Dehydration Activity Research Articles

An Effective Synthesis of Phosphated Silica (PO<sub>4</sub>/SiO<sub>2</sub>) Catalyst and its Performance for Converting Ethanol into Diethyl Ether (DEE)

Research on phosphated silica (PO4/SiO2) as a heterogeneous acid catalyst in the dehydration reaction of ethanol into diethyl ether has been carried out. The PO4/SiO2 was prepared from TEOS by a wet impregnation method with various concentrations of H3PO4 (1, 2, 3, 4 M) and calcination temperatures (400, 500, and 600 °C) to obtain it with an optimum acidity. Afterward, the catalysts were characterized by FTIR, XRD, SEM-EDX, SAA, and TG-DTA. Ethanol dehydration was run using a fixed-batch reactor with a flow of N2 gas, and GC determined the selectivity of diethyl ether. The PS-4-400 catalyst had the highest activity and selectivity in the ethanol dehydration to diethyl ether at a temperature of 225 °C, with a conversion of 58.00% and a DEE selectivity of 3.71%.

Efficient Dehydration of 1-Phenylethanol to Styrene by Copper(II) and Zinc(II) Fused-Bisoxazolidine Catalysts.

The air-stable copper(II) catalyst [Cu(mesoFOX-L1)(MeCN)][OTf]2 (2a) is prepared from a fused meso-dipyridylbisoxazolidine (mesoFOX-L1) and CuBr2, followed by treatment with AgOTf. The compound is a catalyst for the dehydration of 1-phenylethanol to styrene (+H2O) in over 95% yield at 1 mol % catalyst loading. Other alcohols (benzylic, tertiary, or allylic) are also efficiently dehydrated by this catalyst. Water separation in toluene solvent is found to play an important role in the reaction. Related compounds with Zn(II) have been prepared and display reduced dehydration activity.

Conversion of Isopropanol to Diisopropyl Ether over Cobalt Phosphate Modified Natural Zeolite Catalyst

This study aims to produce diisopropyl ether (DIPE) via isopropanol dehydration using cobalt-phosphate-supported natural zeolite catalysts. The catalytic activities of the zeolite/CoO and zeolite/Co(H2PO4)2 were compared. The as-prepared catalysts were assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, and N2 adsorption-desorption. Surface acidity was determined using the gravimetric method with pyridine as the probe. The results of this study showed that natural zeolite was favorably impregnated by CoO and Co(H2PO4)2 species. The impregnation process affected the textural and acidic features of the catalysts. The zeolite/Co(H2PO4)2 catalyst with a loading of 8 mEq.g-1 exhibited the highest surface acidity of 1.827 mmol.g-1. This catalyst also promoted the highest catalytic activity towards isopropanol dehydration, with an isopropanol conversion of 66.19%, DIPE selectivity, and yield of 46.72% and 34.99%, respectively. The cobalt phosphate species promoted higher catalytic activity for isopropanol dehydration than the CoO species. This study demonstrated the potential of cobalt phosphate-supported natural zeolite catalysts for DIPE production with adequate performance. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Strong absorption of silica over full solar spectrum boosted by interfacial junctions and light–heat–storage of Mg(OH)2–(CrOx–SiO2)

Strong absorption of near-infrared (NIR) light is essential for efficient solar energy applications. NIR absorption primarily depends on the surface plasmon resonance of incident light with free charge carriers (FCCs). We demonstrated that S-scheme interfacial junctions (IJs) can substantially enhance FCC density, light-harvesting, photocurrent intensity, long lifetime of the charge carriers and photothermal effects, paving a way for novel light-material design. Abundant S–scheme IJs are constructed in CrOx–SiO2 nanoparticles, which increase the FCCs outstandingly and enhance light absorption exceptionally over the entire solar spectrum. IJs’ construction enables silica to harvest solar energy strongly. Doped with multifunctional CrOx–SiO2 nanoparticles, the photothermal-dehydration conversion and the stored heat of Mg(OH)2 can be improved by 7.0- and 5.1-times upon 30-min irradiation, respectively. The reversibility of the photothermal charge–discharge cycles of Mg(OH)2 improves 19.3 times. The thermal-storage kinetics is substantially improved owing to the reduction of the dehydration activation energy (−15.2 %). Mg(OH)2–CrOx–SiO2 composite is an excellent one-step system of light–heat–storage.

Fe/LiNO3/TiN co–modified MgO for enhanced thermochemical energy storage performance in MgO/Mg(OH)2 cycles

MgO/Mg(OH)2 thermochemical energy storage can convert solar energy and industrial waste heat into forms that are easier to store and transport by cyclic hydration/dehydration reactions. To achieve excellent energy storage performance, cyclic stability and optical absorption capability of MgO/Mg(OH)2, Fe/LiNO3/TiN co–modified MgO were synthesized for energy storage cycles by wet-mixing method. The energy storage performance, cyclic stability and dehydration kinetics of Fe/LiNO3/TiN co–modified MgO were studied in dual fixed–bed system and simultaneous thermal analyzer. The experimental results show that the Fe and LiNO3 in the composite not only increase the hydration conversion of MgO by 6.3 times at 30 min, but also reduce the dehydration temperature and dehydration activation energy of Mg(OH)2 by 99.4 °C and 64 %, respectively. TiN overcomes aggregation of MgO and sustains the excellent porous structure, which results in only a 9 % decrease in energy storage performance of Fe/LiNO3/TiN co–modified MgO after 15 energy storage cycles. Subsequently, TiN significantly strengthens the optical absorption performance of Mg(OH)2 and photothermal temperature under xenon-lamp simulated sunlight radiation. Furthermore, density functional theory calculation reveals that Fe and Li enhance the adsorption of H2O on MgO model and reduce energy barrier for hydration reactions by 62.76 %, while TiN effectively inhibits MgO clusters migration within the material and enhances the optical absorption coefficient. Hence, Fe/LiNO3/TiN co–modified MgO shows significant research value in MgO/Mg(OH)2 energy storage process.

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.

Influence of Acid‐Base Characteristics of Different Structural‐Type Zeolites (FER, MFI, FAU, BEA) on Their Activity and Selectivity in Isobutanol Dehydration

AbstractThe different structural‐type zeolites (FER, MFI, FAU, BEA) are investigated as catalysts in (bio)isobutanol conversion into linear butenes. The zeolites’ structure and morphology are confirmed by XRD, N2 (77 K) ad(de)sorption, SEM, EDX, XPS, and 27Al, 29Si, 1H MAS NMR, 1H‐29Si CP MAS NMR. The nature and strength of acid‐base sites are determined by FTIR spectroscopy of adsorbed pyridine, potentiometric titration, and TPD of NH3/CO2/H2O with MS control. The acid‐base properties of the zeolites′ surfaces influence their catalytic properties in the target process. The higher selectivity towards linear butene isomers achieved over FER and MFI can be explained by the high strength and density of Brønsted acid sites (over 90 % of the total surface acidity). MFI might be regarded as a potential material for the creation of novel catalysts for isobutanol conversion into linear butenes at moderate temperatures (448–473 K) since it offers greater operating stability throughout the process.

CAH3 from Chlamydomonas reinhardtii: Unique Carbonic Anhydrase of the Thylakoid Lumen.

CAH3 is the only carbonic anhydrase (CA) present in the thylakoid lumen of the green algae Chlamydomonas reinhardtii. The monomer of the enzyme has a molecular weight of ~29.5 kDa with high CA activity. Through its dehydration activity, CAH3 can be involved either in the carbon-concentrating mechanism supplying CO2 for RuBisCO in the pyrenoid or in supporting the maximal photosynthetic activity of photosystem II (PSII) by accelerating the removal of protons from the active center of the water-oxidizing complex. Both proposed roles are considered in this review, together with a description of the enzymatic parameters of native and recombinant CAH3, the crystal structure of the protein, and the possible use of lumenal CA as a tool for increasing biomass production in higher plants. The identified involvement of lumenal CAH3 in the function of PSII is still unique among green algae and higher plants and can be used to understand the mechanism(s) of the functional interconnection between PSII and the proposed CA(s) of the thylakoid lumen in other organisms.

High-yield synthesis of 2,5-Furandicarboxylic acid from fructose via a two-step strategy without 5-Hydroxymethylfurfural isolation using dioxane as a bridging solvent

2,5-Furandicarboxylic acid (FDCA) is a crucial bio-platform molecule for renewable polymers and fine chemicals. Here, a two-step method including fructose dehydration and 5-hydroxymethylfurfural (HMF) oxidation has been reported as an effective strategy to produce FDCA with high yield from fructose directly. In this method, for fructose dehydration over CH3SO3H, tetramethylammonium chloride (TmaCl) was first used as phase modifier and co-solvent in a H2O-dioxane biphasic-solvent system, affording HMF yield up to 90.6 % under mild condition (383 K) with relatively high fructose concentration (e.g. 5–10 wt %). Detailed 13C NMR studies verified the interaction between TmaCl and fructose, which significantly promoted the proportion of fructofuranoses and helped to improve the fructose dehydration activity and HMF yield. After dehydration step, more than 97.8 % of CH3SO3H were recovered in reaction phase for catalyst reuse, while the dioxane solution of extracted HMF was separated via simple phase separation. Followed by water commixing, this HMF dioxane solution (with the HMF concentration of 6.3 wt %) was directly oxidized over Ru/C (393 K, 1 MPa O2) to produce FDCA without HMF isolation and alkali addition, affording FDCA yield near 90 %. This study integrates the fructose dehydration and HMF oxidation rationally via dioxane as the bridging solvent to achieve high FDCA yield without complex HMF purification steps, and thus proposes an applicable model for high-efficient production of FDCA in practice.

Ni and Sr modified ZSM-5 catalyst with enhanced catalytic activity for selective dehydration of bio-derived ethanol to ethylene

Ni/Sr-ZSM-5 catalyst was synthesized with tuned acidity and improved hydrothermal stability desired for the dehydration of dilute ethanol. Operating conditions were established to maximize the ethylene selectivity from ethanol dehydration by controlling side reactions, using 6% aqueous ethanol as a model feedstock for fermenter broth. Detailed characterization data of the catalyst reveals that Ni in the catalyst is responsible for the enhanced, near quantitative ethylene selectivity at optimum reaction conditions (temperature of 250 °C, 9 h−1 WHSV), the Ni/Sr-ZSM-5 catalyst exhibited >96% conversion of ethanol with 95% yield of ethylene, facilitated by discouraging undesired side reactions of ethanol. The role of Sr is observed to improve the hydrothermal stability of the catalyst, allowing it to function even in the presence of 94% water in the feed at operated reaction conditions, as evidenced by its stable operation in the studied period of 30 h without significant loss in catalytic activity. The rate of ethylene formation with Ni/Sr-ZSM-5 was 5.33×10 −3 molgcat−1s−1, which is higher than neat H-ZSM-5. This study highlights the production of ethylene from low concentration feedstock using a catalyst with enhanced catalytic activity even in the presence of water in the feedstock.

Cooperation of an external carbonic anhydrase and HCO3- transporter supports underwater photosynthesis in submerged leaves of the amphibious plant Hygrophila difformis.

HCO3- can be a major carbon resource for photosynthesis in underwater environments. Here we investigate the underlying mechanism of uptake and membrane transport of HCO3- in submerged leaves of Hygrophila difformis, a heterophyllous amphibious plant. To characterize these mechanisms, we evaluated the sensitivity of underwater photosynthesis to an external carbonic anhydrase (CA) inhibitor and an anion exchanger protein inhibitor, and we attempted to identify components of the mechanism of HCO3- utilization. We evaluated the effects of the external CA inhibitor and anion exchanger protein inhibitor on the NaHCO3 response of photosynthetic O2 evolution in submerged leaves of H. difformis. Furthermore, we performed a comparative transcriptomic analysis between terrestrial and submerged leaves. Photosynthesis in the submerged leaves was decreased by both the external CA inhibitor and anion exchanger protein inhibitor, but no additive effect was observed. Among upregulated genes in submerged leaves, two α-CAs, Hdα-CA1 and Hdα-CA2, and one β-carbonic anhydrase, Hdβ-CA1, were detected. Based on their putative amino acid sequences, the α-CAs are predicted to be localized in the apoplastic region. Recombinant Hdα-CA1 and Hdβ-CA1 showed dominant CO2 hydration activity over HCO3- dehydration activity. We propose that the use of HCO3- for photosynthesis in submerged leaves of H. difformis is driven by the cooperation between an external CA, Hdα-CA1, and an unidentified HCO3- transporter.

Acidic property and gas-phase glycerol-dehydration activity of WO3/Al2O3 catalysts

The acidic property of WO3/Al2O3 catalysts loaded with WO3 (5–37 wt%) and their activity for gas-phase glycerol dehydration were investigated. Temperature-programmed desorption of NH3 revealed the formation of weak acid sites (the enthalpy of NH3 desorption; ΔHNH3 <110 kJ mol–1) on WO3/Al2O3. Infrared spectra of adsorbed pyridine indicated that a part of Lewis acid sites of WO3/Al2O3 was converted to Brønsted acid sites by water vapor treatment. The ΔH‡–ΔS‡ relationship for glycerol dehydration over WO3/Al2O3 and H-ZSM-5 indicated a weaker interaction of WO3/Al2O3 catalyst with the reaction intermediate than that of H-ZSM-5. The coke species deposited over WO3/Al2O3 and H-ZSM-5 were confirmed to consist of C3–C4 compounds, acrolein, benzene, toluene, xylene, glycerol, indenes, naphthalenes, and anthracenes (or phenanthrenes); fewer polyaromatic compounds were formed over WO3/Al2O3. For WO3/Al2O3, the weak acid strength of the Brønsted acid sites resulted in high durability for glycerol dehydration.

Mechanistic Investigations into the Catalytic Mode of a Dehydratase Complex Involved in the Biosynthesis of Lantibiotic Cacaoidin

Comprehensive SummaryDehydration of serine/threonine residues necessitates the activity of a dehydratase enzyme (domain) during the biosynthesis of RiPP. Recently, it was reported that dehydration in the thioviridamide pathway relies on a distinct dehydratase complex that showcases the activities of a phosphotransferase TvaC for serine/threonine phosphorylation and a lyase TvaD for subsequent phosphate elimination. Herein, we report that dehydration reactions in the pathway of lantibiotic cacaoidin involves a similar dehydratase complex, CaoK/CaoY. Remarkably, this dehydratase complex exhibits flexible enzymatic activity and tolerates significant variations in its substrate peptide sequence. By binding with the leader peptide (LP) sequence of precursor peptide CaoA, the dehydration reactions proceed in a directional manner from the C‐terminus of the core peptide (CP) to the N‐terminus, and C‐terminally truncated variants of CP are acceptable. We show that fusing CaoK to CaoY in a 1 : 1 molar ratio enables the resulting enzyme CaoYK to exert enhanced dehydration activity. CaoK binds with the LP to improve its own solubility and to ensure the phosphate transfer activity, while CaoY functions in a manner independently of LP. This work advances our understanding of the dehydration process during cacaoidin formation, and provides useful enzymes and methods for the studies of the rapidly emerging RiPPs.

Direct Detection of Paired Aluminum Heteroatoms in Chabazite Zeolite Catalysts and Their Significance for Methanol Dehydration Reactivity.

The distributions of heteroatoms within zeolite frameworks have important influences on the locations of exchangeable cations, which account for the diverse adsorption and reaction properties of zeolite catalysts. In particular for aluminosilicate zeolites, paired configurations of aluminum atoms separated by one or two tetrahedrally coordinated silicon atoms are important for charge-balancing pairs of H+ cations, which are active for methanol dehydration, or divalent metal cations, such as Cu2+, which selectively catalyze the reduction of NOx, both technologically important reactions. Such paired heteroatom configurations, however, are challenging to detect and probe, due to the typically nonstoichiometric compositions and nonperiodic distributions of aluminum atoms within aluminosilicate zeolite frameworks. Nevertheless, distinct configurations of paired framework aluminum atoms are unambiguously detected and resolved in solid-state 2D 27Al-29Si and 29Si-29Si NMR spectra, which are sensitive to the local environments of covalently bonded 27Al-O-29Si and 29Si-O-29Si moieties, respectively. Specifically, two H+-chabazite zeolites with the same bulk framework aluminum contents are shown to have different types and populations of closely paired aluminum species, which correlate with higher activity for methanol dehydration. The methodologies and insights are expected to be broadly applicable to analyses of heteroatom sites, their distributions, and adsorption and reaction properties in other zeolite framework types.

Glycerol Conversion into Allyl Alcohol Using a Coke‐tolerant ZnAl2O4‐β Zeolite Catalyst: Effect of Structural, Textural, and Acidic Properties on Catalytic Stability

AbstractCatalysts with different ZnAl2O4 contents impregnated in beta zeolite were synthesized and their catalytic activity in glycerol dehydration to allyl alcohol was investigated. The materials were characterized by XRD, XRF, FTIR, DRIFTS‐ pyridine, NH3‐TPD, and N2 physisorption. In addition, the surface electrostatic potential maps were generated by a molecular mechanics approach. The XRD patterns indicated a high dispersion of the ZnAl2O4, evidenced by the absence of reflections in the diffractograms, except for the sample containing the highest spinel content. The FTIR spectra indicated the presence of zinc aluminate spinel in the zeolite matrix. The DRIFTS‐pyridine and NH3‐TPD analyses indicated that the incorporation of ZnAl2O4 modifies the acidic properties of the zeolite concerning the number, type, and distribution of acid sites. The N2 physisorption tests showed the maintenance of the micro and mesoporous properties of H‐BEA after modification, despite the reduction of the specific area and pore volume values. The samples impregnated with the ZnAl2O4 phase showed larger mesopores sizes, which may favor its catalytic performance. The catalytic tests indicated the allyl alcohol production for the impregnated materials, which the best results were obtained by the sample containing 2 % of ZnAl2O4, with 90.65 % glycerol conversion and 37 % allyl alcohol selectivity due to appropriate tuning of the acidic and textural properties, as well as the presence of basic sites evidenced by CO2‐TPD analysis and electrostatic potential maps. The presence of acid‐base sites is essential to conduct hydrogen transfer, according to the proposed mechanism, generating allyl alcohol. Finally, the results with a longer reaction period showed greater stability for the sample impregnated with low spinel content, whose coke deposition was smaller, which may be related to the larger size of secondary mesopores.

Solid acid catalysts comprising heteropoly acids supported on SiO2, TiO2 and ZrO2: A microcalorimetric investigation of catalyst acidity and new insight into the mechanism of alcohol dehydration over HPA

Keggin-type heteropoly acids (HPAs) have strong Brønsted acidity and are widely used as acid catalysts. The aim of this work is the systematic characterisation of the acid strength of HPA catalysts comprising H3PW12O40 and H4SiW12O40 supported on SiO2, TiO2 and ZrO2 with 10–100% HPA loading and testing their activity in dehydration of alcohols to gain new mechanistic insight regarding the role of bulk-type and surface-type HPA catalysis in this reaction. The HPA catalysts were prepared by impregnation from an aqueous solution and characterised using BET, XRD, TGA, DRIFTS and ICP–OES. The acid strength of HPA catalysts was determined by NH3 adsorption microcalorimetry and found to decrease in the order HPA/SiO2 > HPA/TiO2 > HPA/ZrO2. For each type of HPA catalyst, the acid strength increased with increasing HPA loading. This can be attributed to HPA-support interaction reducing the strength of HPA proton sites at low HPA loadings. The activity of HPA catalysts was tested in the gas-phase dehydration of MeOH and i-PrOH in a fixed-bed reactor. Evidence was obtained that alcohol dehydration over HPA catalysts in a steady-state flow system occurs via the surface-type rather than bulk-type catalysis as suggested hitherto. This follows from a strong correlation between the reaction rate and the number of surface proton sites in HPA catalysts.

Production of acrylic acid from Bio-Derived lactic acid over a Defect-Rich molybdenum phosphosulfide catalyst

Introducing phosphorous and sulphur with molybdenum possess molybdenum phosphosulfate (MoP|S), and the material showed significant activity and stability for the vapour phase dehydration of bio-derived lactic acid to acrylic acid. Adding excessive thiourea-raptured layer spacing creates a defect-rich catalytic structure with more edges and kinks. This disordered atomic arrangement on the basal surface enhanced the dehydration performances of MoS2 catalysts. Considering the inverse trend of acetaldehyde and AA selectivity, we can assume that the decarboxylation of LA is favoured at low temperatures, whereas dehydration is favoured at high temperatures. Rate expression governed by the power law equation was found to be the best fit during the kinetic study, and the Ea of the dehydration was 11.39 KJ/mol. A conversion of 94% with a selectivity of 91% for acrylic acid at 450 °C was achieved over the defect-rich MoS2 catalyst.

Modelling of ultrasonic assisted osmotic dehydration of cape gooseberry using adaptive neuro-fuzzy inference system (ANFIS)

In the present investigation, the cape gooseberry (Physalis peruviana L.) was preserved by the application of osmotic dehydration (sugar solution) with ultrasonication. The experiments were planned based on central composite circumscribed design with four independent variables and four dependent variables, which yielded 30 experimental runs. The four independent variables used were ultrasonication power (XP) with a range of 100–500 W, immersion time (XT) in the range of 30–55 min, solvent concentration (XC) of 45–65 % and solid to solvent ratio (XS) with range 1:6–1:14 w/w. The effect of these process parameters on the responses weight loss (YW), solid gain (YS), change in color (YC) and water activity (YA) of ultrasound assisted osmotic dehydration (UOD) cape gooseberry was studied by using response surface methodology (RSM) and adaptive neuro-fuzzy inference system (ANFIS). The second order polynomial equation successfully modeled the data with an average coefficient of determination (R2) was found to be 0.964 for RSM. While for the ANFIS modeling, Gaussian type membership function (MF) and linear type MF was used for the input and output, respectively. The ANFIS model formed after 500 epochs and trained by hybrid model was found to have average R2 value of 0.998. On comparing the R2 value the ANFIS model found to be superior over RSM in predicting the responses of the UOD cape gooseberry process. So, the ANFIS was integrated with a genetic algorithm (GA) for optimization with the aim of maximum YW and minimum YS, YC and YA. Depending on the higher fitness value of 3.4, the integrated ANFIS-GA picked the ideal combination of independent variables and was found to be XP of 282.434 W, XT of 50.280 min, XC of 55.836 % and XS of 9.250 w/w. The predicted and experimental values of response at optimum condition predicted by integrated ANN-GA were in close agreement, which was evident by the relative deviation less than 7%.

On the role of the nature and density of acid sites on mesostructured aluminosilicates dehydration catalysts for dimethyl ether production from CO2

In this work, we designed four different mesostructured acidic materials to be used as methanol dehydration catalysts for the one-pot CO2-to-DME process, in the form of physical mixtures with a Cu/ZnO/Al2O3-based commercial redox catalyst (CZA). The studied systems consist in a mesostructured γ-Al2O3 and three mesostructured aluminosilicates (namely Al-MCM-41, Al-SBA-15, and Al-SBA-16) with the same Si/Al ratio (= 15) but significantly different textural properties. The main goal of this work is to understand how the textural features can influence the acidic properties (typology, amount, strength, surface density) and, consequently, how catalytic performances can be correlated with acidic features. On this note, we found that the systems presenting both Brønsted and Lewis sites (namely the three aluminosilicates) show much better catalytic performances than γ-Al2O3, that only features Lewis sites, thus implying that Brønsted sites are more active towards methanol dehydration than Lewis sites. The three aluminosilicates, despite presenting comparable amounts of Brønsted sites, show significantly different performances in terms of selectivity to DME; particularly, Al-SBA-16, the system with the lowest surface area, proved to be the most efficient catalyst. This finding led us to infer that, besides Brønsted acidity, a high surface density of acid sites is a key factor to obtain a high dehydration activity; being methanol dehydration a bi-molecular reaction, the close proximity of two acid sites would indeed favor the kinetics of the process.

Photocatalytic Production of Syngas from Biomass.

ConspectusAs a renewable solar energy and carbon carrier, biomass exploration has received global attention. Photocatalytic valorization of biomass into fuels and chemicals is a promising and sustainable method for future chemical production. Photocatalysis has the potential to accomplish reactions under ambient conditions due to the unique reaction mechanisms involving photoinduced charge carriers and has recently been recognized as an efficient and feasible technology for biomass conversion. Biomass is widely used as sacrificial agent to scavenge holes in photocatalytic hydrogen evolution, and the carbon is eventually degraded to CO2 with a minor amount of CO. The generation of CO instead of CO2 is more economical and promising but also a challenge under photoreforming conditions.This is a new research direction, while until now there has still been the lack of a comprehensive review article to summarize and provide prospects for this topic. This Account will highlight our contributions in the research direction of the photocatalytic reforming of biomass into syngas (CO + H2). In 2020, we first reported the photocatalytic conversion of biopolyols and sugars into syngas by employing a defect-rich Cu-TiO2 nanorod photocatalyst and found that formic acid is a key intermediate to CO. Further study revealed that a facet-dependent electron-trapping state on anatase TiO2 will affect the photocatalytic dehydration activity for formic acid intermediates by regulating the electron transfer process during the reaction, and the selective generation of FA or CO from photocatalytic biomass reforming was achieved via exposing the (100) or (101) facets, respectively. Visible light-driven syngas generation was further achieved over a CdS-based photocatalyst. Sulfate modification of CdS ([SO4]/CdS) was constructed as the proton acceptor, thus efficiently facilitating the proton-coupled electron transfer process. Besides, we put forward an oxygen-controlled strategy to increase the CO generation rate without a significant decrease in CO selectivity via controlling the O2/substrate ratio. Based on this system, a Z-scheme CdS@g-C3N4 core-shell structure and CdO-CdS semicoherent interface were created to facilitate charge transfer and enhance the O2 activation, thus increasing the CO generation rate. Moreover, we also developed a photoelectrochemical approach to separately produce CO and H2 from biomass. Nitrogen doping of a hexagonal WO3 nanowire array was used to produce the photoanode. The built-in electric field generated via nitrogen doping promoted charge transfer, hence improving the efficiency of PEC reforming of biopolyols and sugars. This Account will systematically analyze the challenges in this research direction, the reaction route in the photocatalytic biomass reforming, and the factors affecting CO selectivity and give insight into the design of efficient photocatalytic systems.