Atom Pairing Enhances Sulfur Resistance in Low-Temperature SCR via Upshifting the Lowest Unoccupied States of Cerium.

Environmentally benign cerium-based catalysts are promising alternatives to toxic vanadium-based catalysts for controlling NOx emissions via selective catalytic reduction (SCR), but conventional cerium-based catalysts unavoidably suffer from SO2 poisoning in low-temperature SCR. We develop a strongly sulfur-resistant Ce1+1/TiO2 catalyst by spatially confining Ce atom pairs to different anchoring sites of anatase TiO2(001) surfaces. Experimental results combined with theoretical calculations demonstrate that strong electronic interactions between the paired Ce atoms upshift the lowest unoccupied states to an energy level higher than the highest occupied molecular orbital (HOMO) of SO2 so as to be catalytically inert in SO2 oxidation but slightly lower than HOMO of NH3 so that Ce1+1/TiO2 has desired ability toward NH3 activation required for SCR. Hence, Ce1+1/TiO2 shows higher SCR activity and excellent stability in the presence of SO2 at low temperatures with respect to supported single Ce atoms. This work provides a general strategy to develop sulfur-resistant catalysts by tuning the electronic states of active sites for low-temperature SCR, which has implications for practical applications with energy-saving requirements.

A simple and rapid method for isolating high-quality RNA from kenaf with high polysaccharide and polyphenol contents.

The extraction of high-quality RNA from kenaf is essential for genetic and molecular biology research. However, the presence of high levels of polysaccharide and polyphenol compounds in kenaf poses challenges for RNA isolation. We proposed a simplified, time-saving and cost-effective method for isolating high quantities of RNA from various kenaf tissues. This method exhibited superior efficiency in RNA isolation compared with the conventional cetyltrimethylammonium bromide method and demonstrated greater adaptability to different samples than commercial kits. Furthermore, the high-quality RNA obtained from this method was successfully utilized for RT-PCR, real-time RT-PCR and northern blot analysis. Moreover, this proposed protocol also enables the acquisition of both high-quality and -quantity gDNA through RNase A treatment. In addition, the effectiveness of this approach in isolating high-quality RNA from other plant species has been experimentally confirmed.

NO Selective Catalytic Reduction over Atom-Pair Active Sites Accelerated via In Situ NO Oxidation.

Selective catalytic reduction (SCR) of NOx with NH3 is the most efficient technology for NOx emissions control, but the activity of catalysts decreases exponentially with the decrease in reaction temperature, hindering the application of the technology in low-temperature SCR to treat industrial stack gases. Here, we present an industrially practicable technology to significantly enhance the SCR activity at low temperatures (<250 °C). By introducing an appropriate amount of O3 into the simulated stack gas, we find that O3 can stoichiometrically oxidize NO to generate NO2, which enables NO reduction to follow the fast SCR mechanism so as to accelerate SCR at low temperatures, and, in particular, an increase in SCR rate by more than four times is observed over atom-pair V1-W1 active sites supported on TiO2(001) at 200 °C. Using operando SCR tests and in situ diffuse reflectance infrared Fourier transform spectra, we reveal that the introduction of O3 allows SCR to proceed along a NH4NO3-mediated Langmuir-Hinshelwood model, in which the adsorbed nitrate species speed up the re-oxidation of the catalytic sites that is the rate-limiting step of SCR, thus leading to the enhancement of activity at low temperatures. This technology could be applicable in the real stack gas conditions because O3 exclusively oxidizes NO even in the co-presence of SO2 and H2O, which provides a general strategy to improve low-temperature SCR efficacy from another perspective beyond designing catalysts.

An Atom-Pair Design Strategy for Optimizing the Synergistic Electron Effects of Catalytic Sites in NO Selective Reduction.

Effective adsorption and speedy surface reactions are vital requirements for efficient active sites in catalysis, but it remains challenging to maximize these two functions simultaneously. We present a solution to this issue by designing a series of atom-pair catalytic sites with tunable electronic interactions. As a case study, NO selective reduction occurring on V1 -W1 /TiO2 is chosen. Experimental and theoretical results reveal that the synergistic electron effect present between the paired atoms enriches high-energy spin charge around the Fermi level, simultaneously rendering reactant (NH3 or O2 ) adsorption more effective and subsequent surface reactions speedier as compared with single V or W atom alone, and hence higher reaction rates. This strategy enables us to rationally design a high-performance V1 -Mo1 /TiO2 catalyst with optimized vanadium(IV)-molybdenum(V) electronic interactions, which has exceptional activity significantly higher than the commercial or reported catalysts.

Valence states of single Au atoms dictate the catalytic activity of Au1/CeO2(100).

We tune the valence state of single Au atoms anchored on CeO2(100) by treating the catalyst in H2 at different temperatures and obtain a series of Au1/CeO2(100). The transition from Au1+0.9 to Au1+0.3 leads to an enhancement of the CO oxidation activity of Au1/CeO2(100) by one order of magnitude. This work is of significance for an in-depth understanding of reaction mechanisms and rational design of high-performance catalysts.

First report of root rot caused by Fusarium solani on roselle in Nanning, Guangxi, China.

Roselle (Hibiscus sabdariffa L.) is an annual herbaceous plant in the Malvaceae family with high anthocyanin and is widely cultivated in Nanning, Guangxi of China due to its economic and nutritional importance. In August 2021, a severe root rot disease with incidence of 42.4% (860 plants in the field) was observed in roselle plants in an open-field crop in Nanning (108°33"E, 22°84"N), Guangxi, China. The roots of the diseased plants were discolored and rotten, and the xylem became black, extending along the main root to the junction of the rhizomes. The above-ground symptoms were leaf yellowing, vascular tissue browning, wilting and death. Three diseased samples were rinsed thoroughly with sterile distilled water, cut with a sterile scalpel into approximately 0.5-cm pieces, surface disinfested with 75% ethanol for one minute, rinsed 3-4 times with sterile water, and finally incubated on potato dextrose agar (PDA) at 28 °C in the dark for 3 days. Emerging colonies were transferred to new PDA two-three times until a single colony was obtained. The aerial mycelium was initially white, turning pale yellow after 5 days of growth on PDA. Microscopic observations revealed that microconidia were hyaline and ovoid with sizes of 5.13 to 15.12 and 2.50 to 4.20 µm (average 9.02, 3.32 µm, n=30). Macroconidia were falciform with 3- to 4-septate, with sizes of 19.08 to 24.35 and 4.5 to 8.00 µm (average 24.35 and 5.23 µm, n=30). The morphological characteristics of the microscopic images were identical to those described for Fusarium solani (Leslie and Summerell 2006). A representative isolate (GXRST29) was selected for DNA extraction for further characterization. The internal transcribed spacer rRNA regions (ITSs), beta tubulin gene sequence and a fragment of the translation elongation factor 1-alpha (EF 1-α) gene sequence were amplified using the primer pairs ITS1/ITS4 (Chehri 2014), Bt-1/Bt-2 (Wang et al. 2014) and EF1-F/EF2-R (O'Donnell et al. 2010), respectively. PCR products were sequenced and deposited in GenBank (accession Nos. OL314654, ON157430 and ON157431, respectively). BLASTn analysis showed that the ITS sequence had 96.99% homology with sequence of F. solani (NR 163531), and 99.26% for Fusarium cf. solani (MG775565) obtained from Homo sapiens. The beta tubulin sequence had 97.96% similarity with BLAST sequence of F. solani (MN295052.1) and EF 1-α gene had 100% identity to published F. solani (MN977912.1). The fungus was identified as F. solani. Five roselle plants at the 5-leaf stage were artificially inoculated by root dipping into a 106-107-mL-1 spore suspension of the isolated GXRST29 for pathogenicity testing. The experiment was conducted three times, and the negative controls were replaced with sterile water. Compared to the control, the growth of plants was significantly inhibited, leaves turned yellow, plants dwarfed and wilted, and roots decayed three days post-inoculation. One week post-inoculation, all plants exhibited symptoms similar to those observed in the field, and F. solani was steadily reisolated from those diseased plants, while no positive isolations were obtained in the controls. F. solani has been reported to cause root rot on roselle in Upper Egypt (Hassan et al. 2014) and lisianthus in China (Xiao et al. 2018). To our knowledge, however, this is the first report of Fusarium wilt caused by F. solani in roselle plants in Nanning, Guangxi, China, and could result in severe crop losses.

Abatement of Nitrogen Oxides via Selective Catalytic Reduction over Ce1-W1 Atom-Pair Sites.

Environmentally benign CeO2-WO3/TiO2 catalysts are promising alternatives to commercial toxic V2O5-WO3/TiO2 for controlling NOx emission via selective catalytic reduction (SCR), but the insufficient catalytic activity of CeO2-WO3/TiO2 catalysts is one of the obstacles in their applications because of a lack of an in-depth understanding of the CeO2-WO3 interactions. Herein, we design a Ce1-W1/TiO2 model catalyst by anchoring Ce1-W1 atom pairs on anatase TiO2(001) to investigate the synergy between Ce and W in SCR. A series of characterizations combined with density functional theory calculations and in situ diffuse-reflectance infrared Fourier-transform experiments reveal that there exists a strong electronic interaction within Ce1-W1 atom pairs, leading to a much better SCR performance of Ce1-W1/TiO2 compared with that of Ce1/TiO2 and W1/TiO2. The Ce1-W1 synergy not only shifts down the lowest unoccupied states of Ce1 near the Fermi level, thus enhancing the abilities in adsorbing and oxidizing NH3 but also makes the frontier orbital electrons of W1 delocalized, thus accelerating the activation of O2. The deep insight of the Ce-W synergy may assist in the design and development of efficient catalysts with an SCR activity as high as or even higher than V2O5-WO3/TiO2.

Nucleo-cytoplasmic interactions affect the 5' terminal transcription of mitochondrial genes between the isonuclear CMS line UG93A and its maintainer line UG93B of kenaf (Hibiscus cannabinus).

Gene expression and translation in plant mitochondria remain poorly understood due to the complicated transcription of its mRNA. In this study, we report the 5' and 3' RNA extremities and promoters of five mitochondrial genes, atp1, atp4, atp6, atp9, and cox3. The results reveal that four genes (atp1, atp4, atp6, and cox3) are transcribed from multiple initiation sites but with a uniform transcript at the 3' end, indicating that heterogeneity of the 5' end is a common feature in the transcription of kenaf mitochondrial genes. Furthermore, we found that the transcription initiation sites of these four genes are significantly different in UG93A, UG93B, and the F1 hybrid. These data indicate that nuclear loci and unknown transcription factors within the mitochondria of different cytoplasmic types may be involved in mitochondrial transcription. Promoter architecture analysis showed that the promoter core sequences are conserved in the kenaf mitochondrial genome but are highly divergent, suggesting that these elements are essential for the promoter activity of mitochondrial genes in kenaf. Our results reveal that the heterogeneity of the 5' end and uniformity at the 3' end are common transcriptional features of mitochondrial genes. These data provide essential information for understanding the transcription of mitochondrial genes in kenaf and can be used as a reference for other plants.

Sulfur-Resistant Ceria-Based Low-Temperature SCR Catalysts with the Non-bulk Electronic States of Ceria.

Although ceria-based catalysts serve as an appealing alternative to traditional V2O5-based catalysts for selective catalytic reduction (SCR) of NOx with NH3, the inevitable deactivation caused by SO2 at low temperatures severely hampers the ceria-based catalysts to efficiently control NOx emissions from SO2-containing stack gases. Here, we rationally design a strong sulfur-resistant ceria-based catalyst by tuning the electronic structures of ceria highly dispersed on acidic MoO3 surfaces. By using Ce L3-edge X-ray absorption near edge structure spectra in conjunction with various surface and bulk structural characterizations, we report that the sulfur resistance of the catalysts is closely associated with the electronic states of ceria, particularly expressed by the Ce3+/Ce4+ ratio related to the size of the ceria particles. As the Ce3+/Ce4+ ratio increases up to or over 50%, corresponding to CeO2/MoO3(x %, x ≤ 2.1) with the particle size of approximately 4 nm or less, the non-bulk electronic states of ceria appear, where the catalysts start to show strong sulfur resistance. This work could provide a new strategy for designing sulfur-resistant ceria-based SCR catalysts for controlling NOx emissions at low temperatures.

Stable single atomic silver wires assembling into a circuitry-connectable nanoarray.

Atomic metal wires have great promise for practical applications in devices due to their unique electronic properties. Unfortunately, such atomic wires are extremely unstable. Here we fabricate stable atomic silver wires (ASWs) with appreciably unoccupied states inside the parallel tunnels of α-MnO2 nanorods. These unoccupied Ag 4d orbitals strengthen the Ag-Ag bonds, greatly enhancing the stability of ASWs while the presence of delocalized 5s electrons makes the ASWs conducting. These stable ASWs form a coherently oriented three-dimensional wire array of over 10 nm in width and up to 1 µm in length allowing us to connect it to nano-electrodes. Current-voltage characteristics of ASWs show a temperature-dependent insulator-to-metal transition, suggesting that the atomic wires could be used as thermal electrical devices.

Single-atom catalysts reveal the dinuclear characteristic of active sites in NO selective reduction with NH3.

High-performance catalysts are extremely required for controlling NO emission via selective catalytic reduction (SCR), and to acquire a common structural feature of catalytic sites is one key prerequisite for developing such catalysts. We design a single-atom catalyst system and achieve a generic characteristic of highly active SCR catalytic sites. A single-atom Mo1/Fe2O3 catalyst is developed by anchoring single acidic Mo ions on (001) surfaces of reducible α-Fe2O3, and the individual Mo ion and one neighboring Fe ion are thus constructed as one dinuclear site. As the number of the dinuclear sites increases, SCR rates increase linearly but the apparent activation energy remains almost unchanged, evidencing the identity of the dinuclear active sites. We further design W1/Fe2O3 and Fe1/WO3 and find that tuning acid or/and redox properties of dinuclear sites can alter SCR rates. Therefore, this work provides a design strategy for developing improved SCR catalysts via optimizing acid-redox properties of dinuclear sites.

Single-ion copper doping greatly enhances catalytic activity of manganese oxides via electronic interactions.

Single-ion copper doping significantly improves the catalytic activity of α-MnO2 in CO oxidation, reducing the apparent activation energy to ∼0.3 eV via strong electronic interactions between the frontier orbitals of copper ions and manganese ions.

Rational design of alkali-resistant catalysts for selective NO reduction with NH3.

A rationale for designing selective NO reduction catalysts with strong alkali resistance was proposed, based on extensive studies of a variety of catalysts with common characteristics of separate catalytically active sites and alkali-trapping sites.

Self-Prevention of Well-Defined-Facet Fe2O3/MoO3 against Deposition of Ammonium Bisulfate in Low-Temperature NH3-SCR.

Low-temperature selective catalytic reduction of NO by NH3 (NH3-SCR) is a promising technology for controlling NO emission from various industrial boilers, but it remains challenging because unavoidable deposition of ammonium bisulfates (ABS) in the stack gases containing both SO2 and H2O inevitably results in deactivation of catalysts. Here we developed a stable low-temperature NH3-SCR catalyst by supporting Fe2O3 cubes on surfaces of MoO3 nanobelts with NH4+-intercalatable interlayers, which enables Fe2O3/MoO3 to spontaneously prevent ABS from depositing on the surfaces. Using in situ synchrotron X-ray diffraction, 1H magic angle spinning nuclear magnetic resonance, and temperature-programmed decomposition procedure, the results demonstrate that NH4+ of ABS was initially intercalated in the interlayers of MoO3, leading to a NH4+-HSO4- cation-anion separation by conquering their strong electrostatic interactions, and subsequently the separated NH4+ was consumed by taking part in low-temperature NH3-SCR. Meanwhile, the surface HSO4- separated from ABS oxidized the reduced catalyst during the NH3-SCR redox cycle, concomitant with release of SO2 gas, thereby resulting in decomposition of ABS. This work assists the design of stable low-temperature NH3-SCR catalysts with strong resistance against deposition of ABS.

Well-defined palladium-ceria interfacial electronic effects trigger CO oxidation.

Metal-support electronic interactions were investigated in CO oxidation by using a Pd/CeO2 model catalyst with well-defined interfaces, and electron transfer from Pd cubes to CeO2 nanorods through interfaces triggered CO oxidation at low temperature where standalone Pd and CeO2 are inert.

Activating Inert Alkali-Metal Ions by Electron Transfer from Manganese Oxide for Formaldehyde Abatement.

Alkali-metal ions often act as promoters rather than active components due to their stable outermost electronic configurations and their inert properties in heterogeneous catalysis. Herein, inert alkali-metal ions, such as K+ and Rb+ , are activated by electron transfer from a Hollandite-type manganese oxide (HMO) support for HCHO oxidation. Results from synchrotron X-ray diffraction, absorption, and photoelectron spectroscopies demonstrate that the electronic density of states of single alkali-metal adatoms is much higher than that of K+ or Rb+ , because electrons transfer from manganese to the alkali-metal adatoms through bridging lattice oxygen atoms. Electron transfer originates from the interactions of alkali metal d-sp frontier orbitals with lattice oxygen sp3 orbitals occupied by lone-pair electrons. Reaction kinetics data of HCHO oxidation reveal that the high electronic density of states of single alkali-metal adatoms is favorable for the activation of molecular oxygen. Mn L3 -edge and O K-edge soft-X-ray absorption spectra demonstrate that lattice oxygen partially gains electrons from the Mn eg orbitals, which leads to the upshift in energy of lattice oxygen orbitals. Therefore, the facile activation of molecular oxygen by the electron-abundant alkali-metal adatoms and active lattice oxygen are responsible for the high catalytic activity in complete oxidation of HCHO. This work could assist the design of efficient and cheap catalysts by tuning the electronic states of active components.

Sodium Rivals Silver as Single-Atom Active Centers for Catalyzing Abatement of Formaldehyde.

The development of efficient alkali-based catalysts for the abatement of formaldehyde (HCHO), a ubiquitous air pollutant, is economically desirable. Here we comparatively study the catalytic performance of two single-atom catalysts, Na1/HMO and Ag1/HMO (HMO = Hollandite manganese oxide), in the complete oxidation of HCHO at low temperatures, in which the products are only CO2 and H2O. These catalysts are synthesized by anchoring single sodium ions or silver atoms on HMO(001) surfaces. Synchrotron X-ray diffraction patterns with structural refinement together with transmission electron microscopy images demonstrate that single sodium ions on the HMO(001) surfaces of Na1/HMO have the same local structures as silver atoms of Ag1/HMO. Catalytic tests reveal that Na1/HMO has higher catalytic activity in low-temperature oxidation of HCHO than Ag1/HMO. X-ray photoelectron spectra and soft X-ray absorption spectra show that the surface lattice oxygen of Na1/HMO has a higher electronic density than that of Ag1/HMO, which is responsible for its higher catalytic efficiency in the oxidation of HCHO. This work could assist the rational design of cheap alkali metal catalysts for controlling the emissions of volatile organic compounds such as HCHO.

Single Silver Adatoms on Nanostructured Manganese Oxide Surfaces: Boosting Oxygen Activation for Benzene Abatement.

The involvement of a great amount of active oxygen species is a crucial requirement for catalytic oxidation of benzene, because complete mineralization of one benzene molecule needs 15 oxygen atoms. Here, we disperse single silver adatoms on nanostructured hollandite manganese oxide (HMO) surfaces by using a thermal diffusion method. The single-atom silver catalyst (Ag1/HMO) shows high catalytic activity in benzene oxidation, and 100% conversion is achieved at 220 °C at a high space velocity of 23 000 h-1. The Mars-van Krevelen mechanism is valid in our case as the reaction orders for both benzene and O2 approach one, according to reaction kinetics data. Data from H2 temperature-programmed reduction and O core-level X-ray photoelectron spectra (XPS) reveal that Ag1/HMO possesses a great amount of active surface lattice oxygen available for benzene oxidation. Valence-band XPS and density functional theoretical calculations demonstrate that the single Ag adatoms have the upshifted 4d orbitals, thus facilitating the activation of gaseous oxygen. Therefore, the excellent activation abilities of Ag1/HMO toward both surface lattice oxygen and gaseous oxygen account for its high catalytic activity in benzene oxidation. This work may assist with the rational design of efficient metal-oxide catalysts for the abatement of volatile organic compounds such as benzene.

Enhanced Performance of Ceria-Based NOx Reduction Catalysts by Optimal Support Effect.

CeO2-based catalysts have attracted widespread attention in environmental-protection applications, including selective catalytic reduction (SCR) of NO by NH3, and their catalytic performance is often intimately associated with the supports used. However, the issue of how to choose the supports of such catalysts still remains unresolved. Herein, we systematically study the support effect in SCR over CeO2-based catalysts by using three representative supports, Al2O3, TiO2, and hexagonal WO3 (HWO), with different acidic and redox properties. HWO, with both acidic and reducible properties, achieves an optimal support effect; that is, CeO2/HWO exhibits higher catalytic activity than CeO2 supported on acidic Al2O3 or reducible TiO2. Transmission electron microscopy and X-ray diffraction techniques demonstrate that acidic supports (HWO and Al2O3) are favorable for the dispersion of CeO2 on their surfaces. X-ray photoelectron spectroscopy coupled with theoretical calculations reveals that reducible supports (HWO and TiO2) facilitate strong electronic CeO2-support interactions. Hence, the excellent catalytic performance of CeO2/HWO is mainly ascribed to the high dispersion of CeO2 and the optimal electronic CeO2-support interactions. This work shows that abundant Brønsted acid sites and excellent redox ability of supports are two critical requirements for the design of efficient CeO2-based catalysts.

Self-Protection Mechanism of Hexagonal WO3-Based DeNOx Catalysts against Alkali Poisoning.

A good catalyst for efficiently controlling NOx emissions often demands strong resistance against alkali poisoning. Although the traditional ion-exchange model, based on acid-base reactions of alkalis with Brønsted acid sites, has been established over the past two decades, it is difficult to be used as a guideline to develop such an alkali-resistant catalyst. Here we establish a self-protection mechanism of deNOx catalysts against alkali poisoning by systematically studying the intrinsic nature of alkali resistance of V2O5/HWO (HWO = hexagonal WO3) that shows excellent resistance to alkali poisoning in selective catalytic reduction of NOx with NH3 (SCR). Synchrotron X-ray diffraction and absorption spectroscopies demonstrate that V2O5/HWO has spatially separated catalytically active sites (CASs) and alkali-trapping sites (ATSs). During the SCR process, ATSs spontaneously trap alkali ions such as K+, even if alkali ions initially block CASs, thus releasing CASs to realize the self-protection against alkali poisoning. X-ray photoelectron spectra coupled with theoretical calculations indicate that the electronic interaction between the alkali ions and ATSs with an energy saving is the driving force of the self-protection. This work provides a strategy to design alkali-resistant deNOx catalysts.