eight-MR. The fresh Cu-SSZ-13 catalyst, with a moderate amount of Cu2+-2Z and [Cu(OH)]+-Z, exhibited optimal catalytic performance across the entire temperature window. After hydrothermal aging, Cu-SSZ-13 with a higher concentration of Cu2+-2Z species featured optimal performance among all Cu-SSZ-13 catalysts above 400 °C. These findings indicated the significance of balancing the amount of both Cu2+-2Z and [Cu(OH)]+-Z in the Cu-SSZ-13 zeolite. Additionally, the results elucidated the reaction intermediates involved in the NH3-SCR process catalyzed by Cu-SSZ-13 with various Cu species.

Unravelling the Role of Zr–Laponite Supports in Enhancing the Activity of a MnNi Catalyst for the Low-Temperature NH3-Selective Catalytic Reduction Reaction

Unravelling the Role of Zr–Laponite Supports in Enhancing the Activity of a MnNi Catalyst for the Low-Temperature NH₃-Selective Catalytic Reduction Reaction

Surface Engineered Single-atom Systems for Energy Conversion.

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

Investigating NH3-SCR coupled with CO oxidation reaction mechanisms on titanium nanotube-loaded CuMnFe composite metal catalysts

NOx and CO are the primary air pollutants emitted from sintering flue gas, and their effective treatment is crucial. However, achieving good N2 selectivity with the CuMnFe composite metal oxide catalyst alone is challenging due to its oxidizing nature. Hence, in this study, titanium dioxide nanotubes were employed as carriers for the catalyst. CuMnFe composite metal oxide catalysts supported on titanium dioxide nanotubes were prepared using the co-precipitation method. The optimized catalysts demonstrated excellent performance, maintaining over 90% conversion of NOx and CO at low temperatures ranging from 120 to 200 ℃. Furthermore, significant improvement in N2 selectivity was achieved using these catalysts. Characterization results revealed several positive effects of incorporating titanium dioxide nanotube carriers into the catalyst. Firstly, it efficiently reduced the mobility of adsorbed oxygen on the catalyst surface, thus decreasing its oxidation capacity. Secondly, the addition of carriers helped balance the acidity on the catalyst surface, leading to an increase in Lewis acid sites. These modifications in the catalyst's surface properties proved advantageous for the selective catalytic reduction reaction. Moreover, the mechanisms of NH3-SCR and CO oxidation over the catalysts were extensively studied using DRIFTS. The results demonstrated that the CO oxidation reaction followed the Mars-van Krevelen mechanism, with a competitive adsorption relationship observed between O2 and CO at the active sites. On the other hand, the NH3-SCR reaction primarily followed the Eley-Rideal mechanism, with minimal occurrence of the Langmuir-Hinshelwood mechanism in the SCR reaction. The presence of NH3 inhibits CO adsorption at the active site, resulting in decreased CO oxidation performance in the NH3-SCR-coupled CO oxidation reaction at low temperatures. Nevertheless, NH3-SCR can enhance NO conversion by utilizing some of the latent heat generated from the exothermic CO oxidation.

Copper-exchanged SUZ-4 zeolite catalysts for selective catalytic reduction of NOx

The copper-exchanged SUZ-4 zeolite with optimal compositions exhibits comparable catalytic properties to commercial Cu-SSZ-13 for the selective catalytic reduction reaction.

Enhanced SO2 resistance of NiFe/CeO2 catalyst by adding WS2 for CO-assisted selective catalytic reduction reaction

Selective catalytic reduction (SCR) is an effective NOx reduction method. Recently, research has been conducted on simultaneously removing NOx and CO using passive SCR technology that consumes CO gas that is normally generated in industrial combustion processes (designated as CO-SCR). SO2 gas in industrial flue gas can compete with NOx and CO, leading to catalyst deactivation and a shortened lifespan. Catalysts with resistance to the sulfur present in industrial processes are crucial for CO-SCR. Therefore, this study aimed to develop a catalyst resistant to the SO2 present in exhaust gas; specifically, WS2 which has excellent chemical stability, was added to a transition metal-based catalyst NiFe/CeO2 and the CO-SCR activity of the unmodified and WS2-incorporated catalysts (NiFe/CeO2 and NiFe/WS2-CeO2, respectively) were examined. NiFe/WS2-CeO2 (1 wt% WS2 content) exhibited a high NOx conversion rate of more than 80% in a sulfur atmosphere. The addition of WS2 to NiFe/CeO2 improved its CO adsorption capacity and catalytic reduction properties by 1.63 and 1.28 times, respectively, thereby promoting the catalytic performance. Fourier-transform infrared analysis revealed that NiFe/WS2-CeO2 was more resistant to sulfur poisoning than NiFe/CeO2. These findings can be leveraged to develop sulfur-resistant catalysts for eliminating NOx and CO from industrial flue gas.

Fabrication of Chiral Plasmonic Photocatalyst By Circularly Polarized Light and Enantioselective Hydrogen Generation Activity

Introducing chirality in nanostructures has been explored actively in various field, such as sensing, optoelectronics and catalysts, due to its unique chiroptical properties. Especially in photochemistry, considering the synergistic interaction between chiral plasmonics and polarized light, they can be utilized to improve efficiency and selectivity of catalytic reaction. In this work, we synthesized chiral plasmonic photocatalysts, (R)-,(L)- Au/C3N4, through photoreduction of gold precursor on C3N4 substrate under the irradiation of circularly polarized light (CPL) as a means to induce chirality. Then, we demonstrated that the efficiency of hydrogen generation can be increased by matching the chirality of the CPL with the photocatalyst, which was 2-fold enhanced than chiral mismatching conditions. This can be explained by the asymmetric hot carrier formation of chiral plasmonic structures under CPL excitation. Also, the reactivity of water molecule with photocatalyst surface was confirmed through in-situ FT-IR, showing the enhanced interaction under chiral matching conditions. This study could pave the way for advancing chiral light-matter interactions and explore the application of novel device, particularly toward chiral-induced photocatalytic performance.

Designing synergies between hybrid renewable energy systems and ecosystems developed by different afforestation approaches

In this study, we explore the possibility of techno-ecological synergy (TES) based sustainable design of hybrid renewable energy systems (HRES) and their surrounding ecosystems to mitigate emissions. We consider an HRES system with a photovoltaic cell, wind turbine, fuel cell, electrolyzer, and diesel generator. The NO2 and CO2 emissions from HRES have been conventionally treated using a selective catalytic reactor and monoethanolamine (MEA), respectively. However, a forest ecosystem can naturally uptake NO2 and CO2. Therefore, we have considered the forest ecosystem as an additional unit operation in this study and its growth dynamics have been incorporated in the system design. Thus, we analyze two approaches to remediate emissions from the HRES: (1) technological approach — SCR and MEA, (2) TES approach — forest ecosystem in tandem with technology. Unlike previous TES design studies, we focus on cities in India and compare a traditional method for forest restoration and a faster Miyawaki method considering their growth dynamics. Furthermore, we consider the case of social forestry, which is relevant in developing countries. Here, the trees are pruned, which increases the pollution uptake rate. We find that the emission abatement technology cannot be removed from the system as it is needed for seasons wherein trees shed their leaves; therefore a periodic profile of technology utilization for emissions abatement is observed. We find the TES approach to be more economically feasible for pollution uptake than a purely technology based approach for the sustainable operation of HRES at Delhi and Chennai in India, respectively. Based on this, the annualized cost of electricity generation is found to be 15% less than the base case. Moreover, the study reveals that annualized cost of electricity generation associated with the Miyawaki method is 13% less than the traditional reforestation method for attaining TES designs.

Expanding the boundary of biorefinery: long-chain heteroatom-containing chemicals from biomass

Biomass is regarded as the largest renewable carbon resource on earth. Various biomass-based value-added chemicals, transportation fuels and carbon-based functional materials can be obtained through selective catalytic systems and reaction processes. The production of long-chain heteroatom-containing chemicals from biomass as a relatively new direction in the field of biorefinery has received significant attention in recent years. The process of producing long-chain heteroatom-containing chemicals involves two steps, namely CC coupling to long-chain intermediates and further transformation into long-chain heteroatom-containing chemicals. In this perspective, we discuss the strategies for the production of long-chain heteroatom-containing chemicals, with a focus on the transformation strategies of long-chain intermediates into long-chain heteroatom-containing chemicals. Finally, our insights into future recommendations in this promising field are provided.

Mechanistic Study on Steric Activity Interplay of Olefin/Polar Monomers for Industrially Selective Late Transition Metal Catalytic Reactions.

A significant issue in developing metal-catalyzed plastic polymer materials is obtaining distinctive catalytic characteristics to compete with current plastics in industrial commodities. We performed first-principle DFT calculations on the key insertion steps for industrially important monomers, vinyl fluoride (VF) and 3,3,3-trifluoropropene (TFP), to explain how the ligand substitution patterns affect the complex's polymerization behaviors. Our results indicate that the favorable 2,1-insertion of TFP is caused by less deformation in the catalyst moiety of the complexes in contrast to the 1,2-insertion mode. In contrast to the VF monomer, the additional interaction between the fluorine atoms of 3,3,3-trifluoropropene and the carbons of the catalyst ligands also contributed to favor the 2,1-insertion. It was found that the regioselectivity of the monomer was predominated by the progressive alteration of the catalytic geometry caused by small dihedral angles that were developed after the ligand-monomer interaction. Based on the distribution of the 1,2- and 2,1-insertion products, the activity and selectivity were influenced by the steric environment surrounding the palladium center; thus, an increased steric bulk visibly improved the selectivity of the bulkier polar monomer (TFP) during the copolymerization mechanism. In contrast, better activity was maintained through a sterically less hindered Pd metal center; the calculated moderate energy barriers showed that a catalyst with less steric hindrance might provide an opportunity for a wide range of prospective industrial applications.

Enhancing performance of Fe-SSZ-13 and Cu-Fe-SSZ-13 zeolites for selective catalytic reduction reaction via post-treatment method

Fe-SSZ-13 zeolites were prepared via post-treatment method by using different concentrations of HNO3 solution. Prior to HNO3 treatment, Fe-SSZ-13 was synthesized by using Fe(III)-ethylenediaminetetraacetic acid as iron source. The evaluation of ammonia-assisted selective catalytic reduction reaction indicates that Fe-SSZ-13 and Cu-Fe-SSZ-13 after HNO3 treatment show enhanced catalytic performance compared with corresponding initial counterparts, respectively. Particularly, after hydrothermal ageing (HTA), Cu-Fe-SSZ-13-0.4-HTA with optimal HNO3 concentration of 0.4 M exhibits ∼5% higher NO conversion than Cu-Fe-SSZ-13-0-HTA at 150–250 °C and 450–550 °C. The superior NH3-SCR performance of HNO3-treated zeolites is attributed to that HNO3-treatment method can regulate the distribution of Fe species by decreasing FexOy and increasing isolated Fe3+ content.

Artificial Photosynthesis: Current Advancements and Future Prospects.

Artificial photosynthesis is a technology with immense potential that aims to emulate the natural photosynthetic process. The process of natural photosynthesis involves the conversion of solar energy into chemical energy, which is stored in organic compounds. Catalysis is an essential aspect of artificial photosynthesis, as it facilitates the reactions that convert solar energy into chemical energy. In this review, we aim to provide an extensive overview of recent developments in the field of artificial photosynthesis by catalysis. We will discuss the various catalyst types used in artificial photosynthesis, including homogeneous catalysts, heterogeneous catalysts, and biocatalysts. Additionally, we will explore the different strategies employed to enhance the efficiency and selectivity of catalytic reactions, such as the utilization of nanomaterials, photoelectrochemical cells, and molecular engineering. Lastly, we will examine the challenges and opportunities of this technology as well as its potential applications in areas such as renewable energy, carbon capture and utilization, and sustainable agriculture. This review aims to provide a comprehensive and critical analysis of state-of-the-art methods in artificial photosynthesis by catalysis, as well as to identify key research directions for future advancements in this field.

Deactivation induced by metal sulfate over MnCeOx catalyst in NH3-SCR reaction at low temperature

Sulfate adsorption is one of the factors that cause the poisoning of catalyst in the low-temperature NH3 selective catalytic reduction reaction (NH3-SCR). In this paper, by controlling the co-adsorption time of SO2 and O2 at 150 °C, a range of sulfated MnCeOx catalysts with different contents of metal sulfate species were prepared to reveal the influence of metal sulfate species content on the catalytic performances and reaction mechanisms at low temperature. The catalytic activity below 250 °C rapidly decreases with increasing metal sulfate species content. The results of characterizations shed light on the reduction of specific surface area, Mn4+ and Ce3+ content, and redox ability of MnCeOx owing to the formation of metal sulfate species. Further experiments reveal that metal sulfate species preferentially absorb on MnOx domains rather than on CeO2 domains, and the adsorbed metal sulfate species can suppress the Eley-Rideal and the Langmuir–Hinshelwood reaction mechanisms over the sulfated MnCeOx. All the above results are detrimental to the activity of sulfated MnCeOx in the low-temperature NH3-SCR reaction.

Insights of active sites separation mechanism for highly efficient electrocatalytic N2 reduction to ammonia over glucose-induced metallic MoS2

Substituting the Haber-Bosch process with electrocatalytic N2 reduction reaction (NRR) is expected to be realized by optimizing the active sites to boost the sluggish N2 adsorption and the hydrogenation process without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, a phase engineering strategy for MoS2 toward NRR is reported. The 1T phase are found to enhance the NRR activity with strong N2 adsorption. Then, the active site separation can weaken the competitive adsorption between H+ and N2 reactant on the Mo-edge, improving the NRR selectivity. More importantly, the HER selective basal plane can serve as an H-provider to further accelerate the hydrogenation process of NRR. The optimal MoS2/C-0.4 possesses a high ammonia yield rate of 80.38 μg h–1 mg–1cat. and Faradaic efficiency (FE) of 23.76%, outperforming almost all MoS2-based electrocatalysts and beyond. This work sheds light on synchronizing the catalytic activity and selectivity for catalytic reactions.

Low-temperature NH3 abatement via selective oxidation over a supported copper catalyst with high Cu+ abundance

Selective catalytic NH3-to-N2 oxidation (NH3-SCO) is highly promising for abating NH3 emissions slipped from stationary flue gas after-treatment devices. Its practical application, however, is limited by the non-availability of low-cost catalysts with high activity and N2 selectivity. Here, using defect-rich nitrogen-doped carbon nanotubes (NCNT-AW) as the support, we developed a highly active and durable copper-based NH3-SCO catalyst with a high abundance of cuprous (Cu+) sites. The obtained Cu/NCNT-AW catalyst demonstrated outstanding activity with a T50 (i.e. the temperature to reach 50% NH3 conversion) of 174°C in the NH3-SCO reaction, which outperformed not only the Cu catalyst supported on N-free O-functionalized CNTs (OCNTs) or NCNT with less surface defects, but also those most active Cu catalysts in open literature. Reaction kinetics measurements and temperature-programmed surface reactions using NH3 as a probe molecule revealed that the NH3-SCO reaction on Cu/NCNT-AW follows an internal selective catalytic reaction (i-SCR) route involving nitric oxide (NO) as a key intermediate. According to mechanistic investigations by X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray absorption spectroscopy, the superior NH3-SCO performance of Cu/NCNT-AW originated from a synergy of surface defects and N-dopants. Specifically, surface defects promoted the anchoring of CuO nanoparticles on N-containing sites and, thereby, enabled efficient electron transfer from N to CuO, increasing significantly the fraction of SCR-active Cu+ sites in the catalyst. This study puts forward a new idea for manipulating and utilizing the interplay of defects and N-dopants on carbon surfaces to fabricate Cu+-rich Cu catalysts for efficient abatement of slip NH3 emissions via selective oxidation.

Highly Selective Activation of C–H Bond and Inhibition of C–C Bond Cleavage by Tuning Strong Oxidative Pd Sites

Improving the product selectivity meanwhile restraining deep oxidation still remains a great challenge over the supported Pd-based catalysts. Herein, we demonstrate a universal strategy where the surface strong oxidative Pd sites are partially covered by the transition metal (e. g., Cu, Co, Ni, and Mn) oxide through thermal treatment of alloys. It could effectively inhibit the deep oxidation of isopropanol and achieve the ultrahigh selectivity (>98%) to the target product acetone in a wide temperature range of 50-200 °C, even at 150-200 °C with almost 100% isopropanol conversion over PdCu1.2/Al2O3, while an obvious decline in acetone selectivity is observed from 150 °C over Pd/Al2O3. Furthermore, it greatly improves the low-temperature catalytic activity (acetone formation rate at 110 °C over PdCu1.2/Al2O3, 34.1 times higher than that over Pd/Al2O3). The decrease of surface Pd site exposure weakens the cleavage for the C-C bond, while the introduction of proper CuO shifts the d-band center (εd) of Pd upward and strengthens the adsorption and activation of reactants, providing more reactive oxygen species, especially the key super oxygen species (O2-) for selective oxidation, and significantly reducing the barrier of O-H and β-C-H bond scission. The molecular-level understanding of the C-H and C-C bond scission mechanism will guide the regulation of strong oxidative noble metal sites with relatively inert metal oxide for the other selective catalytic oxidation reactions.

Selectively Permeable FeOOH Amorphous Layer Coating CdS for Enhancing Photocatalytic Conversion of Benzyl Alcohol and Selectivity to Benzaldehyde.

The development of new strategies to improve reaction efficiency and light utilization is one of the biggest challenges in photosynthetic chemistry. Dynamics control, particularly tuning the adsorption/desorption of reactants and products, is an ideal way to improve the conversion and selectivity in catalytic reactions, but it is rarely studied for photocatalytic organic synthesis. This study concerns the design of an amorphous FeOOH coating to decorate CdS photocatalyst to control the adsorption and desorption of reactants and products to improve reaction efficiency for the photocatalytic conversion of benzyl alcohol (BA) into benzaldehyde (BAD). The best conversion of the core-shell photocatalyst is 74.1 % in 2 h, together with >99.9 % selectivity to BAD, and the photocatalyst exhibits response above 600 nm, which is the longest active wavelength reported for the reaction. Further data illustrate that the amorphous FeOOH coating enables selective sorption of BA/BAD molecules by H-bonding interactions, which may result in the excellent performance. Construction of amorphous coating layers and understanding the selective permeability may provide a new strategy for the design of more efficient photocatalytic systems for organic synthesis.

Evaluating the performance of static mixers using the -number: the case of the Koflo® mixer

Static mixers (SMs) are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or some combination of these. Accurately evaluating the performance of SMs is critical for the appropriate selection of these devices. Traditional approaches involve parameters that separately evaluate the mixing level and the energy spent in mixing (i.e., pressure drop) but do not account for both simultaneously. The -number has been recently proposed as a means to simultaneously evaluate the quality of mixing as well as the pressure drop across the static mixer (SM). This work demonstrates an implementation of the -number by evaluating the performance of a KOFLO® static mixer (KSM) for mixing water vapor and air via Computational Fluid Dynamics (CFD), for Schmidt number of approximately unity. Pipe and mixer sizes as well as inlet profile distribution were varied. A single-element KSM was used based on the impetus of our study: Selective Catalytic Reactor (SCR) applications, which requires minimization of the pressure drop. The results are shown to be reasonably comparable with respect to previous works containing experimental data.