Significant attention is paid to methyl methacrylate (MMA) synthesis via direct aldol reaction on supported Cs-based catalysts; however, the structure of active sites is still unclear. Herein, the structural sensitivity of Zr sites toward MMA production through aldol condensation of methyl propionate with formaldehyde on Cs/Zr/SiO2 was identified, which was affected by surface hydroxyl groups on SiO2. Isolated hydroxyl groups were discovered to induce the formation of well-defined Zr sites, which facilitated MMA formation, while the dimeric Zr species led to the generation of undesired methylacrolein (MAL) byproduct. It was demonstrated that a higher proportion of medium and strong Lewis acid sites could suppress MAL production through sequential H-transfer hydrogenolysis and condensation reaction. As a result, the selectivity and formation rate of MMA could be promoted by similar to 30% and similar to 2.5 folds after Zr site modification. Therefore, the local structure of active components is critical to the regulation of catalytic performance in MMA production.

Methyl methacrylate (MMA) synthesis via aldol condensation of methyl propionate with formaldehyde over Cs-based supported catalysts is intensively investigated, while the effect of their pore structures on catalytic performance still lacks in-depth understanding. Herein, series of Cs-Zr/SiO2 catalysts with different pore structures were prepared for this aldol condensation. The physicochemical characteristics of as-prepared Cs-Zr/SiO2 catalysts were characterized using physical N-2 adsorption-desorption isotherms and CO2-/NH3-TPD. In addition, the impact of pore structure on mass transfer, adsorption, and desorption of reactants and products was studied through in situ DRIFTS. The results show that the acid and base site densities elevated with the increasing pore volume. The mass transfer of reactants and products could be promoted with increasing pore size, while their adsorption energies exhibited a volcanic trend. As a result, the Cs-Zr/SiO2 catalysts having average pore diameter of 12-18 nm and acid-base balance was considered as the optimal candidate for MMA production.

Acid-base bifunctional Cs-Zr supported SiO2 exhibit high catalytic performance on aldol condensation of methyl propionate (MP) and formaldehyde (FA) toward methyl acrylate (MMA). However, the effect of structural configuration of surface active sites on the formation rate and selectivity of MMA remains unclear. In this study, a surface engineering strategy was proposed to directionally induce the formation of catalytically active centers. Comprehensive characterizations were performed to identify the structural configuration of surface active Cs and Zr sites and their influence on MMA production in combination with catalytic evaluation. It was discovered that the increased density of isolated hydroxyl groups (equivalent to Si-OH) on SiO2 support after calcination treatment promoted the formation of well-defined Si-O-Zr and Si-O-Cs structures, corresponding to the medium strong acid and weak base sites. The acid-base properties and their balance of as-prepared Cs/Zr/SiO2 catalyst could be controllably modulated by the surface hydroxyl density and Cs (Zr) loading. These highly dispersed Cs and Zr species generated through the strong interaction with hydroxyl groups facilitated the production of MMA while suppressed the undesired Methylacrolein (MAL). Consequentially, the formation rate and selectivity of MMA could reach up to 0.91 mmol/h/gCat. and 94.3 % on the optimal 1.5Cs/0.25Zr/SiO2 catalyst. Further mechanistic studies using In-situ DRIFT revealed the catalytic pathway toward MMA and MAL, confirming the activation of MP was the kinetic-relevant step.

The dispersion of active sites plays an imperative role in the promotion of catalytic performance on methyl acrylate synthesis via direct vaporous aldol condensation. Herein, a novel PEG-assisted impregnation method was proposed to synthesize Cs/Zr-SiO2 catalyst with high dispersion of acid and base sites. A series of characterization techniques including NMR, TEM, physical N-2 adsorption isotherms, XRD, XPS, NH3-/CO2-TPD, and Py-IR were used to investigate the physico-chemical properties of these prepared catalyst series. The introduction of PEG improved the specific surface area, dispersion of active sites, and density of acid and base sites, resulting in superior catalytic performance of Cs/PEG@Zr-SiO2 by comparison with that of Cs/SiO2 and Cs/Zr-SiO2. The kinetic experiments revealed that the activation energy of aldol condensation was 80.8 kJ/mol over the Cs/PEG@Zr-SiO2 catalyst. The deactivation behavior derived from carbon deposition was discovered, and the spent catalyst could be regenerated by simple thermal treatment.

The solid frustrated Lewis pairs (FLPs) catalyst is a new promising field in catalysis but replete with challenges regarding catalyst preparation and characterization. Herein, a facile acid–base reconstruction strategy is proposed for FLPs catalyst construction based on Beta zeolite. Cs + was first induced by the hydrated extra‐framework aluminum (EFAL) Lewis acid site to form unstable acid–base adducts. Then, Cs + migrates to adjacent Si‐OH and develops Si–O–Cs Lewis base species under elevated temperature while regenerating EFAL Lewis acid centers, establishing FLP structure. A spectroscopic method for competitive adsorption of acid–base molecules has been established for characterizing FLPs, and the moderate‐strong strength Lewis acid–base pairs were confirmed on 8.1Cs‐Beta‐ex by systematic characterization. This engineered FLPs catalyst demonstrates exceptional synergy in aldol condensation of methyl acetate and formaldehyde to methyl acrylate, achieving a 5.8‐fold enhancement in STY versus conventional impregnated catalysts at ca. 8 wt% Cs loading.

Production of methyl methacrylate (MMA) from hazardous acetone cyanohydrin method is gradually limited considering the environmental sustainability. Herein, we developed a kind of Al-modified Cs-Zr/SiO2 acid-base bifunctional catalyst prepared by co-impregnation method for direct vaporous aldol condensation of methyl propionate with formaldehyde toward MMA. Multiple characterizations were performed for measurement of physicochemical properties and catalytic mechanism. The strong acid sites could be effectively reduced after the introduction of Al component, suppressing the undesired methyl acrylaldehyde (MAL). The Si-O-Cs structure was identified as active base sites for methyl propionate activation, while the Si-O-Zr and Si-O-Al framework were confirmed as acid sites for formaldehyde activation. After systematic optimization, the highest MMA space-time yield of 3.10 mmol center dot h-1 center dot g-1 with 89.6 % selectivity was achieved. Kinetic studies revealed the reaction orders of 1.18 and 1.02 for MP and FA, respectively, with activation energy of 67.1 kJ/mol. The catalyst deactivation derived from carbonaceous deposition could be regenerated by thermal treatment.

Effective strategy is intensively desired to construct efficient and durable catalytic system for mild aldol condensation between aldehydes, considering the profound significance in synthesis of high-valued a, /3-unsaturated aldehydes. Although series of mild catalytic systems using secondary amine-based catalysts have been proposed, the compatibility of high catalytic selectivity and durability still troubles the researchers in this field. Here, we developed a protonated diethanolamine ionic liquid catalyzed mild aldol reaction system with reasonable regulation of ion pair strength and ionic cluster microenvironment based on the deep insights into proton shuttle effects to improve catalytic selectivity and durability for the probed methacrolein synthesis. The interplay between the cation and anion mediated proton shuttle was elucidated by detailed kinetics derived from in situ Raman spectroscopy and theoretical calculations. Further experimental and characterization facts combined with molecular dynamic simulations identify the weak interaction of cation-anion pair and metastable worm-like cluster microenvironment facilitate proton shuttle and thus improve catalytic performance and durability. Consequently, the formation rate of methacrolein was enhanced by one fold, while overall side reaction rates were reduced by 27.5% compared to the conventional sec-amine catalyst. Additionally, this strategy also exhibited significant promotion in catalytic activity, selectivity, and durability in synthesis of the other representative a, /3-unsaturated aldehydes. These findings will offer reference for the construction and modulation of ionic liquid catalyzed mild aldol reaction system utilizing proton shuttle effects.

ObjectiveM50 steel, as a prevailing material for aero-engine bearing rings, typically undergoes cold ring rolling prior to quenching and tempering to achieve ring formation. However, due to the high deformation resistance of M50 at ambient temperature, conventional cold ring rolling processes under large deformation conditions are prone to induce micro-and nano-scale damage, adversely affecting grain refinement and thereby limiting the inheritance of microstructural characteristics during subsequent quenching and tempering, resulting in constrained enhancement of mechanical properties. Thus, a method has been proposed to further enhance the grain refinement of M50 steel under identical cold ring rolling parameters through electro-pulse assistance, thereby improving the microstructural heredity effect during its quenching and tempering process.MethodsThe electric pulse-assisted cold ring rolling-quenching and tempering (EPCRR-QT) process was employed, wherein pulsed electric current was synchronously applied during cold ring rolling to further optimize the microstructure. The evolution behavior of the microstructure during quenching and tempering was systematically analyzed.ResultsThe findings indicate that compared with specimens subjected to conventional cold ring rolling followed by quenching and tempering, those processed via EPCRR-QT exhibited a 15.2% refinement in prior austenite grain size. Additionally, reductions are observed in retained austenite content, Mo2C carbide content, and the fraction of low-angle grain boundaries. Correspondingly, Vickers hardness values increase by 4.7% in the quenched state and 4.4% in the tempered state.

With the development of green chemistry, researchers are eager to develop separable and recyclable catalyst for methyl propionate production through ethylene hydroesterification. Herein, a novel zeolite-encapsulated Pd complex was developed for ethylene hydroesterification with CO and methanol to methyl propionate. The introduced Pd component is coordinated with 1, 2-bis (di-tert-butyl phosphinomethyl) benzene ligand to form Pd complex, which is encapsulated in USY zeolite. This scheme solves the challenge of coupling phosphinepalladium complexes with acid promoters as heterogeneous catalysts. It was found that the increasing density of Br & Oslash;nsted acid sites on USY zeolite favors the ethylene hydroesterification. Furthermore, the influences of catalyst preparation and reaction conditions on the catalytic performance were assessed. As a result, the ethylene conversion could reach 99 % with MP selectivity of 100 % under the optimal condition. In addition, the catalytic heterogeneity and stability of zeolite-encapsulated Pd complex were investigated.

Although the nickel-based catalyst is able to exhibit comparative catalytic activity to noble metal for methyl acrylate hydrogenation, it requires strict reaction condition, which can be improved by regulation of coordination environment. In this study, we constructed a kind of Ni single-atom coordinated with N and S (Ni-NSC) through the pyrolysis of organic Ni-based precursors at 600 degrees C. The existence and fine structure of Ni single-atom were confirmed by the spherical electron microscopic observation in combination with the X-ray absorption spectroscopy (XAS) characterization. In addition, the catalytic hydrogenation assessment suggested that the as-prepared Ni-NSC catalyst exhibited higher activity and stability than the Ni/NSC supported catalyst prepared by incipient wetness impregnation method. This remarkable catalytic activity was due to the high dispersion and density of Ni single-atom and weak adsorption energy of intermediates on these Ni sites.

Diethanolamine as a secondary amine can effectively catalyze mild synthesis of methylacrolein (MAL) from propionaldehyde and formaldehyde via the Mannich reaction. However, the undesired cyclization of the iminium intermediate inhibits MAL selectivity due to the inherently high reactivity of hydroxyl groups. In this work, thermodynamic and kinetic insights into the side cyclization occurred during the diethanolamine-catalyzed synthesis of MAL. Three types of cyclization compounds generated from diethanolamine and formaldehyde, propionaldehyde, and MAL were confirmed by FT-IR, GC-MS, ESI-MS, and NMR characterizations. Furthermore, thermodynamic analysis for these reversible cyclization reactions was performed using the enthalpy, entropy, and Gibbs free energy estimated by the group contribution method, revealing that the cyclization is exothermic and spontaneous over a broad range of reaction temperatures. With thermodynamic equilibrium constants in hand, detailed kinetic studies were carried out for the determination of reaction orders, pre-exponential factor, and activation energy. The obtained thermodynamic and kinetic information will be useful for the further optimization of the reaction process.

Development of an effective and low-loading Ni-based catalyst is of great significance for methyl acrylate (MA) hydrogenation to methyl propionate (MP), which is a crucial step in coal-based methyl methacrylate production. In this study, we prepared a series of phosphorus-modified NiMo/gamma-Al2O3 catalysts with low loadings using the incipient-wetness impregnation method for efficient hydrogenation of MA. Multiple characterization techniques, including XRD, BET, XPS, TEM, H2-TPR, and in situ DRIFT, were employed to reveal the promotional effect of the phosphorus component on the physicochemical properties of the as-prepared catalyst. It was revealed that the introduced phosphorus species facilitated the dispersion of Ni and Mo elements, the prevention of NiAl2O4 formation, and the increase in catalytic surface area and reducibility. As a result, the yield and selectivity of MP could reach nearly 100% on the catalyst composition of 3 wt % Ni, 3 wt % Mo, and 4 wt % P (3Ni-3Mo-4P/gamma-Al2O3) prepared using H3PO4 as the phosphorus source at 80 degrees C and 0.8 MPa, and the catalytic stability could be maintained for over 100 h. In addition, the loading amounts of Ni and Mo species could be reduced by 2/3 compared with our previously reported results. In situ DRIFT studies indicate that phosphorus modification enhances MA hydrogenation by aiding its strong adsorption and hydrogen activation on Ni-Mo active sites, leading to a faster surface reaction and MP formation.

Selective oxidation of methylacrolein (MAL) to methacrylic acid (MAA) is a crucial step in the production of methyl methacrylate from isobutene. Herein, a kind of NH4 +-containing Keggin-type phosphomolybdenum heteropoly acid was modified by Ce4+ as a countercation through a one-pot method for selective oxidation of MAL to MAA. Multiple characterizations including FT-IR, XRD, physical N2 adsorption and desorption, H2-TPR, NH3-TPD, O2-TPD-MS, and XPS were employed for systematical analysis of physicochemical properties. The effects of cerium content and calcination temperature on the catalytic performance of the as-prepared phosphomolybdenum heteropoly acid were demonstrated in combination with the comprehensive characterization results. It was found that the cerium was doped to replace the H+ in phosphomolybdenum heteropoly acid, leading to the modulation of acid properties (both Br & oslash;nsted and Lewis acid site densities) and redox behavior of molybdenum species. Specifically, the MAA yield and selectivity showed a linear relationship with the reduction capability of Mo6+ to Mo5+ and strong acid site density, respectively. As a result, the MAA yield could reach up to 50% with MAA selectivity of 61% on the modified catalyst, which was enhanced by 14% and 15%, respectively, compared with the pristine one.

The design of efficient Cs-based supported catalysts is significantly crucial for methyl methacrylate (MMA) synthesis via direct aldol condensation. Herein, a type of Cs/Zr-SiO2 bifunctional catalyst with atomic Cs dispersion and ZrO2 nanoparticle sites was prepared through the strong electrostatic adsorption (SEA) method. A series of characterizations, including HAADF-STEM, XRD, XPS, MAS NMR, CO2/NH3-TPD, and Py-IR, were performed to measure the physicochemical properties of the as-prepared catalyst samples. The Si-O-Cs centers, Si-O-Zr sites, and ZrO2 nanoparticles were identified as Lewis base and acid sites for the catalytic activation of methyl propionate and formaldehyde, respectively. The acid-base properties and their balance could be controllably modulated by Cs and Zr loadings to suppress undesired byproducts. Specifically, as high as 70.0% conversion of methyl propionate, with around 91.8% selectivity for MMA, could be achieved on the optimal catalyst, with Cs loading remarkably decreased by more than twofold compared with that prepared by the traditional incipient-wetness impregnation method.

It is of great significance to determine the deactivation behavior for the development of highly efficient and stable catalysts. In this work, the deactivation and regeneration experiments were investigated for NiMo/gamma-Al2O3 catalysts during the hydrogenation of methyl acrylate at 80 degrees C, 1 MPa H2, n(H2)/n(l) = 10, and WHSV = 1 h-1. Multiple characterization techniques, including XRD, UV-vis DRS, H2-TPR, XPS, TEM, and TG, were employed for the analysis of deactivated and regenerated catalysts. The fresh catalysts exhibited good catalytic hydrogenation performance with a 99.7% yield of methyl propionate and 1002 h time-on-stream stability; however, the catalytic durability after the first and second regeneration is remarkably decreased to 600 and 299 h. The detailed analysis results demonstrated that the first-stage deactivation of the catalyst was attributed to the deposition of carbonaceous compounds on catalyst surface during the hydrogenation process. While the second- and third-stage deactivation should be caused by carbonaceous accumulation, formation of NiAl2O4 through strong interaction between the Ni species and Al2O3 support, and sintering of active component particles, which may be due to the loss of molybdenum. Specifically, the catalyst deactivation derived from carbon deposition can be recovered under thermal treatment at 450 degrees C, but NiAl2O4 generation and active component aggregation are irreversible.

The one-step synthesis of methyl acrylate (MA) via the aldol condensation of methyl acetate (Ma) and formaldehyde (FA) has garnered considerable attention recently. Nevertheless, expensive Cs-based catalysts dominate this field, and challenges exist with alternative alkali metal-based catalysts. Herein, the K/Beta catalyst was tailored for the catalytic transformation of methyl acetate and formaldehyde into methyl acrylate. A series of bifunctional catalysts with varied acid-base characteristics were prepared through the introduction of the alkali metal K on the acidic Beta zeolite support. Unprecedentedly high methyl acrylate space time yield (5.95 mmol/h/gCat) has been achieved on the K-type catalyst, with a 35.6% methyl acetate conversion and 83.7% methyl acrylate selectivity. The physicochemical properties of the prepared K/Beta catalyst were fully characterized by ICP, XRF, N2 adsorption-desorption isotherm, NH3-TPD, CO2-TPD, Py-IR, XRD, and XPS. The distribution and evolution of potassium species on catalysts having different K loadings have been investigated. The correlation between the acid-base properties of K/Beta catalysts and their catalytic performance on the aldol condensation was revealed. In addition, the effects of reaction parameters and catalyst preparation conditions on the catalytic performance were systematically researched, and the corresponding optimal conditions for K/Beta catalyst have been proposed. The kinetics of aldol condensation reactions of methyl acetate and formaldehyde on different catalysts were studied.

Electronic properties of active sites profoundly influence catalytic production of value-added chemicals; however, rational description and modulation is still a significant challenge. Herein, we propose an effective metal-ion-chelation strategy guided by density functional theory prediction and in situ Raman observation to structurally tailor and quantitatively correlate the electronic properties of active sites in ionic liquid. Comprehensive characterizations and theoretical calculations, in combination with electronic properties-performance correlations, reveal the electronic peculiarity of nitrogen and oxygen centers can be controllably restructured for remarkable improvement of catalytic performance at near-ambient condition. The turnover frequency is increased by two folds with deactivation rate suppressed by more than one half, while the kilogram-scaled recycling pilot achieves similar performance for the probe methacrolein synthesis. This strategy further exhibits excellent applicability and tolerance in other substrates with representative functional groups. Our work expresses the significance of electronic properties and provides a valid regulation approach for ionic liquid catalysis.

The production of methyl methacrylate (MMA) via one-step gaseous aldol condensation of methyl propionate (MP) and formaldehyde (FA) has received wide attention. Herein, series of polyethylene glycol (PEG) promoted Cs-Zr/SiO2 catalysts were developed and characterized by XRD, FT-IR, HR-TEM, BET, NH3-/CO2-TPD and Py-IR etc. The dispersion of active acid and base sites and their balance in catalyst could be significantly improved with the addition of PEG, which facilitated the activation of reactants and conversion towards product MMA. Furthermore, the relationship between the acid-base properties and catalytic performance was revealed, the acid and base sites were responsible for the decomposition of trioxane, which was used as the source of FA, and transformation of MP, respectively. The in-situ DRIFTS experiments unraveled two catalytic pathways through the synergistic effects between the acid and base sites during the aldol condensation of MP with FA to MMA. Kinetic studies revealed that the activation energy of this aldol condensation on the optimal catalyst is 97.9 kJ/ mol, with the reaction order of 0.98 and 1.18 corresponding to MP and FA. Deactivation behavior studies demonstrated that the decrease of catalytic activity as a function of time-on-stream was resulting from the deposition of predominant amorphous carbon instead of the loss of active components.

Supported Cs-based catalysts are considered as potential candidates for methyl methacrylate (MMA) synthesis via one-step aldol condensation, but they suffer from low activity. In this paper, the acid-base properties of the Cs/SiO2 catalyst were modulated by loading different amounts of the Al element. The changes in structural and physicochemical properties following Al introduction were revealed by a series of characterizations. In-depth investigation of the catalytic mechanism through in situ DRIFT combined with DFT calculations unveiled the synergistic effects between the Al and Cs components on the promotion of catalytic performance. The results showed that the presence of Al species facilitated the formation of weak and medium acid and base sites, along with the dispersion of the active Cs component, leading to an improvement of MMA yield. Additionally, the kinetic studies indicated that the addition of Al efficiently reduced the activation energy in comparison to pristine Cs/SiO2.

Synthesis of methyl methacrylate (MMA) by aldol condensation of methyl propionate (MP) with formaldehyde (FA) has received researchers' attention in recent years. Herein, a kind of acid-base bi-functional Cs/Ti-SiO2 was developed for the conversion of MP and FA to MMA. A series of Cs/Ti-SiO2 samples with different acid-base properties were prepared by changing the loading amount of Cs and Ti elements and characterized using XRD, BET, FT-IR, DR UV-vis, SEM, TEM, XPS, CO2/NH3-TPD, O2-TPO, py-IR, and TGA. The introduction of Ti species could significantly regulate the acidity and affect the surface structure of catalyst, facilitating the acti-vation of reactants and aldol reaction effectively. The relationship between the acid-base properties and catalytic activity was correlated, which revealed the crucial role of weak and medium acid sites in this transformative process. The production of MMA was optimized by using response surface methodology (RSM) based on the Box-Behnken design (BBD) approach. As a result, 62.8 % yield of MMA with selectivity of 75.6 % could be achieved at optimal reaction conditions. The catalyst would suffer deactivation from carbon deposition, which could be easily regenerated by simple thermal treatment without any decrease in initial activity during 600 h time-on -stream. Kinetic studies unraveled the activation energy of aldol condensation was 112.2 kJ/mol.