Meerwein Ponndorf Verley Reduction Research Articles

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction.

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

Post-synthesis metal (Sn, Zr, Hf) modification of BEA zeolite: Combined Lewis and Br⊘nsted acidity for cascade catalysis

Zeolites modified by Lewis acidic metal centers such as Sn, Zr, and Hf are promising catalysts for numerous reactions relevant to biorefining, such as isomerization of carbohydrates and Meerwein-Ponndorf-Verley (MPV) reduction of furans. Preferred catalysts contain these metal ions in the framework of large-pore BEA zeolite, requiring often complex multistep preparation procedures based on expensive organometallic precursors. Herein, we developed a facile approach for obtaining highly dispersed isolated Sn, Zr, and Hf incorporated in dealuminated BEA zeolite with high metal content (Si/M ratio of 50–75) via a solid-state grinding approach using simple inorganic metal precursors. The efficient incorporation of isolated metal sites in the BEA framework with high content was achieved by methanol treatment before calcination, which removes excess metal. The Lewis acid sites derive from isolated metal ions in open sites for Sn, Zr, and Hf, while Sn-modified BEA also contains closed Sn sites. The open Sn sites display the highest Lewis acidity. The Br⊘nsted acidity stems from silanols perturbed by Lewis acidic metal ions of open metal sites and the OH group connected to the open metal sites. The metal-modified zeolites are active in the cascade reductive etherification of cinnamaldehyde, involving the MPV reduction to cinnamyl alcohol and the subsequent etherification to cinnamyl propyl ether with the isopropanol solvent over Lewis and Br⊘nsted acid sites, respectively. Sn-modified BEA was the most active sample, which stems from its strongest Lewis acidity, which is crucial for the first MPV step. Sn modification of the optimized solid-state ion-exchange method was applied to various BEA zeolites with different morphologies (nanocrystalline, hierarchical, and conventional BEA), showing that pore hierarchization can further benefit cascade reductive etherification reaction.

Increase of Zr-β zeolites Lewis acidity and insights into the reactivity enhancement

Zr-β zeolites were modified with second metals to catalyze the conversion of ethanol/acetaldehyde to 1,3-butadiene. The incorporation of Ta increases the Lewis acidity of Zr-β zeolite, resulting in higher catalytic activity than that of In, Y and Ce. Furthermore, the Zr-β zeolite that was first incorporated with Zr and then Ta with a Ta/Zr molar ratio of 1.5 exhibited greater catalytic activity of 57% conversion and 75% selectivity. Activity descriptors were proposed to calculate the reactivity of key reaction steps, which served as evidence that Ta incorporation enhances the aldol condensation and MPV reduction reaction activity, thus improving catalytic performance.

Preparation of ZrO2/Na-β and ZrO2/H-β catalysts and their catalytic performance for the Meerwein–Ponndorf–Verley reaction of cyclohexanone and isopropanol

ZrO2/Na-β and ZrO2/H-β catalysts are prepared by the reflux impregnation method and are applied to the Meerwein–Ponndorf–Verley reduction of cyclohexanone and isopropanol. The catalysts are characterized by X-ray diffraction, scanning electron microscopy-energy dispersive spectrum, temperature-programmed desorption of ammonia, N2 isothermal adsorption and desorption, and inductively coupled plasma mass spectrometry. The products are identified by gas chromatography‒mass spectrometry and analyzed by gas chromatography. The experimental results showed that ZrO2/H-β exhibits higher catalytic activity for the above Meerwein–Ponndorf–Verley reduction because ZrO2/H-β has both Zr4+ and Al3+ ion acid centers, which provide the moderately strong acid needed for the reaction. Under optimized conditions, ZrO2/H-β(6) is used as the catalyst, and the conversion rate of cyclohexanone was 92.0% as determined by the area-normalized calculation based on cyclohexanone. The catalyst can be regenerated by programmed heating calcination. The conversion rate of cyclohexanone decreased to 79.4% after five recycling cycles, and its service life needs further study to be improved.

Acid Treatment for Regulating Hf Sites of the Hierarchical Hf-B-BEA Zeolite, Thereby Boosting Its MPV Reaction Performance

Catalyst engineering plays a key role in bridging gaps between the structure of the Lewis acid center and its corresponding catalytic performance. In this regard, work that has been done in tuning active sites of Hf-containing zeolites, which hold promising catalytic activity for a variety of hydrogen-shift reactions, is far from complete. Herein, a Hf-B-BEA catalyst was rapidly prepared (within hours) by a hydrothermal semi-reconstruction strategy, involving partial framework etching of parent B-BEA and Hf grafting during the reassembling process. Then, an acid treatment was performed for expelling the boron atoms from the framework; more importantly, Hf migration into the silanol nests was triggered. The acid treatment worked powerfully as the driving force for transforming the semi-framework Hf into well-defined tetrahedrally coordinated framework Hf, thus endowing Lewis acidity of the obtained Hf-BEA. Consequently, this operation greatly boosted the Meerwein–Ponndorf–Verley reduction performance of Hf-BEA, which was almost inactive over the pristine Hf-B-BEA. The rational regulation of Hf sites provides new concepts in designing Hf-containing zeolites and understanding the structural–activity relationship.

Organodiphosphonate Zr‐MOF: A highly efficient catalyst for Meerwein–Ponndorf–Verley reduction of furfural

AbstractTetraethyl p‐xylenediphosphate is used as the organic ligand to prepare the organodiphosphonate Zr‐based metal organic frameworks (ZrP‐MOF). The physicochemical characterizations of ZrP‐MOF under different hydrothermal and calcination conditions were performed by various analytical techniques. ZrP‐MOF was then employed as a catalyst for the catalytic transfer hydrogenation of furfural with alcohol as the hydrogen donor, and the preparation parameters and catalytic properties of ZrP‐MOF were investigated. Compared with fresh ZrP‐MOF, the furfural conversion of ZrP‐MOF calcined at 825 K increased from 43.5% to 95.1%. Calcination can significantly increase the Lewis/Brønsted acid ratio and enlarge the pore structure of ZrP‐MOF, which promote the furfural catalytic transfer hydrogenation reaction over Zr‐O based on the Meerwein–Ponndorf–Verley reduction.

Glucose-derived zirconium-containing mesoporous composite for efficient catalytic transfer hydrogenation of furfural to furfuryl alcohol

Meerwein-Ponndorf-Verley (MPV) reaction has been widely acknowledged to be a mild catalytic transfer hydrogenation method for selective reduction of biomass-derived furfural to furfuryl alcohol. Herein zirconium-containing mesoporous composite catalyst was developed through the combination of sol-gel process and soft templating method, in which naturally abundant glucose and F127 triblock copolymer were used as the ligand and pore-forming agent, respectively. The hydroxyl groups in glucose molecules were demonstrated to be coordinated with zirconium ion during hydrolysis-condensation of zirconium precursor, leading to the even dispersion of zirconia nanoparticles in the composite catalyst. The composite catalyst was proven to be highly efficient for catalyzing MPV reduction of furfural with the maximum furfuryl alcohol yield of 93.4% at 180 °C within 180 min in 2-propanol, which served as both solvent and reductant. The composite also showed a good reusability. After five consecutive reaction cycles, furfuryl alcohol yield was slightly reduced from 93.4% to 77.7%, but it could be recovered to 92.8% after the reused composite was regenerated with dilute alkali solution. Batch experiments and systematic characterizations demonstrated that the excellent catalytic performance of composite catalyst was determined by multiple factors mainly including the stronger Lewis acidity, a considerable amount of basic site and the rich mesoporous structure. This study provides a facile strategy to prepare multifunctional composite catalysts using naturally abundant carbohydrates as the feedstocks for lignocellulosic biorefinery.

A functionalized Hf(iv)–organic framework introducing an efficient, recyclable, and size-selective heterogeneous catalyst for MPV reduction

A newly functionalized Hf(iv)-based UiO-66 MOF (CSMCRI-KNC′) was synthesized followed by successful characterization and employed as a solid heterogeneous catalyst on MPV reduction.

Enantioselective Meerwein–Ponndorf–Verley reduction of β,γ-unsaturated α-keto esters by asymmetric binary-acid catalysis in the green solvent iPrOH

Enantioselective Meerwein–Ponndorf–Verley reduction of β,γ-unsaturated α-keto esters in iPrOH alone was achieved by using asymmetric binary-acid catalysts.

Sc(OTf)3: An efficient homogeneous catalyst for microwave-assisted transfer hydrogenation of ethyl levulinate to γ-valerolactone under mild conditions

γ-Valerolactone (GVL) is considered as a versatile platform chemical obtained from biomass refinery. In this study, eco-friendly group III metal (Sc, Y, La) triflates were examined as homogeneous catalysts for microwave-assisted transfer hydrogenation of ethyl levulinate (EL) to GVL under mild conditions. Experimental results revealed that the selectivity of GVL has a positive relationship with the Lewis acidity of metal ion, which is related to effective charge density of the metal center (3.23, 2.81, 2.60 for Sc3+, Y3+, La3+, respectively). The stronger Lewis acidity of metal ion, the higher catalytic activity of MPV reduction. Among these catalysts, Sc(OTf)3 exhibited the best catalytic activity, achieving 98.4% EL conversion and 92.4% GVL yield at 140 °C in 3.0 h. Furthermore, Sc(OTf)3 showed high stability and recyclability for at least ten reaction cycles. In addition, a plausible reaction pathway and mechanism were proposed.

New reusable heterogeneous catalyst in the MPV reduction in cyclohexenones: moderate one-pot synthesis of cyclohexenols (effect of methyl substituents)

New reusable heterogeneous catalyst in the MPV reduction in cyclohexenones: moderate one-pot synthesis of cyclohexenols (effect of methyl substituents)

On the nature of post synthetic isolated zirconium site development in *BEA framework for ethanol-to-butadiene conversion : A mechanism study

Metallosilicates with isolated framework metal sites as well as Lewis acidity, e.g., Zr-β zeolite, is proven to be one of the most active for the conversion of ethanol to 1,3-butadiene (ETB), which is a potential process for sustainable butadiene production. However the development process of isolated Zr sites in *BEA framework and their structure–activity relationship in ETB process are still under debate. In this work, three post-synthetic procedures, Liquid Phase Incorporation (LPI), Solid State Ion Exchange (SSIE), and Direct Loading were applied for isolated framework Zr sites development, and the procedure as well as catalytic performance and mechanism were systematically investigated. The isolated framework sites could be developed by Liquid Phase Incorporation (LPI) process, where calcination was the key step for Zr-O-Si bond formation, thus representing Zr incorporation into *BEA framework, accompanying the absence of Zr ion exchange. Isolated Zr framework site was the active site in ETB process, for the strong Lewis acidity upon Zr incorporation. DRIFT and TPSR results revealed that the MPV reduction of crotonaldehyde on Zr site was rate-determining in ETB process.

MOF-808 as a Highly Active Catalyst for the Diastereoselective Reduction of Substituted Cyclohexanones.

Zr-containing MOF-808 is an excellent heterogeneous catalyst for the diastereoselective Meerwein–Ponndorf–Verley reduction of substituted cyclohexanones. The presence of substituents at the 2 or 3 position of the cyclohexanone ring strongly drives the reaction towards the formation of one of the two possible isomers. For 3-methyl cyclohexanone, the available space inside the MOF pores allows the formation of the bulkier transition state leading to the thermodynamically stable 3-cis-cyclohexanol. For 2-methyl cyclohexanone, the reaction rate is much slower and the final diastereoselectivity depends on the size of the alcohol used. Finally, reduction of 2-phenyl cyclohexanone is considerable faster over MOF-808 than for any other catalyst reported so far. The large size of the phenyl favors the selective formation (up to 94% selectivity) of the cis-alcohol, which goes through a less hindered transition state.

Strong Oxophilicity of Zr Species in Zr4+-Exchanged Montmorillonite Boosted Meerwein–Ponndorf–Verley Reduction of Renewable Carbonyl Compounds

Meerwein–Ponndorf–Verley (MPV) reduction of biomass-derived carbonyl compounds is a greatly promising route for biomass valorization. Robust, facile-prepared, and cost-effective inorganic Zr-based catalysts for this transformation remain highly desirable. Herein, Zr-containing montmorillonite (denoted as Zr-MMT) was constructed by the ion exchange of Zr4+ with the interlayer cations of montmorillonite (MMT). Very interestingly, as an inorganic catalyst, the prepared Zr-MMT showed high catalytic activity for MPV reduction of various biomass-derived carbonyl compounds. Systematic investigations revealed that the excellent performance of Zr-MMT predominantly originated from more positively charged Zr species ([Zrx(OH)y(H2O)n](4x−y)+), which could boost the activation of the carbonyl group and simultaneously promote the hydrogen transfer process assisted by suitable basic sites on MMT. Notably, the preparation of Zr-MMT avoided the utilization of surfactants or expensive organic ligands, and the prepared Zr-MMT showed better or comparable catalytic performance than most reported Zr-containing catalysts, significantly enabling it to be more practical.

Enhanced sorption of carbonyl groups by zirconium hydroxide modified with polydopamine for highly selective production of alcohols via MPV reduction under mild conditions

Enhanced sorption of catalysts to enrich and activate carbonyl substrates for highly selective production of the corresponding alcohols is an important means to boost the reaction rate. Based on the properties of dopamine polymerization under alkaline conditions, three mixtures of Zr and polydopamine with different structures were in situ synthesized by adjusting the feeding order of the raw materials. The three catalysts exhibited differences in physical adsorption capacity by N2 isothermal adsorption experiments, and the introduction of polydopamine strengthened the chemisorption of furfural by zirconium hydroxide as proved by ATR-IR. Zr-PDAE showed excellent MPV reduction ability for a variety of biomass-derived aldehydes and ketones, in which 93.9 % furfural conversion and 98.2 % furfural selectivity were achieved at 120 °C for 1 h. The modification of the selective adsorption of carbonyl substrate capacity is beneficial for the value-added conversion of biomass resources.

Highly Efficient Transfer Hydrogenation of Biomass-Derived Furfural to Furfuryl Alcohol over Mesoporous Zr-Containing Hybrids with 5-Sulfosalicylic Acid as a Ligand.

The catalytic transfer hydrogenation of biomass-derived furfural to furfuryl alcohol under mild conditions is an attractive topic in biorefinery. Herein, mesoporous Zr-containing hybrids (Zr-hybrids) with a high surface area (281.9–291.3 m2/g) and large pore volume (0.49–0.74 cm3/g) were prepared using the biomass-derived 5-sulfosalicylic acid as a ligand, and they were proven to be highly efficient for the Meerwein–Ponndorf–Verley reduction of furfural to furfuryl alcohol at 110 °C, with the highest furfuryl alcohol yield reaching up to 97.8%. Characterizations demonstrated that sulfonic and carboxyl groups in 5-sulfosalicylic acid molecules were coordinated with zirconium ions, making zirconium ions fully dispersed, thus leading to the formation of very fine zirconia particles with the diameter of <2 nm in mesoporous Zr-hybrids. The interaction between the 5-sulfosalicylic acid ligands and zirconium ions endowed mesoporous Zr-hybrids with relatively higher acid strength but lower base strength, which was beneficial for the selective reduction of furfural to furfuryl alcohol. A recycling study was performed over a certain mesoporous Zr-hybrid, namely meso-Zr-SA15, demonstrating that the yield and selectivity of furfuryl alcohol remained almost unchanged during the five consecutive reaction cycles. This study provides an optional method to prepare hybrid catalysts for biomass refining by using biomass-derived feedstock.

Meerwein–Ponndorf–Verley Reduction on Zirconium(IV) Coordinated to Amberlyst-15

Meerwein–Ponndorf–Verley Reduction on Zirconium(IV) Coordinated to Amberlyst-15

Quercetin-Zirconium: A Green and Highly Efficient Catalyst for the Meerwein–Ponndorf–Verley Reduction of Furfural

Quercetin-Zirconium: A Green and Highly Efficient Catalyst for the Meerwein–Ponndorf–Verley Reduction of Furfural

A rapid synthesis of Hf-Beta zeolite as highly active catalyst for Meerwein-Ponndorf-Verley reduction by controlling water content of precursor gel

Hf-Beta is a promisingly active Lewis acid catalyst for Meerwein-Ponndorf-Verley (MPV) reduction and other important organic reactions. However, the conventional hydrothermal synthesis of Hf-Beta inevitably requires the troublesome procedure for hydrolysis of tetraethoxysilane and the long period to complete crystallization. In the present study, we applied a synthetic approach of reducing water content of precursor gel and succeeded in considerably shortening the period for crystallization of Hf-Beta using fumed silica as silicon source. By using precursor gel with H 2 O/SiO 2 = 1.4–7.6, effect of water content of precursor gel on the crystallization of Hf-Beta, the incorporation of Hf into the zeolite framework, and the catalytic performance were thoroughly investigated. Low water content was favorable for accelerating the crystallization, but unfavorable for the incorporation of Hf into the zeolite framework, resulting in poor catalytic activity. With the assistance of seed crystal, Hf-Beta with a relatively large amount of framework Hf was obtained from the precursor gel with H 2 O/SiO 2 = 6.4 in 24 h. Hf-Beta synthesized in this way showed higher catalytic activity for MPV reduction than Hf-Beta as well as Zr-, and Sn-Beta synthesized by the conventional hydrothermal method. • A new method was developed for rapid synthesis of Hf-Beta. • Highly active Hf-Beta was obtained by controlling water content in precursor gel. • An appropriate water content was necessary to suppress precipitation of Hf species. • Synthesis period was further shortened to 24 h with seed crystal. • Hf-Beta with the high Hf content showed high activity for MPV reduction.

Correlating Lewis acid activity to extra-framework aluminum species in zeolite Y introduced by Ion-exchange

Lewis acidity was introduced into zeolite Y (Si/Al = 30) by a facile ion-exchange of aluminum cations followed by calcination. X-ray diffraction and nitrogen physisorption suggest that the zeolitic framework is retained after these treatments. With an increase in the total extra-framework aluminum in the modified zeolites, there was a pronounced increase in the number of Lewis acid sites, as illustrated by FTIR spectroscopy of adsorbed pyridine and carbon monoxide, whereas no significant change in the number of Brønsted acid sites was observed. Likewise, the catalytic activity, i.e. the conversion and rate of reaction for the MPV reduction of 4-tert butyl cyclohexanone using isopropanol over zeolite catalysts, improved considerably after ion-exchange. A quantitative agreement was observed between the concentration of these introduced extra-framework aluminum species with the total Lewis acid content from pyridine-FTIR and with the initial catalytic rates. This illustrates that the newly introduced aluminum Lewis acidic species adopt an octahedral coordination under the conditions of NMR measurement and are responsible for enhanced Lewis acid catalytic activity of the aluminum exchanged zeolites. The preservation of Brønsted acid sites further endorses the charge neutrality of these extra-framework aluminum complexes.