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Activated red mud (RM) has been proved to be a promising base material for the selective catalysis reduction (SCR) of NOx. The inherent low reducibility and acidity limited its low–temperature activity. In this work, molybdenum oxide, tungsten oxide, and cerium oxide were used to reconfigure the redox sites and acid sites of red mud based catalyst. When activated red mud was reconfigured by cerium-tungsten oxide (Ce–W@RM), the NOx conversion kept above 90% at 219–480 °C. The existence of Ce3+/Ce4+ redox electron pairs provided more surface adsorbed oxygen (Oα) and served as a redox cycle. Positive interactions between Ce, W species and Fe oxide in red mud occurred, which led to the formation of unsaturated chemical bond and promoted the activation of adsorbed NH3 species. WO3 and Ce2(WO4)3 (formed by solid–state reaction between Ce and W species) could provide more Bronsted acid sites (W–O modes of WO3, W O or W–O–W modes of Ce2(WO4)3). CeO2 species could provide more Lewis acid sites. The Langmuir–Hinshelwood (L-H) routes and Eley-Rideal (E-R) routes occurred in the low-temperature SCR reaction on the Ce–W@RM surface. NH4+ species on Bronsted acid sites, NH3 species on Lewis acid sites, bidentate nitrate and bridging nitrate species were key active intermediates species.

Here, we report a Ru/TS-1 catalyst for selective hydrogenolysis of guaiacol to benzene in the aqueous phase at conditions of 240 °C and 2 bar H2, achieving a benzene yield of 86% with a hydrogenolysis rate of 103.1 mmol g−1 h−1. It was found that Silicalite-1 (MFI type) with suitable pore sizes supported Ru nanoparticles (NPs) favored for hydrogenolysis of guaiacol, whereas de-aluminated Ru/HBEA, Ru/HY and Ru/MWW (without acidic sites) accelerated the parallel reactions of hydrogenation of aromatics. In addition, Ru NPs located at the orifice of Silicalite-1 was proved to be more electron-deficient and active than Ru NPs on the outer surface, as evidenced by CO-IR characterization and activity tests on Ru/Silicalite-1 (with and without templates). Moreover, Bronsted acid sites (BAS) on Ru/MFI highly promoted the hydrogenation rates of aromatics, while Lewis acid sites (LAS) on Ru/TS-1 and Ru/MFI led to a linear increase of guaiacol hydrogenolysis rate to benzene, probably due to the enhanced absorbance capability of guaiacol and phenol on the LAS of MFI. Thus, pore structure properties of MFI coupled with abundant LAS (TS-1) as well as Ru NPs on the orifice of pores of TS-1 construct a promising catalyst for achieving efficient aromatic hydrocarbons from selective hydrogenolysis of lignin.

The CeO2, Ce-Nb-Ox and Nb2O5 catalysts were synthesized by citric acid method to investigate the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH3. The catalytic activity measurements indicate that the mixed oxide Ce-Nb-Ox presents a higher SCR activity than the single oxide CeO2 or Nb2O5 catalyst. In addition, the Ce-Nb-Ox catalyst shows a high resistance towards H2O and SO2 at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H2 results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH3 results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce-Nb-Ox catalyst possessing a high content of Lewis and Bronsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce-Nb-Ox catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH3 on Lewis acid sites and NH4+ on Bronsted acid sites can react with NO species, and adsorbed NO and NO2 species can both be reduced by NH3. In the SCR process, O2 as an important role primarily acts as the accelerant to improve the redox and acid cycles. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.

HZSM-5 zeolites with Si/Al ratios of 20, 35, 50 and 65 were prepared by the directing crystallization process of silicalite-1 seeds. The influence of Si/Al ratios on the production of benzene, toluene, xylene and naphthalene (BTXN) originated from asphaltenes catalytic pyrolysis was explored by adopting Py-GC/MS. Modified Z5-50 zeolites were prepared by various metal ions (Ni2+, Mo6+, Fe3+, and Co2+) with different loading rates (3 % (mass), 5 % (mass), 7 % (mass), and 9 % (mass)) and the physical and chemical properties of these zeolites were characterized by XRD, SEM, ICP-OES, XPS, NH3-TPD, FTIR, Py-IR and N2 adsorption-desorption isotherm. In addition, they were employed to catalyze the conversion of asphaltenes pyrolysis production to BTXN using Py-GC/MS. Results show that the highest relative content of aromatics has been obtained over HZSM-5 with Si/Al ratio of 50 (Z5-50), reaching 61.87%. Besides, the loading of Ni, Mo, Fe, and Co on Z5-50 leads to an increase of acid strength and provides new active sites. The relative content of BTXN increases by 3.17% over 3Ni-Z5, which may be ascribed to that Ni promoted the conversion of polycyclic aromatic hydrocarbons (PAHs) to monocyclic aromatics due to the cracking of aliphatic side chains of PAHs and the decrease of phenolic activation energy. While under the catalysis of 5Mo-Z5, the relative content of aromatics and BTXN augmented by 5.75% and 4.02%, respectively. In addition, the highest relative content of aromatics reaches 70.09% when the loading rate of Fe was 7 % (mass), and the relative content of BTXN increases from 25.87% to 29.42%. The results demonstrate that the active sites provided by different metal species expressed diverse effects on BTXN. Although the Bronsted/Lewis acid ratios of HZSM-5 modified by metal decreased, the acid strength and the relative content of BTXN both increased, which illustrated that there is a synergistic catalysis with the Bronsted acid sites and Lewis acid sites provided by metal species. In general, the performance of the catalyst is affected by the pore structure, acidity and metal active sites. Moreover, the possible formation mechanism of BTXN derived from asphaltenes catalytic pyrolysis was proposed on the basis of structural features and catalytic performances of a series of zeolites.

The classical Hantzsch reaction is a simple and utmost efficient protocol for the synthesis of biologically and pharmacologically important 1,4-dihydropyridine derivatives. The present study deals with the utilization of modified heteropoly acid (HPA) catalysts (5 wt% WOx-FeP and 5 wt% MoOx-FeP) in the synthesis of novel Hantzsch 1,4-dihydropyridines, which contains diphenylsulfone moiety via one-pot synthesis strategy under ultrasound irradiation. The developed protocol is simple and green procedure for the synthesis of 1,4-dihydropyridines and is applicable to synthesize different 1,4-dihydropyridine derivatives. The synthesized HPA catalysts offered a sustainable methodology to produce excellent products yields (88–92%) of 1,4-dihydropyridine derivatives. The catalysts were characterized by XRD, Raman, FT-IR, DRUV-vis, XPS, H2-TPR, N2-physisorption and acidity measurements. The HPA supported iron phosphate nanotubes (FeP) catalysts offered enhanced the catalytic performance through the improved Lewis acid site density, redox properties and surface area, compared to the parent phosphomolybdic and phosphotungstic acids. Moreover, the synthesized catalysts can be easily separated from reaction system and reused for six times efficiently without significant loss of activity.

To modulate the acid properties of Sn-SBA-15-PrSO3H materials, the synthesis of heterogeneous Sn-SBA-15 catalysts modified with –PrSO3H groups was performed using the sol-gel method. This method enabled the integration of Sn in the structure of SBA-15, which was achieved by replacing Si+4 with Sn+4 ions, or by generating small amounts of SnO2 nanoparticles in octahedral coordination on the surface of the material. Incorporation of the –PrSO3H groups into the Sn-SBA-15 catalysts results in a significant increase in Bronsted and, to a lesser extent, Lewis acid sites. The relative concentration of Bronsted to Lewis acid sites was approximately 4:1. This improvement in the acid properties of the catalysts, led to an increase in the reaction rate for the esterification of oleic acid with methanol, achieving conversions that reach 96% at 100 °C after 2 h of reaction. The most favorable synthesis conditions were observed when the highest concentration of acid was used in the synthesis gel (1.1 M). This is due to the higher production of Sn+4 tetrahedral species in the SBA-15 structure and better integration of the -PrSO3H groups into the materials, which are mainly related to Bronsted acid sites. Finally, a linear relationship was established between the concentration of Bronsted acid sites in the catalyst and the catalytic activity for the oleic acid esterification and a second-order reversible model satisfactorily reproduces the experimental kinetic data.

The synthesis of homolimonenol by Prins condensation of limonene and paraformaldehyde over heterogeneous tin-based catalysts is reported for the first time. The tin supported MCM-41, SBA-15, and KIT-6 materials were prepared by incipient wetness impregnation method, using SnCl2·2H2O as a tin precursor. The synthesized catalysts were characterized by N2-physisorption, X-ray diffraction (XRD), diffuse reflectance-infrared Fourier transform spectroscopy (DRIFTS), pyridine adsorption (Py-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and chemical analysis. Sn4+ species were identified on the surface of the catalysts, and the materials showed mainly Lewis acid sites, which are responsible for the activity in the Prins reaction. Production of homolimonenol was confirmed by GC-MS and NMR analysis. Among the evaluated catalysts, the best conversion (26%), selectivity (90%) and TOF (12.7 h−1) were obtained over Sn-SBA-15, in the presence of ethyl acetate; Sn-SBA-15 catalyst was reused five times without loss of activity. The reaction was scaled up from 2 to 200 mL glass reactor with a local orange oil (93% wt/wt limonene) as a substrate, obtaining a 30% conversion of limonene and a 93% selectivity to homolimonenol.

Ambient electrochemical nitrogen fixation is a promising and environmentally benign route for producing sustainable ammonia, but has been limited by the poor performance of existing catalysts that ...

The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during combustion. In this work, a series of spherical sulfated zirconia catalysts were prepared by a one-pot hydrothermal method assisted with surfactant cetyltrimethylammonium bromide (CTAB). The prepared sulfated zirconia catalysts were used to catalyze PODEn synthesis from methanol and formaldehyde solution. Various characterization (XRD, BET, SEM, TGA, NH3-TPD, FTIR, and Py-IR) were employed to elaborate the structure-activity relationship of the studied catalytic system. The results demonstrated that S/Zr molar ratio in precursor solution played an effective role on catalyst morphology and acidic properties, where the weak Bronsted acid sites and strong Lewis acid sites were favorable to the conversion of methanol and formation of long-chain PODEn, respectively. The reaction parameters such as catalyst amount, molar ratio of FA/MeOH, reaction time, temperature and pressure were optimized. The speculated reaction pathway for PODEn synthesis was proposed based on the synergy of Bronsted and Lewis acid sites, which suggested that Bronsted and Lewis acid sites might be advantageous to the activation of polyoxymethylene hemiformals [CH3(OCH2)nOH] and methylene glycol (HOCH2OH), respectively.

Lewis base-catalyzed annulations of allenoates have been one of the most powerful synthetic strategies for the synthesis of various valuable cycles, especially in the preparation of biologically active natural products and pharmaceuticals. Generally, the effective Lewis bases mainly include tertiary phosphine, NHC and tertiary amine catalysts, among those catalysis, tertiary amine Lewis bases have proven to be effective catalysts for a range of synthetic transformations. In the past decades, tremendous progress involving tertiary amines-promoted cycloaddition of allenoates has been made in the chemoselective construction of valuable motifs. This review describes a comprehensive and updated summary of tertiary amine Lewis base-promoted annulation reactions of allenoates. Diverse reactivities, chemoselectivties and detailed reaction mechanisms will be highlighted in this review.

A series of bifunctional ZnCe@SBA-15 catalysts with different Zn/Ce ratios were prepared by a solid-state grinding strategy and used in the conversion of ethanol to 1,3-butadiene (ETB). For the supported metal oxides, ZnO serves as the active sites for the dehydrogenation of ethanol, and CeO2 promotes the aldol-condensation reaction. Based on the results of Py-FTIR and NH3-TPD, it suggests that the yield of 1,3-butadiene is positively correlated with the number of weak Lewis acid sites on the catalyst surface, given their benefit for aldol-condensation reactions. The catalyst with an optimal Zn/Ce ratio of about 1:5 has the highest concentration of weak Lewis acid. Coupling with the ZnO sites, it contributes to a 98.4% conversion of ethanol and a 45.2% selective of 1,3-butadiene under relatively mild reaction conditions (375 °C, 101.325 kPa, and 0.54 h−1).

Reduction of overstable dinitrogen (N2) is hampered by kinetically complex and challenging multi-electron reactions. One grand challenge is to develop efficient and economical catalysts for photocatalytic nitrogen fixation (PNF) under ambient conditions. Herein, we report that the intrinsic Bronsted-Lewis dual acid sites (F-H-TiO2) on the surface of F-modified TiO2 nanosheets can significantly lower the energy barrier generated by *N2H (the rate-determining step) to efficiently produce NH3. The surface Lewis acid (the ≡Ti−F groups) allows strong chemisorption and activation of molecule N2, and the surface Bronsted acid (the vicinal hanging OH groups) can further improve N2 adsorption energy and provide in-situ protons to accelerate the photocatalytic proton-coupled electron transfer (pPCET) process. The synergy of Bronsted-Lewis dual acid sites provides significantly enhanced PNF performance, exhibiting NH3 production rate up to 308.6 μmol g–1 h–1 with the corresponding apparent quantum efficiency (AQE) of 0.35% at 400 nm. Therefore, it provides a promising and facile strategy to achieve high-efficiency PNF on excellent semiconductor substrates by modifying the TiO2 surface with light elements.

A novel solid Bronsted-Lewis acid catalyst La-PW-SiO2/SWCNTs was synthesized from the synergistic modification of H3PW12O40 (HPW) by single-walled carbon nanotubes functionalized with sidewall hydroxyl groups (SWCNTs–OH) and La3+ via sol-gel method. The freshly prepared catalyst was characterized by several methods, and the catalytic activity and stability of it were studied from the esterification of oleic acid and methanol. Results showed that the highest conversion of oleic acid was 93.1 wt% and maintained as high as 88.7 wt% after six cycles of La-PW-SiO2/SWCNTs. The high catalytic activity and stability of La-PW-SiO2/SWCNTs can be attributed to the strong electron withdrawing effect of La3+ on π bond of SWCNTs, because it can facilitate the formation of a large number of strong Lewis acid sites. Therefore, the reduction of catalytic activity of a solid acid catalyst due to the fact that hydration reaction of its Bronsted acid sites can be effectively reduced. La-PW-SiO2/SWCNTs can be an efficient and economical catalyst, because it shows good catalytic activity and stability.

Understanding the complete reaction network and mechanism of methanol-to-hydrocarbons remains a key challenge in the field of zeolite catalysis and C1 chemistry. Inspired by the identification of the reactive surface methoxy species on solid acids, several direct mechanisms associated with the formation of the first C-C bond in methanol conversion have been recently disclosed. Identifying the stepwise involvement of the initial intermediates containing the first C-C bond in the whole reaction process of methanol-to-hydrocarbons conversion becomes possible and attractive for the further development of this important reaction. Herein, several initial unsaturated aldehydes/ketones containing the C-C bond are identified via complementary spectroscopic techniques. With the combination of kinetic and spectroscopic analyses, a complete roadmap of the zeolite-catalyzed methanol-to-hydrocarbons conversion from the initial C-C bonds to the hydrocarbon pool species via the oxygen-containing unsaturated intermediates is clearly illustrated. With the participation of both Bronsted and Lewis acid sites in H-ZSM-5 zeolite, an initial aldol-cycle is proposed, which can be closely connected to the well-known dual-cycle mechanism in the methanol-to-hydrocarbons conversion.

Photocatalytic upgrading of renewable biomass is a promising way to relieve energy crisis and environmental pollution. However, low photocatalytic efficiency and uncontrollable selectivity still limit its development. Herein, ultrathin SnNb2O6 nanosheets with high dispersed Pt nanoparticles (Pt/SN) were successfully developed as an efficient photocatalyst for the precise hydrogenation of furfural (FUR) to furfuryl alcohol (FOL) under visible light irradiation and exhibited the high conversion of FUR (99.9%) with the high selectivity for FOL (99.9%). It was revealed that SN with only 4.1 nm thickness possess good separation ability of photo-generated carriers and abundant surface Lewis acid sites (Nb5+) which would selectively chemisorb and activate FUR molecules via the Nb···O = C coordination. Meanwhile, Pt nanoparticles would gather photo-generated electrons for greatly promoting the generation of active H species to support the hydrogenation of FUR to FOL. The synergistic effects between SnNb2O6 nanosheets and Pt nanoparticles remarkably facilitate the photocatalytic performance for hydrogenation. This work not only confirms the great potential of ultrathin nanosheet photocatalyst with functional metal sites for precise upgrading of biomass but also provides an in-depth view to understand the surface/interface interaction between reactant molecules and surface sites of a photocatalyst.

The shale gas revolution and the carbon-neutrality goal are motivating the landscape toward the synthesis of value-added chemicals or fuels from underutilized ethane with the assistance of greenhouse gas CO2. Combining ethane aromatization with CO2 reduction offers an opportunity to directly produce liquid products for facile separation, storage, and transportation. In the present work, Fe/ZSM-5 catalysts showed promise in the simultaneous CO2 reduction and ethane aromatization at atmospheric pressure and 873 K. The catalysts were further investigated using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements under in-situ conditions, indicating that most of Fe species existed in the form of Fe oxides and a portion of Fe was incorporated into the ZSM-5 framework generating Lewis acid sites. Both types of Fe species remained almost unchanged under reaction conditions, contributing to an enhanced aromatization activity of Fe/ZSM-5. The effects of CO2 and steam on the acid sites and in turn aromatization activity were also investigated by transient studies, which exhibited a reversible modification behavior. Moreover, CO2 was identified to be critical to enhance coke resistance and in turn catalyst stability. This work highlights the feasibility of using CO2 to assist the upgrading of abundant ethane from shale gas to aromatics over non-precious Fe-based zeolite catalysts.

A Lewis acid-catalyzed [4 + 2] cycloaddition of 3-alkyl-2-vinylindoles with β,γ-unsaturated α-ketoesters has been established in the presence of Sc(OTf)3, which afforded a series of indole-containing pyran derivatives in generally good yields (up to 90% yield) with excellent diastereoselectivities (up to >95:5 dr) under mild conditions. This approach not only enriches the chemistry of 3-alkyl-2-vinylindoles, but also has provided an atom-economic method for the synthesis of indole-containing pyran derivatives with potential bioactivity.

In this paper, sulfated ZrO2 were synthesized via precipitation and impregnation method, and the promoting effects of support sulfation on selective catalytic reduction (SCR) performance of CeO2/ZrO2 catalysts were investigated. The results revealed that sulfated ZrO2 could significantly enhance the SCR activity of CeO2/ZrO2 catalysts in a wide temperature range. Especially when S/Zr molar ratio was 0.1, CeO2/ZrO2-0.1S catalyst exhibited a large operating temperature window of 251 ∼ 500 °C and its N2 selectivity was 100 % in the temperature range of 150 ∼ 500 °C. Moreover, CeO2/ZrO2-0.1S catalyst possessed a superior low-temperature activity over 0.1S-CeO2/ZrO2 catalyst. After exposing to 100 ppm SO2 for 15 h, a high NO conversion efficiency of CeO2/ZrO2-0.1S catalyst (90.7 %) could still be reached. The characterization results indicated that ZrO2 treated with a proper dosage of sulfate acid was beneficial to enlarge the specific surface area greatly. Sulfated ZrO2 was also in favor of promoting the transformation of CeO2 from crystalline state to highly-dispersed amorphous state, and inhibiting the transformation of ZrO2 from tetragonal to monoclinic phase. It could also enhance the total surface acidity greatly with an increase in both Bronsted acid sites and Lewis acid sites, thus significantly improving NH3 adsorption on catalyst surface. Besides, the promoting effect of support sulfation on SCR performance of CeO2/ZrO2 catalysts was also related with the enhanced redox property, higher Ce3+/(Ce3++Ce4+) ratio and abundant surface chemisorbed labile oxygen. The in-situ DRIFTS results implied that nitrate species coordinated on the surface of CeO2/ZrO2-0.1S catalyst could participate in the Selective catalytic reduction with ammonia (NH3-SCR) reactions at either medium or high temperature, suggesting that both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms might be followed in SCR reactions.

Surface interface regulation is an important research content in the field of heterogeneous catalysis. To improve the interface interaction between the active component and matrix, tremendous efforts have been dedicated to tailoring the morphology, size, and structure of composite catalysts. In this work, we report a confinement strategy to synthesize a series of core-shell catalysts loaded with metal oxides on titania nanotubes (TNTs), which were applied to the selective catalytic reduction of NOx with ammonia. Interestingly, the core-shell catalyst with confinement of TNTs exhibited the remarkable activity at low temperature region, N2 selectivity and sulfur tolerance. Benefiting from the superior interfacial confinement characteristic of TNTs and Fe2O3, strong component interactions, the surface acid sites and strong oxidizability of MnOx were properly regulated, thus obtained the outstanding activity, N2 selectivity and provide chemical protection to effectively prevent SO2 poisoning. As far as the reaction mechanism, we found that the adsorption and reactivity of Lewis acid sites were the dominant factors affecting the activity in the NH3-SCR process by in situ DRIFT spectra. In general, our work provides an innovative strategy for constructing an TNTs-enwrapped nanocomposite with nano-confinement and core-shell structure to improve the low temperature SCR process.

NOx and toluene have been identified as the dominant air pollutants in solid wasted combustion, and it is of great importance to remove these two pollutants simultaneously. Here, we found that Mn/CeO2 and Mn/TiO2 exhibited a bifunctional property in both NO reduction and toluene oxidation, and both of which could achieve 80% of conversion rate in NO reduction and toluene oxidation processes. However, the activity of both Mn/CeO2 and Mn/TiO2 decreased in simultaneous removal of NOx and toluene compared with separate NOx reduction and toluene oxidation. This indicates that there is a mutual inhibition between NOx reduction and toluene oxidation in simultaneous removal process over Mn-based catalysts, attributing to the competitive adsorption and utilization of active oxygen. In detail, the adsorption of toluene occupied the Lewis acid sites and restrained the NH3 adsorption. Meanwhile, the competitive utilization of active oxygen by NH3/NOx inhibited toluene oxidation to CO2 by active oxygen species as the reaction between NH3/NOx and active oxygen species would occur more easily.

An ultra-active metal-free ORR electrocatalyst (F–N-AC-1000) was developed by fluorine doped N-based activated carbon. The as-prepared F–N-AC-1000 exhibited half-wave potentials of 0.89 V and 0.75 V (vs. RHE) in alkaline and acidic electrolytes, respectively, which are both among the most active metal-free ORR catalysts reported in the literature. F–N-AC-1000 also showed much higher methanol tolerance and stability than the commercial Pt/C catalyst. Experimental and theoretical calculation results demonstrated a novel viewpoint on synergistic effect that the superior ORR performance could be mainly ascribed to the incorporation of fluorine atom into the pyridinic-N configuration, and the charge and spin densities of the adjacent C atoms (Lewis base site) were significantly improved in comparison with the absolute pyridine structure. High ORR performance was attributed to the enhanced Lewis base site rather than the increase of the total content of active sites at the location of the doped fluorine and nitrogen atoms. The hierarchical pore structure with large specific surface area could supply more available active sites and provide fast transport channel for electrons and products. This study will provide useful guidance for the design of superior metal-free ORR catalysts, promoting the application of metal-free carbon-based catalysts in batteries or fuel cells.

Converting carbohydrates into lactic acid has attracted increasing attention due to the wide applications of lactic acid. However, the current methods of thermochemical conversion are commonly suffering from limited selectivity or harsh conditions. Herein, a light-driven system of highly selective conversion of glucose into lactic acid at low temperatures was developed. By constructing a hybrid multifunctional catalyst multi-walled carbon nanotubes/layered double hydroxides composites (CNT/LDHs), the highest lactic acid yield of 88.6 % with 90.0 % selectivity was achieved. The outperformance of CNT/LDHs for lactic acid production from glucose is attributed to the following factors: (i) CNT generate strong heating center under irradiation, providing heat for converting glucose into lactic acid; (ii) LDHs catalyze glucose isomerization, in which the photoinduced OVs (Lewis acid) in LDHs under irradiation further improve the catalytic activity; (iii) In heterogeneous-homogeneous synergistically catalytic system (LDHs-OH-), OH- ions are concentrated in LDHs, forming strong base sites to catalyze subsequent cascade reactions.

A high surface acidic ZrO2 nanoparticle was prepared using glucose as a non-toxic reducing agent. Palladium (Pd) nanoparticles in the range of 1–2 nm are grafted in in-situ as well as ex-situ via urea deposition over pre-synthesized ZrO2 nanoparticles. Both methods are found to be useful for the one-pot transformation of glucose to HMF, and their catalytic activities towards selective production of HMF are found to be strongly dependent on the particle size and nature of acidic sites. A linear-type activity trend is observed with Pd loading in reference to the HMF selectivity and presents the best catalytic performance. The activation energy and turnover frequency (TOF) of the 1–2 nm NP catalyst are further calculated to be 44.1 kJ mol−1 and 6.011 molHMF·molPd−1·h−1, respectively. Characterization of the spent catalysts indicates that smaller-sized NPs face severe agglomeration, resulting in poor stability and activity. Hence, the high catalytic performance can be attributed to the balance between Bronsted and Lewis acid sites, in combination with Pd species intrinsic activity. Due to their improved activity and stability, 2Pd–ZrO2in-situ exhibits 55% glucose conversion with 74.0% of HMF selectivity after 3h of reaction at 160 °C.

A highly stable Pd-loaded N-doped carbon catalyst (ACNpd) for phenol hydrogenation was prepared from chitosan by hydrothermal carbonization. ACNpd does not require a reduction step before catalytic use due to the Pd in the as-prepared catalyst mainly exists in the form of Pd0 (80%). The carbon support involves N-containing groups such as pyridinic nitrogen and pyrrolic nitrogen, which could provide basic sites to adsorb phenol effectively. The as-fabricated ACNpd shows high catalytic performance with turnover frequency (TOF) of 29.34 h−1. Accordingly, a phenol conversion of 100% and a cyclohexanone selectivity of 99.1% are achieved in 5 h at 100 °C and 1 MPa H2. This outstanding performance is attributed to the synergetic effects of the Pd particles, the N-functional groups, and the Lewis acid sites on the support. The carbon support presents intrinsic Lewis acid sites due to its electrophilicity, and Pd doping further increases the strength of such acid sites as it causes electron-deficient structural features. Moreover, the Lewis acid sites inhibit the over-hydrogenation from cyclohexanone to cyclohexanol. This study provides new insights into the application of functional biomass-based carbon materials as catalyst supports.

The design and fabrication of efficient catalysts for ammonium perchlorate (AP) decomposition is crucial for the performance of composite solid propellants. Herein, a novel hierarchical structure material of Cu-WO3 nanowire arrays on a nanoflower flake (Cu-WO3 NANF) was synthesized by a facile hydrothermal reaction. The negatively charged (001) polar facets of hexagonal WO3 and the action of Cu2+ induced growth were two important factors for the formation of hierarchical structures. The Cu-WO3 NANF exhibited remarkable catalytic activity for the thermal decomposition of AP. The temperature and activation energy of high temperature AP decomposition were significantly decreased to 378.3 °C and 147.01 kJ mol−1, respectively, which are attributed to the more oxygen vacancies and lower band gap energy of the Cu-WO3 NANF. Thus, it was excited at a lower heat to produce activated species. Under the strong adsorption of Cu-WO3 NANF surface Lewis acid, the activated species can react with NH3 quickly and deeply to produce N2, N2O, NO2 and NO gases, accompanied by a heat release of up to 1118 J g−1. The proposed catalytic mechanism was further corroborated by the in situ TG-MS result. This facile strategy provided a new idea for the design of hierarchical catalysts, and our research opened up a new field for WO3 applications.

The higher–order cycloaddition reactions of tropone with nucleophilic ethylenes, in the absence and presence of Lewis acid (LA) catalysts, have been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) and B3LYP-D3BJ/6-311G(d,p) computational levels. The strong electrophilic character of tropone, enhanced by the presence of LAs, allows its participation in polar cycloaddition reactions of reverse electron density flux (REDF) towards nucleophilic ethylenes. Analysis of the Parr functions indicates that the C2 and the C4 position of tropone are the most electrophilic centers. These polar higher–order cycloaddition reactions take place via a non-concerted two-stage one-step or a two-step mechanism, yielding only one cycloadduct via a total regio and pseudocyclic selectivity. The present MEDT study allows establishing that these higher–order cycloaddition reactions are kinetically controlled by nucleophilic/electrophilic interactions taking place at the polar transition state structures (TSs). LAs not only accelerate the reaction and make it completely regioselective but also determine the pseudocyclic selectivity yielding exclusively [4+2] or [8+2] cycloadducts, which depends on a series of weak attractive/repulsive intramolecular electronic interactions present at the corresponding diastereoisomeric TSs.

We present a phosphonium-containing catalyst generated in situ from phosphine and tert-butyl acrylate that serves as an unusual Lewis base catalyst. It was applied for the promotion of a remote 1,6-cyanation reaction of p-quinone methides and fuchsones employing trimethylsilyl cyanide as the cyanide source. A diverse range of α-diaryl and α-triaryl acetonitriles was obtained in high yields under mild reaction conditions with low catalyst loading (5 mol%). The practicality and utility of this protocol were demonstrated via the gram-scale preparation and facile elaboration of products. Mechanistic investigations (in situ NMR and ESI-MS analysis) were employed to characterize the active zwitterionic phosphonium intermediate, which was the “true” active catalyst.

Modulation of surface acid sites (SAS) can effectively enhance the efficiency of reactive oxygen species (ROS) production in recent. However, the role of SAS has been neglected for photo-reduction reactions. Here, we report a Lewis acid site (L-acid) rich TiO2 prepared by synergistic effect of ethanol and halogen ions. The formation of L-acid improves the adsorption and mobility of O2, which facilitates to be reduced into superoxide radical (·O2-). L-acid may lift the population of photogenerated electrons (e-), which is concluded from the presence of ·CH3 signal in DMPO-·O2- ESR of only L-acid rich TiO2. In addition, L-acid enhances the migration of photogenerated holes (h+) to the surface of catalyst, which induces a continuous photo-oxidation reaction of H2O or -OH. Therefore, L-acid simultaneously enhances the photo-redox ROS generation reaction, resulting in higher photocatalytic activity. This work illustrates a dual function of L-acid and provides a useful strategy for improving the photocarriers separation and surface reaction efficiency.

In the present study, Ru modified hierarchical zeolites xRu-MZSM were developed for cellulose fast pyrolysis. Comprehensive catalyst characterizations including XRD, XPS, N2 adsorption-desorption, Py-IR and so on, were performed to unveil the essential structural properties. The chemical modification and Ru decoration remarkably regulated the distribution of Bronsted/Lewis acid sites. The presence of RuOx species would supply abundant strong Lewis acid sites for participating catalytic cracking, dehydration, decarbonylation, decarboxylation, cyclization, aromatization, etc., in cooperation with Bronsted acid sites. In-situ generated active Ru0 centers during cellulose pyrolysis might facilitate the proceeding of deoxygenation, hydride transfer, and dehydrogenation. Among the as-prepared catalysts screened, 2Ru-MZSM was much more efficient in aromatics production from cellulose fast pyrolysis compared to parent ZSM, wherein the total aromatics yield achieved 16.8% at temperature of 650 °C and heating rate of 10 °C/ms with corresponding E value as low as 23.40 kJ/mol. Also, plausible reaction mechanism for xRu-MZSM involved cellulose fast pyrolysis was proposed in detail.

Herein we report a diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones through base-promoted (3 + 2) cycloadditions. Importantly, the catalysts are found to have full control over the configuration of the stereocenters. When a Lewis base (PCy3) is used as a catalyst, good yields and excellent diastereoselectivities are obtained, regardless of the properties of the substituents, whereas spiro[indoline-3,2′-pyrrolidin]-2-ones of a different diastereoisomer are produced in good yields when a Bronsted base (K2CO3) is used. ESI-MS experiments proved the existence of key zwitterionic intermediates.

Al-Incorporated sulfated zirconia with improved and stabilized surface sulfur species was synthesized via the co-precipitation method and used as an effective catalyst to remove trace olefins from aromatics in a fixed-bed reactor. The textural and chemical properties of various catalysts were characterized by XRD, 27Al MAS NMR, N2 adsorption, EA, XPS, H2-TPR, FT-IR, and pyridine-infrared (IR) spectroscopy techniques to elucidate the Al promoting effect on acid centres and catalytic performance. The results demonstrated that incorporating Al into zirconia could effectively stabilize the tetragonal zirconia with small grain size and improve surface sulfur species, thereby balancing the distribution of Bronsted and Lewis acid sites. Consequently, sulfated zirconia incorporating Al at the level of Al/Zr < 7.5 mol% exhibited more outstanding catalytic activity and stability under a long reaction time compared with conventional sulfated zirconia. Notably, superior reusability with a negligible drop in olefins conversion over five reaction cycles was obtained in the presence of the Al2.50-SZ. The alkylation reaction process of olefins with aromatics was further investigated by the GC-MS technique when Alx-SZ was used as the catalyst.

The influence of sodium and lithium content in the metasilicate crystal structure ( S i O 3 2 − ) is herein analyzed concerning the heterogeneous transesterification reaction for biodiesel production. Na2SiO3 and Li2SiO3 were characterized structurally and microstructurally. The catalyst content was evaluated between 1 and 5 wt %, where the maximum FAME conversions (∼99%) were obtained using 3 wt % of Na2SiO3 during 1 h at 65 °C. After some cyclic experiments, it was determined that Na2SiO3 possesses a better stability and consequently reutilization capacity than Li2SiO3 in terms of its FAME conversion. DFT calculations were then used to analyze these experimental differences, revealing significant differences between these two catalysts in terms of energy, geometrical configuration, and electronic structure. It was found that three active sites are required on both catalytic surfaces to overcome the methanol deprotonation, which is herein suggested as the rate-controlling step of the entire transesterification mechanism. In one site, the oxygen atom of methanol approaches, while Lewis acid and Bronsted base sites are needed for the methoxide anion stabilization and proton stabilization, respectively.

Catalytic activity of TiO2, 2%Re–TiO2 and 10%Re–TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method, for the first time to the best of our knowledge, and characterized by XPS, SEM-EDX, DRIFTS, DR UV-vis, Raman, N2 adsorption/desorption isotherms, TGA and XRD. Further, the surface acidity was probed by NH3-TPD and pyridine-FT-IR where it was observed that increasing the amount of rhenium doped into TiO2 led to an increase in the total number of acid sites (Lewis + Brønsted) but with an overall lower strength. The presence of both Brønsted and Lewis acid sites led to the hypothesis that these materials may be well suited for conversion of carbohydrates into levulinic acid. Indeed a levulinic acid yield of 57% was reached over 10%Re–TiO2 for a low mass ratio catalyst to glucose (1 : 5). Moreover, the 10%Re–TiO2 catalyst was reused in the conversion of glucose for four catalytic cycles without a significant loss of the catalytic activity.

The development of efficient and sustainable strategies that evades the utilization of petroleum reserves is highly challenging yet inevitable today. In this regard, the conversion of pine tree-derived β-pinene to highly recognized nopol is particularly attractive owing to its widespread applications. Herein, we describe an approach that enables the selective synthesis of nopol with extraordinarily activity of MIL-101(Cr). This remarkable activity of MIL-101(Cr) attributed to its high specific surface area (SSA), accessible active sites in the mesopore architecture and unsaturated Cr3+ Lewis acid sites. We have established a good correlation between the superior catalytic performance and textural properties of the materials, which can be tuned by using different mineralizing agents. To realize the unprecedented catalytic activity, the influence of reaction parameters, solvent properties, and mineralizing agents have been investigated systematically. The MIL-101(AA) (AA-Acetic acid) exemplified the highest catalytic activity, which is superior to most of the reported materials for this transformation to date. The results of catalyst recycle and hot filtration experiments have emphasized that the catalyst is resistant towards leaching of active sites and retained its original catalytic activity beyond four recycles. An Eley Rideal based model was used to study the reaction kinetics and establish a plausible reaction mechanism. The activation energy of the reaction was found to be 102 kJ mol-1 and the enthalpy of formaldehyde adsorption is -86.88 kJ mol-1.This approach opens up new avenues for the valorization of biomass-based molecules into useful chemicals.

Although the selective hydrogenation of α,β-unsaturated aldehyde to unsaturated alcohol (UOL) is an extremely important transformation, it is still a great challenge to achieve high selectivity to UOL due to thermodynamic favoring of the C C hydrogenation over the C O hydrogenation. Herein, we report that iridium nanoclusters (Ir NCs) confined within hollow MIL-101(Fe) expresses satisfied reaction activity (93.9%) and high selectivity (96.2%) for the hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) under 1 bar H2 atmosphere and room temperature. The unique hollow structure of MIL-101(Fe) benefits for the fast transport of reactant, ensuring the comparable reaction activity and better recyclability of Ir@MIL-101(Fe) than the counterparts which Ir NCs were on the surface of MIL-101(Fe). Furthermore, The X-ray photoelectron spectroscopy data indicates the electropositive Ir NCs, owing to the electron transfer from Ir to MIL-101(Fe), can interact with oxygen lone pairs, and Fourier transform infrared spectrum shows the Lewis acid sites in MIL-101(Fe) can strongly interact with C O bond, which contributes to a high selectivity for COL. This work suggests the considerable potential of synergetic effect between hollow MOFs and metal nanoclusters for selective hydrogenation reactions.

The development of a high-performance sensing material for the detection of ammonia gas is of significant importance due to its wide industrial presence and potential hazard risks. In this article, we report the synthesis of porous and hollow MoO3 (p-h-MoO3) microspheres via the oxidation of MoS2 microsphere templates, which are obtained via self-assembly of MoS2 nanosheets under hydrothermal conditions. The composition and morphology of the p-h-MoO3 microspheres are systematically characterized via microscopic and spectroscopic techniques, and our sensing tests reveals that p-h-MoO3 possesses ultrahigh responsiveness to ammonia gas, which can be further optimized via the selection of a suitable oxidation temperature and time. Additionally, the p-h-MoO3 shows minimal responses to other gaseous molecules, thereby demonstrating significant selectivity toward ammonia. The sensing mechanism of p-h-MoO3 toward ammonia is further investigated to identify the origin of its ultrahigh sensitivity and selectivity via X-ray photoelectron spectroscopy and diffuse reflectance Fourier transform infrared spectroscopy.

Cyclohexanone is widely used in coatings, pesticides, dyes, lubricants, and other industries due to its high solubility and low volatility, but designing highly active and stable heterogeneous cata...

Bioethanol is a green alternative to supply the demand for light olefins (ethylene and propylene) and aromatics (benzene, toluene, and xylenes) that can have a green label. ZSM-5 zeolite is largely used to produce light olefins and aromatics from ethanol or ethylene. The addition of metal species to ZSM-5 can tune the activity and selectivity of the zeolite to specific compounds. The influence of the incorporation of tungsten, iron, and lanthanum species on ZSM-5 was studied. The presence of tungsten species favored the formation of aromatics, while lanthanum promoted the production of light olefins. The density of acid sites and the presence of sites with intermediate strength influenced the ethylene conversion and the product distribution of the metal impregnated zeolites. Moreover, the presence of Lewis acid sites promoted the production of aromatics. However, the role played by the acid properties is dependent on the experimental conditions employed. The reaction routes were elucidated, that is, the aromatics are mainly formed through dehydrocyclization on WHZSM-5, while the olefins are produced from the reaction of ethylene and carbene species (propylene) and the dimerization of ethylene (butenes) on LaHZSM-5.

The selective elimination of radioactive cesium from complicated wastewater is imperative in view of environment and human health. Montmorillonite has been accepted as one of the most promising adsorbents for cesium purification. However, its poor selectivity still remains a major challenge. Herein, a novel montmorillonite-sulfur composite was developed via a facile one-step solvent-free method and used for Cs+ removal. Owing to the fact that soft Lewis base S2− ligand interacted more strongly with softer Lewis acid Cs+ than other cations, the capacity and selectivity towards Cs+ was significantly enhanced. In this case, a large capacity of 160.9 mg/g was achieved. The distribution coefficient value (∼4000 mL/g) was 3-times larger than that of pristine montmorillonite (∼1500 mL/g). Moreover, this composite could be easily recycled and reused within five-times recycling experiments. Therefore, this low-cost and facilely prepared composite are expected to be used for the selective removal of Cs+ from complicated wastewater containing various competing ions.