Lewis Acid Strength Research Articles

Facile synthesis of bidentate boron Lewis acids by pentafluorobenzene elimination

The obtained results reveal simple synthetic approach for bidentate boron Lewis acids with the ‐OB(C6F5)2 acid group and aliphatic or aromatic linkers. Computational results showed comparable FIA for the ‐OB(C6F5)2 site in boron bidentate Lewis acids relative to initial B(C6F5)3. The relative Lewis acid strength of R[OB(C6F5)2]2 (R = C2H4, p‐C6H4, m‐C6H4) was characterized by Gutman‐Becket tests. The elimination of pentafluorobenzene by the reaction of R‐OH with B(C6F5)3 can be used for the synthesis of R‐OB(C6F5)2 derivatives and polydentate strong Lewis acids.

The role of Lewis acidity in bis(β-diketonate)zirconium(IV) complexes as catalysts for the ring-opening polymerization of δ-valerolactone

Poly(δ-valerolactone) (PVL) is a polymer that has garnered significant researcher interest due to its intriguing features and prospective uses across numerous domains, particularly in medicine. This work aimed to assess the influence of the Lewis acidity of the bis(β-diketonate)Zr catalyst complex on the ring-opening polymerization of δ-valerolactone. The ligand in the compound contains an electron-donating group, specifically the methyl group (2a). Furthermore, electron-withdrawing groups employed include phenyl (2b–2c) and trifluoromethyl groups (2d). Characterization data indicate that PVL has been successfully synthesized with a bis(β-diketonate)Zr complex catalyst. The hierarchy of Lewis acid strength for the bis(β-diketonate)Zr complex is 2c > 2b > 2d ≫ 2a. The sequence of PVL DP from highest to lowest is 2b, 2c, 2d and 2a. Nonetheless, the elevated Lewis acidity of complex 2c does not provide PVL with the greatest degree of polymerization. The steric barrier of complex 2c, which contains two phenyl groups, is larger than that in complex 2b. Consequently, the coordination process of the nucleophilic monomer with the electrophilic zirconium central atom becomes increasingly difficult.

Influence of surface properties of transition metal oxides for permanganate activation: Key role of Lewis acid sites

Permanganate (PM) activation to remove contaminants in aqueous solution has gained increasing interest, and effective approaches to enhance its oxidation ability are becoming one of the hot spots. Transition metal oxides (TMOs) stand out as the most potential catalysts, but have received little attention in this area until now. Their mechanism towards PM activation also remains controversial. In this study, a series of TMOs with diverse surface properties were synthesized, and their effectiveness was compared. It was observed that α-MnO2, NiO and Co3O4 exhibited significantly higher rates of degrading sulfadiazine, levofloxacin and phenol through PM activation than CeO2, α-Fe2O3 and CuO. A performance evolution depended on the surface Lewis acid (LA) strength was established, while a less consistent correlation was observed between the degradation rate and other surface properties. Based on electrochemical analysis and density functional theory calculations, the spontaneous adsorption of MnO4- anions on LA sites in TMOs with an increase in oxidation potential of PM was further confirmed. This research would deepen the understanding of PM activation mechanism, and offer new guidance in the design of more efficient catalysts.

Highly transparent and conductive Ga-doped InWO multi-component electrodes for Perovskite photovoltaics

Wide-bandgap Ga-doped InWO (GIWO) transparent conductive electrodes (TCE) were fabricated by co-sputtering IWO and Ga2O3, followed by rapid thermal annealing (RTA), with the effects of the Ga dopant content on the electrical, optical, structural, and morphological properties of the GIWO multi-component electrodes investigated to optimize the GIWO electrode. According to the figure of merit (FOM), the GIWO film with a Ga content of 2.1 at% exhibited a low sheet resistance of 9.9 Ohm/square and high transmittance of 91.71 % at a wavelength of 550 nm. The presence of a high Lewis acid strength (LAS) dopant of Ga (1.16) and W (3.15) led to an increase in the carrier mobility of GIWO and transmittance in the near infrared wavelength region. In addition, the strongly preferred (222) and (400) orientations of the GIWO grains increase the carrier mobility and improve the surface morphology of the GIWO electrodes. The successful operation and superior performance of the planar p-i-n structured perovskite solar cells (PSC) fabricated on GIWO electrodes indicate the feasibility of GIWO as a substitute for conventional Sn-doped In2O3 electrodes. The highest-performing PSC with GIWO electrodes exhibited reliable hysteresis with an efficiency difference of less than 1 % depending on the scan direction under standard AM1.5 G conditions.

Degradation of clofibric acid by ozonation assisted by Co-Ce-SBA-15: Role of interfacial electron migration

Restrained by the sluggish Ce redox cycle, Ce-SBA-15 exhibited the low electron transfer toward O3 activation. To this end, cobalt‑cerium co-doped SBA-15 with three-dimensional pore structure was designed using urea-assisted hydrothermal method and its activity was evaluated using Clofibric acid (CA) as target pollutant. XRD and N2 adsorption-desorption characterizations suggested that Co-Ce-SBA-15 possessed a three-dimensional pore structure with high order degree. py-FTIR, O2-TPD, H2-TPR, and in situ electrochemical characterizations indicated that compared with Ce-SBA-15 and Co-SBA-15, Co-Ce-SBA-15 had greater Lewis acid strength, electron transfer ability and oxygen reducibility. Co-Ce-SBA-15/O3 achieved the greater CA removal and mineralization rate, with 98.7 % CA removal and 58.3 % TOC removal were obtained in 90 min. Co-Ce-SBA-15/O3 process would be inhibited by the coexisting Cl−, NO3− and SO42−. Co-Ce-SBA-15 demonstrated the greater ozone utilization rate than those of monometallic SBA-15. Lewis acidic sites of Co and Ce were the main sites for activating O3. DFT results suggested that the obvious electron transfer existed among O3, Co and Ce Lewis acid sites. The conversion of Co3+/Co2+ and Ce4+/Ce3+ accelerated the interfacial electron transfer, which favored for conveying O3 into •OH. •OH was the primary reactive oxygen species involved in degrading CA. 8 kinds of intermediates were found during CA degradation and the possible degradation route was proposed. This study deepened the understanding of the cooperative effect of Co and Ce in catalytic ozonation process.

Tandem catalysis of furfural to γ-valerolactone over polyoxometalate-based metal-organic frameworks: Exploring the role of confinement in the catalytic process

Polyoxometalate-based metal-organic frameworks (POMOFs) with bifunctional Lewis-Brønsted acid were designed by confining polyoxometalates (POMs: phosphotungstic acid (PW), phosphomolybdic acid (PMo) or silicotungstic acid (SiW)) within the Zr-MOFs. The confined POMs not only have their own Brønsted acid, but can also regulate the Lewis acid strength of the POMOFs via charge regulation, ultimately allowing the POMOFs to display superior catalytic performance in the tandem catalysis of furfural (FAL) to γ-valerolactone (GVL). Among the three catalysts (POMOF-PW, POMOF-PMo and POMOF-SiW), a complete conversion of FAL was achieved, while POMOF-PW exhibited the highest GVL yield (58.1 %) at 160 °C within 23 h. The leaching experiment and structural characterization of the catalyst before and after recycling confirmed the stability of the catalyst structure. The humin originates from the polymerization of furan ring-containing compounds driven by Brønsted acid. The adsorption configuration of the substrate molecules on the catalyst offers a new explanation for the tandem reaction process, i.e. that perpendicular adsorption performs only the first step of the tandem reaction, while the coexistence of perpendicular and horizontal adsorption permits the entire reaction process. This work gives unique insights into the tandem reaction of FAL and can guide the design of efficient tandem reaction catalysts.

Insight into dehydrogenation mechanism of methanol to aromatics over GaO+/HZSM-5: Which is the active center, Lewis acid site or Brønsted−Lewis synergistic site?

The mechanisms of dehydrogenation reactions as important processes in methanol to aromatics (MTA) have been controversial. Recent work on the active center for dehydrogenation at either Lewis acid site (LAS) or Brønsted−Lewis (B−L) acid synergistic site is a matter. The dehydrogenation processes on L−acid site (GaO+) or B−L acid site (H+−GaO+) over GaO+/HZSM-5 with different Lewis acid locations for n-hexene to 1,5-hexadiene, as well as cyclohexene to benzene have been researched by applying the density functional theory (DFT) method. The results reflect that active center of dehydrogenation reactions is B−L acid synergistic site through B−L acid synergy mechanism. All elementary steps including C−H bond activation, the formation of H2, hydrogen transfer as well as the regeneration of B−acid site are easy to proceed. However, the isomerization for carbonium ions from GaO+ to skeleton oxygen of zeolites is relatively difficult. The analysis shows that isomerization is influenced by the structural and electronic properties of carbonium ions chemisorbed on zeolites. Lewis acid strength of GaO+/HZSM-5 and energy gap between HOMO and LUMO on adsorption complexes are appropriate descriptors for the C−H bond activation. The rate constants analysis indicates that increasing temperature is more favorable for C−H bond activation. Further considering that C−H bond activation occurred preferentially than isomerization, it could be a critical initial step to primarily screen catalysts.

The synthesis for adamantane derivatives of high energy density fuel catalyzed by HY zeolite based on the DFT

The adamantane derivatives are promising high-energy-density fuel due to preferable fuel properties, the activity of HY zeolite is key for synthesis adamantane derivatives on account of easy separation from liquid fuels. The effect of acid strength and type of zeolite on activity from DMTCD to 2c,2t-dimethyladamantane is investigated by the DFT method. The activity on HAlY zeolite with stronger Brønsted acid strength is superior compared to HGaY, HFeY, HInY and HBY. Thus, AlO+/HAlY zeolite is investigated obtaining that smaller gap between LUMO and HOMO leads to the better activity than HAlY. And oxoaluminum cations as Lewis acid improves Brønsted acid strength, in which the activity of AlO+/HAlY with stronger Brønsted/weaker Lewis acid strength is preferable than other HAlY with Lewis acid. Therefore, this work provides guidance for screening of HY zeolite with preferable activity of hydro-isomerization.

Cu/ZnO/Al2O3 sorbent promoted by Zr for the ultra-deep removal of thiophene in simulated coke oven gas

The ultra-deep removal of thiophene from coke oven gas (COG) is critical for the conversion of COG to methane. Currently, Cu/ZnO/Al2O3 is considered as a promising sorbent for thiophene removal; however, its desulfurization performance is currently unable to meet the requirements for industrial applications. Here, a zirconium modification strategy is proposed to overcome this problem, allowing zirconium loaded copper-based sorbents (Cu/ZnO/Al2O3/ZrO2) with significantly improved thiophene removal performance and high activity to be obtained. Characterization results showed that zirconium improved both the dispersion of copper and the concentration of Lewis acid sites on the sorbent surface. A ZrO2 concentration of 2 % resulted in stronger Cu-Zn interaction, and the dispersion of Cu on the surface of the sorbent reached its maximum value (49.20 %). Additionally, the Lewis acid strength was also maximized, which greatly improved the desulfurization activity and resulted in a breakthrough adsorption capacity of thiophene (Qb-thiophene) of 36.24 mg/g, which was about 17 % higher than that of the unmodified Cu/ZnO/Al2O3 sorbent. These results demonstrate that the sulfur capacity of the sorbent can be increased by increasing the number of acidic sites on its surface, paving the way for ultra-deep thiophene removal in industrial applications.

One pot microwave-assisted catalytic upgrading of α-angelicalactone to γ-valerolactone over scandium triflate without H2 supply

Biomass upgrading, which supplies important biomaterials, chemicals and fuels, is considered as an efficient way to realize the goal of carbon neutralization. Recently, γ-valerolactone (GVL) has gained increasing attention due to its wide applications. In this work, a novel protocol of microwave-assisted cascade catalytic upgrading of α-angelicalactone (α-AL) to GVL over metal triflate using alcohol as the hydrogen donor was proposed. The yield of GVL production from α-AL upgrading is strongly influenced by the Lewis acid strength of the metal triflate and the reduction potential of the employed alcohol. Among all tests, Sc(OTf)3 showed the best catalytic performance in isopropanol media, giving 96.4 % GVL yield and 100 % α-AL conversion at 433 K within 3.0 h. Meanwhile, kinetic study indicated transfer hydrogenation of isopropyl levulinate to isopropyl 4-hydroxyvalerate was the rate-limited step with the apparent activation energy of 94.5 kJ/mol. This Sc(OTf)3 catalyst was highly stable and could be reused for five cycles by simple vacuum distillation. In a word, this work provides an alternative for GVL production from biomass upgrading.

Functional Assessment of the Lewis Acid Strength of Structurally Complex Solid Acids

Functional Assessment of the Lewis Acid Strength of Structurally Complex Solid Acids

Attapulgite-based MCM-41 zeolite supported Ni-Nb catalysts for hydrogen production by acetic acid steam reforming

Acetic acid steam reforming (AASR) was generally considered as one of the promising technologies for hydrogen production. In this work, the L-lysine-assisted attapulgite-based MCM-41 zeolite (LAMZ) was successfully synthesized by using attapulgite-derived silicon source and the LAMZ-supported Ni-Nb (xNi-yNb/LAMZ) catalysts were prepared via conventional impregnation method. The effects of LAMZ and Nb content on regulating the microstructures and properties of Ni-based catalysts were investigated by various characterizations. Results revealed that the addition of L-lysine could contribute to forming more void structures and increasing specific surface area of LAMZ support, which was beneficial for promoting the dispersion of active sites and enhancing the metal-support interaction. Additionally, Nb optimized the reduction of Ni, increased the concentration of surface-active Ni species, improved the strength of surface Lewis acid and promoted the formation of Ni-NbOx interfaces. Amongst, 5Ni-1Nb/LAMZ exhibited the highest surface Ni0 sites and Ni-NbOx interfaces, which further induces the generation of VO generation and the flow of lattice oxygen. Therefore, the 5Ni-1Nb/LAMZ catalyst presented the highest acetic acid conversion (82.1 %) and hydrogen yield (69.9 %) at reaction conditions of reaction temperature = 750 °C, S/C = 3, WHSV = 19.96 h−1, furthermore, it almost no any inactivation during 55 h of AASR. Additionally, the characterization results of spent catalysts confirmed that 5Ni-Nb/LAMZ possess high coke resistance and anti-sinter capability.

Systematic Assessment of the Catalytic Reactivity of Frustrated Lewis Pairs in C-H Bond Activation.

Unreactive C-H bond activation is a new horizon for frustrated Lewis pair (FLP) chemistry. This study provides a systematic assessment of the catalytic reactivity of recently reported intra-molecular FLPs on the activation of typical inert C-H bonds, including 1-methylpyrrole, methane, benzyl, propylene, and benzene, in terms of density functional theory (DFT) calculations. The reactivity of FLPs is evaluated according to the calculated reaction thermodynamic and energy barriers of C-H bond activation processes in the framework of concerted C-H activation mechanisms. As for 1-methylpyrrole, 14 types of N-B-based and 15 types of P-B-based FLPs are proposed to be active. Although none of the evaluated FLPs are able to catalyze the C-H activation of methane, benzyl, or propylene, four types of N-B-based FLPs are suggested to be capable of catalyzing the activation of benzene. Moreover, the influence of the strength of Lewis acid (LA) and Lewis base (LB), and the differences between the influences of LA and LB on the catalytic reactivity of FLPs, are also discussed briefly. This systematic assessment of the catalytic activity of FLPs should provide valuable guidelines to aid the development of efficient FLP-based metal-free catalysts for C-H bond activation.

Low-field 2D NMR relaxation and DRIFTS studies of glucose isomerization in zeolite Y: New insights into adsorption effects on catalytic performance

Sn and Ga doped zeolite Y catalysts were tested for the isomerization of glucose to fructose carried out in different solvents (water, methanol and ethanol). Therein, ethanol favoured a Lewis acid site catalyzed pathway that promotes glucose isomerization to fructose, whereas methanol resulted in an equal distribution of products (mannose, fructose and alkyl fructoside). In contrast, the catalysts were totally inactive in water solvent. NMR relaxation measurements, including solvent displacement experiments, suggested that the lack of catalytic activity in water is due to the strong adsorption of this solvent within the zeolite pores blocking reactants from the Lewis acid sites active for the sugar isomerization. In comparison, ethanol adsorbs relatively more strongly than methanol, hence is retained in the pores where solvated fructose is preferentially prevented from the further reaction on Brønsted acid sites situated outside of the pore space. NMR relaxation measurements using pyridine and tetrahydrofuran (THF) and pyridine-DRIFTS measurements suggest metal doping had little effect on the overall relative acid strength of the zeolites but resulted in zeolites with increased Lewis acid strength relative to the non-doped zeolites. The results reported provide direct experimental evidence on the importance of adsorption properties of solvents within zeolites used for glucose to fructose isomerization and may serve as a starting point for a new approach towards designing and optimizing such catalytic systems.

CO2-Assisted in situ hydrogen extraction for highly selective aromatization of n-Hexane over Zn modified HZSM-5 catalyst

Controlling the evolution of H species in CO2-assisted alkane activation represents an opportunity for simultaneously upgrading light alkanes and greenhouse gas CO2. Herein, we successfully realized the highly selective aromatization of n-hexane by the assistance of CO2 over Zn modified HZSM-5 catalyst. Multi-characterizations demonstrated that the introduction of CO2 could timely remove the in situ H originated from the C-H activation of n-hexane and cyclohexane through the dynamic evolution of the pentagonal coordination Zn-OH+-(CO)-O-Zn structure. On this basis, hydrogen transfer between olefins and aromatics is effectively inhibited, and the binding between π electrons of benzene ring and hydrogen proton is weakened, accelerating the generation and desorption of BTEX. Therefore, the Zn/ZSM-5-CO2 displays a record high 49.7% BTEX yield, which is nearly 10% higher than that of the Zn/ZSM-5-N2 (40.3%). In addition, the loss of medium strength Lewis acid caused by in situ H reduction of Si(Al)-O-Zn structure is significantly reduced, ensuring its superior catalytic stability under long-term conditions. These results may provide some insights for the profitable utilization of petrochemical resources to aromatics over zeolites.

Investigation of N,N′‐Disulfopiperazinium Chlorometallates of Fe(III), Ni(II) and Co(II) as Hybrid Catalysts for the Synthesis of 1,2‐Dihydroquinazoline Derivatives

AbstractThree organic salts of N,N′‐disulfopiperazinium cation with complex metal chloride anions of Fe(III), Ni(II) and Co(II) cations were developed as Brønsted‐Lewis acidic hybrid materials in solid state. Their structural compositions were established by FT‐IR, UV‐Visible, SEM, EDX, Powder XRD and Raman techniques. Thermogravimetric analyses showed removal of physisorbed water around 100 °C for Fe(III) salt in contrast to 150–170 °C for Ni(II) & Co(II) organic salts for strongly bound water molecules in highly crystalline state. Their Brønsted acidities were determined from comparative UV‐visible spectra of 4‐nitroaniline in water in presence of the halometallates while Lewis acidity strength was observed via FT‐IR spectra of these salts in presence of pyridine as probe molecule. The catalytic activity of these acidic organic salts was investigated for three‐component synthesis of 1,2‐dihydroquinazolines as recyclable heterogeneous catalysts.

Investigation on the catalysis performance of metal-doped zeolites on ring-opening acidolysis reaction

Metal-incorporated zeolites as heterogeneous Lewis acid were applied in the ring-opening acidolysis of ethylene oxide with acrylic acid to prepare 2-hydroxyethyl acrylate (HEA). The catalysis characteristics, including Lewis acid strength and internal mass transfer resistance, were systematically investigated to facilitate the rational design of zeolite catalysts. Through modifying the Lewis acid strength of zeolites via different metals (Sn, Zr and Ti) incorporation and the internal mass transfer resistance of zeolites from the particle size, pore diameter or pore structure, it was found that the increased Lewis acidity can accelerate both the main and side reactions, resulting in the high activity but low selectivity of zeolite catalysts; the enhanced internal diffusion was the key to limiting subsequent cascade alcoholysis side reactions as well as the decline of catalytic performance. Based on these findings, Zr-containing zeolites featured with moderate Lewis acidity and uniform intracrystalline mesoporosity were designed and prepared, presenting excellent catalysis and recycling performance. These results demonstrated the great potential of the developed zeolite catalysts for the green synthesis of HEA as well as the similar ring-opening acidolysis of epoxides.

Structure-Reactivity Relationships in Borane-Based FLP-Catalyzed Hydrogenations, Dehydrogenations, and Cycloisomerizations.

ConspectusThe activation of molecular hydrogen by main-group element catalysts is an extremely important approach to metal-free hydrogenations. These so-called frustrated Lewis pairs advanced within a short period of time to become an alternative to transition metal catalysis. However, deep understanding of the structure-reactivity relationship is far less developed compared to that of transition metal complexes, although it is paramount for advancing frustrated Lewis pair chemistry.In this Account, we provide detailed insight into how Lewis acidity and Lewis basicity correlate to reactivity. The reactivity of frustrated Lewis pairs will be systematically discussed in context with selected reactions. The influence of major electronic modifications of the Lewis pairs is correlated with the ability to activate molecular hydrogen, to channel reaction kinetics and reaction pathways, or to achieve C(sp3)-H activations.First, we will describe how we entered this emerging field of research after quickly realizing that information was lacking on how the reactivity changes with modification of the frustrated Lewis pair. This led us to the development of a qualitative and quantitative structure-reactivity relationship in metal-free imine hydrogenations. The imine hydrogenation was utilized as the model reaction to experimentally determine the activation parameters of the FLP-mediated hydrogen activation for the first time. This kinetic study revealed autoinduced catalytic profiles when Lewis acids weaker than tris(pentafluorophenyl)borane were applied, opening up to study the Lewis base dependency within one system. With this knowledge of the interplay between Lewis acid strength and Lewis basicity, we developed methods for the hydrogenation of densely functionalized nitroolefins, acrylates, and malonates. Here, the reduced Lewis acidity needed to be counterbalanced by a suitable Lewis base to ensure efficient hydrogen activation. The opposite measure was necessary for the hydrogenation of unactivated olefins. For these, comparably less electron-releasing phosphanes were required to generate strong Brønsted acids by hydrogen activation. These systems displayed highly reversible hydrogen activation even at temperatures as low as -60 °C. A systematic study of these systems enabled the development of acceptorless dehydrocouplings of amines with silanes and dehydrogenations of aza-heterocycles by C(sp3)-H activations. Furthermore, the C(sp3)-H and π-activation was utilized to achieve cycloisomerizations by carbon-carbon and carbon-nitrogen bond formations. Lastly, new frustrated Lewis pair systems featuring weak Lewis bases as active components in the hydrogen activation were developed for the reductive deoxygenation of phosphane oxides and carboxylic acid amides.

Ni-Ti Intercalated and Supported Bentonite for Selective Hydrogenation of Cinnamaldehyde.

Ni-Ti intercalated bentonite catalysts (Ni-Ti-bentonite) and Ni-TiO2 supported bentonite catalysts (Ni-TiO2 /bentonite) were prepared, and the effects of Ni-Ti supported and intercalated bentonite on the selective hydrogenation of cinnamaldehyde were investigated. Ni-Ti intercalated bentonite enhanced the Brønsted acid sites strength, decreased the acid amount and Lewis's acid sites strength, which inhibited the activation of the C=O bond and contributed to selective hydrogenation of the C=C bond. When Ni-TiO2 was supported on bentonite, the acid amount and Lewis's acid strength of the catalyst increased, providing additional adsorption sites and increased the acetals byproducts. Due to the higher surface area, mesoporous volume, and suitable acidity, compared with Ni-TiO2 /bentonite in methanol solvent, 2 MPa, 120 °C for 1 h, Ni-Ti-bentonite exhibited a higher cinnamaldehyde (CAL) conversion of 98.8 %, as well as a higher hydrocinnamaldehyde (HCAL) selectivity of 95 %, and no acetals were found in the product.

Highly Selective Production of Renewable 1,3-Pentadiene from 1,4-Pentanediol over an Acid–Base (K–Ce/ZrSi) Catalyst by Adjusting the Parallel-Reaction Pathway

Selective synthesis of 1,3-pentadiene without 1,4-pentadiene formation is challenging as well as rewarding because of the widespread use of 1,3-pentadiene in adhesive, paint, and curing agent production. Herein, modified K–Ce/ZrSi catalysts with acid–base sites were synthesized for the production of 1,3-pentadiene from 1,4-pentanediol. The overall 1,3-pentadiene yield was 74.7%, while the 1,4-pentadiene yield was 1.3%. On the catalyst, two parallel routes (direct dehydration and dehydra-decyclization) for the conversion of 1,4-pentanediol to 1,3-pentadiene were disclosed. The 4-position hydroxyl group was first activated and then eliminated on the acid sites. It was considered that the acid–base sites of catalysts exhibited a synergistic effect for the selective dehydration of 1,4-pentanediol to 1,3-pentadiene, where the medium strength Lewis acid sites and weak base sites were responsible for the elimination of the hydroxyl group and the corresponding β1-H, thereby inhibiting the formation of 1,4-pentadiene. Furthermore, a plausible reaction network was proposed.