Enhancing hydrothermal stability of framework Al in ZSM-5:From the view on the transformation between P and Al species by solid-state NMR spectroscopy

HZSM-5,with good surface acidity and shape selectivity,was reported as hydrocarbon cracking catalyst for multiple decades,however the hydrothermal stability,especially dealumination of tetrahedrally coordinated framework aluminum(TFAl),has been proved extensively as one of the major challenges during reactionregeneration process.Phosphorus was proposed to stabilize TFAl and indeed it enhanced the hydrothermal stability.Unfortunately,most of the phosphorus species would remain outside of the zeolite pore,mainly as polyphosphate species,and block the micropore severely,with only a limited portion introduced into the channel being able to interact with TFAl.Enlarging the pore size by alkali treatment(desilication)is one of the most convinced methods,but the details about specific P species during alkali treatment and its transformation upon hydrothermal activation is not acquired,thus the mechanism has not been fully understood.Herein,the P-containing species and its transformation during direct P modification and acid/alkali treatment followed by Pmodification have been studied,and the mechanism on the interaction between P and Al species has been investigated,using several analytical methods,especially Solid-state nuclear magnetic resonance(SSNMR)spectroscopy.It was found that the combination of desilication and subsequent phosphorus modification can enhance the activity of the ZSM-5 for the cracking of ethylcyclohexane,due to the better hydrothermal stabilization of acid sites by the enhanced interaction between phosphorus and TFAl,resulting from the improved accessibility of TFAl because of the successful generation of mesoporosity.Whereas the acid treatment followed by phosphorus modification,with declined retention of crystallinity and P/Al ratio,monoclinic/orthorhombic transition during steam activation,and the failed generation of mesopores,would cause obvious aggregation of the phosphorus species and could not improve the hydrothermal stability of the ZSM-5 effectively,and the direct phosphatation turned out much worse.Finally,a specific index that the intensity of the signal at 39 in 27Al MAS NMR spectra before steam activation was proposed as the indicator for determining the efficiency of phosphorus modification.And the proposed mechanism on the interaction between phosphorus and TFAl during the phosphorus modification could also be applicable in other zeolites.

Environmentally-Friendly Catalytic Oxidation of Cyclohexanone with 30% H_2O_2 Solution: A Comparison Study between Hollow Titanium Silicate and Dealuminated HBEA Zeolites

Two clean liquid–phase cyclohexanone oxidation routes catalyzed by DHBEA and HTS zeolites, in the absence of organic solvents, have been developed for producing high value-added chemical intermediates. Under optimized conditions,the cyclohexanone conversion reaches up to 60%, and the selectivity of total target products(ε-caprolactone, 6-hydroxyhexanoic acid and adipic acid) is over 90% achieved by the HTS zeolite; while both cyclohexanone conversion and the 6-hydroxyhexanoic acid selectivity are over 95% obtained on the DHBEA zeolite. Both the Lewis and Br鰊sted acid sites of DHBEA zeolite can preferentially activate the carbonyl group of cyclohexanone without any impact on H_2O_2 molecules.Meanwhile, the HTS zeolite can predominantly make H_2O_2 more reactive, which agrees well with the molecular calculation results. Hence, two different Baeyer-Villiger oxidation mechanisms based on the activation of H_2O_2 and cyclohexanone are proposed. Then, 6-hydroxyhexanoic acid is formed via the ring-opening of ε-caprolactone. However, C-OH groups cannot be reactivated by DHBEA zeolite, leading to insignificant adipic acid formation, while the selectivity of adipic acid is 28.5% obtained on the HTS zeolite. Consequently, the higher catalytic performance of the DHBEA zeolite is ascribed to its larger amount of active sites and greater diffusion features than those of HTS zeolite.

Insights into the Reaction Network and Mechanism of Green Aerobic Oxidative Esterification of Methacrolein over Different Heterogeneous Catalysts

The oxidative esterification of methacrolein(MAL)is an important way to prepare high-valued methyl methacrylate(MMA),but this process is ultra-complex due to the high reactivity of both C=O and C=C bonds in MAL molecule.In order to further improve MMA selectivity,the reaction network and relevant mechanisms have been proposed and profoundly investigated in this paper.Five kinds of fundamental reactions are involved in this process,including(a)the acetal reaction;(b)the aerobic oxidation of hemiacetal;(c)the alkoxylation of C=C double bond;(d)the Diels-Alder reaction;and(e)the hydrogenation reaction of unsaturated double bond.Among them,the Diels-Alder reaction of MAL is non-catalyzed,and the Brönsted acid sites or the Lewis acid sites favor promoting acetal reaction of MAL with methanol,while the alkoxylation of C=C bond with methanol is enhanced under alkaline condition.In particular,by employing the Pd-based catalysts,hydrogenation products are formed in alkaline methanol solution,hence with lower than those obtained by the Au-based catalysts.Notably,it is necessary to match the hemiacetal fromation and aerobic oxidation of hemiacetal,which is relevant with the amount and strength of acid and redox sites.Consequently,this work can provide a good guidance for the further design of both catalysts and processes in future.

Identification of Ni_xS_y on Industrial Spent S Zorb Sorbents by Using XPS and TPR-MS

Three industrial spent S Zorb sorbents extracted from production line were studied with XRD, TPR-MS and XPS. The characterization results of XPS and TPR-MS identified the existence of amorphous Ni_xS_y on industrial spent S Zorb sorbents, while the existing XRD quantitative analysis methods can only provide the long-range order in phase information and the grain size of Ni metal. XPS is a powerful tool to investigate the chemical states of nickel atom and the depthwise distribution of nickel species on S Zorb sorbent. Ni_xS_y and Ni metal species coexist on the industrial spent sorbents, and their percentages to total nickel slightly change with the operating conditions in the surface layer. It proves that Ni_xS_y is a stable intermediate product rather than a transition state. The information can contribute to the better elucidation of S Zorb desulfurization mechanism and offer a new direction for selectivity optimization of industrial S Zorb sorbents.

Synthesis of IM-5 Zeolite by Template Pre-Reaction

IM-5 zeolite was synthesized by hydrothermal crystallization method with 1,5-bis(N-methylpyrrolidinium)pentane bromide using the precursors N-methylpyrrolidine and 1,5-dibromopentane as raw materials of template after pre-reaction,and then aluminum,alkali,water and silicon sources were added into the reaction system.The effects of the proportion of precursors and other materials and the reaction conditions on the crystallinity,crystal morphology and pore structure of the synthesized zeolites were systematically investigated,which provided the basic data for industrial production.The physical properties of the synthesized samples were analyzed by XRD,SEM,and N2 adsorptiondesorption techniques,and the catalytic performance of the samples was evaluated.The results show that IM-5 zeolite can be synthesized effectively by using the template pre-reaction method,and its physical properties and catalytic activity in catalytic alkylation of benzene and methanol are comparable to those of industrial samples synthesized by traditional method.

Influences of SiO2/Na2O Molar Ratio on Aging and Chemical Modification of Water Glass

In this paper, the content of water glass before and after adding modifying agent was measured by Trimethylsilyl-gas-chromatography. The experimental results showed that different modulus of water glass could generate different content of mono-silicate acid and oligomeric silicate acid in water glass. After a period of storage, different modulus of water glass led to decrease of silicate content at different levels. Because higher content of Na2O in water glass tended to incur the alkaline polymerization, the occurrence of depolymerization of silicate species would lead to an increase of oligomeric silicate species, resulting in a drawback of silicate species content after a period of storage. And contrary to that, lower content of Na2O in water glass tended to incur the acidic polymerization. When the modifying agent was added to the newly made water glass, the amount of mono-silicate acid and oligomeric silicate acid also decreased. In modified water glass, the change of each silicate acid species was less than that in unmodified water glass. These results showed that the modifying agent retarded the aging of water glass. It had remarkable significance on the theory and practical application of water glass chemistry.

The critical role of Zr in controlling the activity of Pd/Beta on the hydrogenation of phenol to cyclohexanone

The promoting effect of zirconium addition on Pd/Beta catalysts has been investigated in the selective hydrogenation of phenol to cyclohexanone in the aqueous phase. The activity of the catalyst in the reaction was greatly improved by introducing Zr atoms into the framework of H-Beta zeolite. An important synergy between the Zr species and Pd, affecting the Pd dispersion state on the support, has been observed. The modification of the support with Zr^(4+) improves the Lewis/Brφnsted acid ratio of the catalyst, suppressing the further transformation of cyclohexanone. The kinetics of Pd/Zr-Beta catalyst showed high selectivity to cyclohexanone. The catalytic results showed that the Pd/Zr-Beta had the best catalytic performance at the desired temperature of 80℃ for 5 h.

A “Green” Cyclohexanone Oxidation Route Catalyzed by Hollow Titanium Silicate Zeolite for Preparing ε-Caprolactone,6-Hydroxyhexanoic Acid and Adipic Acid

Hollow titanium silicalite (HTS) molecular sieve has been synthesized, and information on its structure, physico-chemical characterization, as well as surface property was investigated by a host of analytical methods, such as XRF, XRD, low-temperature N2 adsorption/desorption, TEM, FT-IR, UV-Vis, 29Si MAS NMR, and XPS techniques. The characterization results suggest that HTS zeolite has a special hollow crystal structure and its mesopore volume is larger than that of TS-1 zeolite. The titanium species in this zeolite are composed of the framework tetrahedral Ti (IV) ions and extra-framework octahedral Ti (IV) ions, which tend to disperse into its bulk phase. This zeolite material also has been applied to catalyze the cyclohexanone oxidation process, and the products are not completely consistent with those results obtained by using TS-1 zeolite, which might be caused by their difference in pore structure and pore volume, especially the mesopore volume. Cyclohexanone oxidation catalyzed by HTS zeolite is a representative consecutive reaction, the main target products of which are e-caprolactone, 6-hydroxyhexanoic acid and adipic acid. The effect of H2O2/cyclohexanone mole ratio on the cyclohexanone conversion, the total target product selectivity, the distribution of three target products selectivity and their variations along with reaction time is also researched and analyzed, which indicate that HTS zeolite shows a high performance for the Baeyer-Villiger reaction of cyclohexanone and catalytic oxidation of 6-hydroxyhexanoic acid under mild conditions, and the quantity of active surface titanium species as well as the pore structure and mesopore volume controlling the mass diffusion rate are the key factors determining the catalytic activity of HTS zeolite and product selectivity.

Study on the Mechanisms for Baeyer-Villiger Oxidation of Cyclohexanone with Hydrogen Peroxide in Different Systems

The green and effective Baeyer-Villiger oxidation reaction of cyclohexanone for preparing ε-caprolactone is of particular importance in the synthesis of new polymer materials. We have discussed here several mechanism types of Baeyer-Villiger oxidation of cyclohexanone with H2O2 in different reaction systems. Five main types have been addressed, i. e.: (1) the non-catalyzed reaction type, where the C=O of ketones is activated by H+, which is electrolytically dissociated from H2O2 and H2O, to improve the capability of C=O group for accepting the electron pairs; (2) the thermally activated radical reaction type, where the Criegee intermediate is produced via two steps of radical reaction with ·OH attack, with much more hydroxyl radicals being excited in the presence of TS-1 zeolite; (3) the Brnsted acid catalysis reaction type, where both O-O moiety and C=O group could be activated by Brnsted acid; (4) the solid Lewis acid catalyzed C=O of the substrate activation reaction type through enhancing the donor-acceptor interaction between the antibonding π*C=O orbital of cyclohexanone and HOMO of Sn-containing zeolites; and (5) the solid Lewis acid catalyzed H2O2 to form Me-OOH oxidative species by converting the highest occupied molecular orbital (HOMO) of Ti-OOH into a singly occupied molecular orbital (SOMO), making the O-O group highly electrophilic to attack the C=O of cyclohexanone during the Baeyer-Villiger oxidation process. In the end, we have also compared the different mechanisms and put forward our opinions on the development direction of catalytic materials aiming at eco-friendly Baeyer-Villiger oxidation of cyclohexanone in the years to come.

Hydrogen peroxide and applications in green hydrocarbon nitridation and oxidation

Basic organic chemicals and high value–added products are mainly produced by hydrocarbon nitridation and oxidation.However,several drawbacks limit the application of the traditional oxidation and nitridation technologies in the future,such as complex processes,poor intrinsic safety,low atom utilization,and serious environmental pollution.The green nitridation and oxidation technologies are urgently needed.Hydrogen peroxide,a well–known green oxidant,is widely used in green hydrocarbon oxidation and nitridation.But its industrial production in China adopts fixed–bed technology,which is fall behind slurry–bed technology adopted by advanced foreign chemical companies,limiting the development of hydrogen peroxide industry and green hydrocarbon nitridation or oxidation industry.This article reviews the industrial production technologies of hydrogen peroxide and basic organic chemicals such as caprolactam,aniline,propene oxide,epichlorohydrin,phenol,and benzenediol,especially introduces the green production technologies of basic organic chemicals related with H_(2)O_(2).The article also emphasis on the efforts of Chinese researchers in developing its own slurry–bed technology of hydrogen peroxide production,and corresponding green hydrocarbon nitridation or oxidation technologies with hydrogen peroxide.Compared with traditional nitridation or oxidation technologies,green production technologies of caprolactam,propene oxide,epichlorohydrin,and benzenediol with hydrogen peroxide promote the nitrogen atom utilization from 60%to near 100%and the carbon atom utilization from 80%to near 100%.The waste emissions and environmental investments are reduced dramatically.Technological blockade against the green chemical industry of China are partially broken down,and technological upgrade in the chemical industry of China is guaranteed.

Regeneration of Simulated Deactivated Hollow Titanium Silicate Zeolite by Secondary Crystallization in the TPAOH Solution

It is of paramount importance to improve the utilization efficiency of hollow titanium silicate(HTS) zeolite catalyst used in the cyclohexanone ammoxidation process. To achieve this aim, the regeneration of simulated deactivated HTS zeolite by post-synthesis was carried out in an aqueous TPAOH solution under hydrothermal conditions. It was found that the catalytic performance for phenol hydroxylation over regenerated HTS zeolite was as high as that of fresh one.Judging from the BET measurements, electron micrography and XRD analysis results, it was confirmed that the topological and morphological structure was repaired. The chemical state of Ti species was detected by the UV-Vis and ^(29)Si MAS NMR spectroscopy. No acidic amorphous TiO_2-SiO_2 oxide was formed, and the extraframework Ti species could be reincorporated into the framework of HTS zeolite thanks to the tetrahedral coordination by the condensation between Ti-OH and Si-OH groups. In order to confirm this conclusion, the fresh HTS zeolite was treated under the NH_3·H_2O hydrothermal and thermal conditions for several times. The catalytic activity of both uncalcined and calcined simulated deactivated HTS zeolite samples could be regenerated without the formation of Br?nsted acid sites. It was concluded that the highly dispersed Ti species could be reincorporated into the framework of zeolite by hydrated condensation of Si-OH and Ti-OH groups after secondary hydrothermal synthesis.

Deactivation Behavior of Hollow Titanium Silicalite Zeolite in Aqueous Ammonia Solution under Simulated Industrial Cyclohexanone Ammoximation Conditions

For simulating the real deactivation of hollow titanium silicalite(HTS) zeolite in commercial ammoximation process, HTS was treated by 10% NH_3·H_2O solution at 120 ℃ in stirred autoclave. It is found that a part of HTS zeolite crystals dissolved in the hot NH_3·H_2O solution, and the specific surface area and pore volume continuously decreased with the increase in NH_3 hydrothermal treatment time. Meanwhile, the transformation of framework Ti species into extraframework Ti species was detected by the spectroscopic methods. However, the extraframework Ti species were still in a highly dispersed state after the hydrothermal and thermal treatments as shown by TEM images, while the formation of new acid sites was not detected. Upon combining the results of characterization with catalytic performance of HTS, the main deactivation reason for this material had been determined, which might be attributed to the reduction of specific surface area and active centers after basic treatment and calcination of HTS samples. And then the possible mechanism of simulated deactivation of HTS zeolite was proposed, which could describe the elemental reaction steps much more visually and directly.

Investigation on Organic Solvent Free Toluene Oxidative Bromination Reaction Catalyzed by HTS Zeolite

The toluene oxidative bromination reaction catalyzed by hollow titanium silicalite(HTS)zeolite in aqueous medium was investigated by employing H2O2 and HBr under mild conditions without the need for organic solvent.A high toluene conversion(90.7%)and high selectivity of mono-bromotoluene(99.0%)was achieved under the optimal reaction conditions.The UV-Raman spectroscopy was applied for the mechanism study and the result reveals that HTS is efficient for catalyzing the oxidation reaction of HBr with H2O2 to produce abundant active bromine species,which can further facilitate the toluene electrophilic bromination reaction.A two-step toluene bromination reaction mechanism involving the HTS catalyzed active bromine species“generation-conversion-utilization”process is proposed based on the UV-Raman spectroscopy analysis.

Effects of Recrystallization Parameters on the Formation of Hollow Silicalite-1 Zeolite

Hollow silicalite-1 zeolite can be readily fabricated by hydrothermally treating the parent silicalite-1 with tetrapropylammonium hydroxide. A dissolution-recrystallization mechanism has been previously proposed to explain the formation of such hollow structures, but detailed information of this formation process still remains unclear. Herein, by tracking the evolvement of the hollow voids and morphology of the silicalite-1 under various treatments using XRD, SEM, TEM and N2 adsorption/desorption techniques, we systematically studied the formation process of the hollow structure of silicalite-1 zeolite and discovered that the organic template, water, treating temperature and time can significantly influence the morphology and size of hollow structure inside silicalite-1 zeolite crystals. Generally, a diluted synthesis medium with high template content under suitable temperature(for instance 170 °C) and extended treatment time favors the formation of single hexagonal hollow structure within silicalite-1 zeolites;while other conditions favor the formation of rounded hollow voids or even multiple-voids within silicalite-1 zeolites.

Effect of Zeolite 5A Particle Size on Its Performance for Adsorptive Separation of Ethylene/Ethane

The adsorptive separation of ethylene from ethane exhibits a less energy-intensive-alternative technique with development potential among all processes for separation of ethylene/ethane currently. In this approach, zeolite 5 A with different particle sizes ranging from 3 340 nm to 440 nm was prepared by hydrothermal synthesis. The effect of particle size on the adsorptive separation performance of zeolite 5 A was investigated. The results show that the particle size has a significant effect on the ethylene IAST(Ideal Adsorbed Solution Theory) selectivity of zeolite 5 A. The zeolite 5 A with a particle size of 710 nm demonstrated the highest ethylene selectivity(5.6). The relatively high crystallinity of zeolite 5 A is in favor of massive adsorption capacities of ethylene and ethane.

One-pot Synthesis of 6-Hydroxyhexanoic Acid from Cyclohexanone Catalyzed by Dealuminated HBEA Zeolite with Aqueous 30% H_2O_2 Solution

The one-pot synthesis of 6-hydroxyhexanoic acid from cyclohexanone via the integrated Baeyer-Villiger oxidation and ring opening reaction catalyzed by dealuminated HBEA zeolite has been developed. Under optimized conditions, the cyclohexanone conversion and 6-hydroxyhexanoic acid selectivity are over 95%, respectively. The excellent catalytic performance is attributed to the activation of carbonyl group of cyclohexanone and the fast hydrolysis and ring opening of ε-caprolactone by both Lewis acid and Br?nsted acid sites under aqueous conditions.

Post-synthesis and structural evolution of hollow titanium silicalite-1 with solvent-free method

Generating hollow structure inside titanium silicalite-1(TS-1)is a widely used method to improve its liquid-phase oxidation catalytic performance in industry.However,traditional dissolution-recrystallization method usually required a large amount of aqueous solution of organic template,leading to unfavorable polluted waste,low production efficiency,and high manufacture cost.Here,a facile and environmental friendly strategy was proposed for the post-synthesis of hollow TS-1 zeolite with a solventfree method utilizing NH4HCO3 and tetrapropylammounium bromide as selective etching agents,which reduced the usage of organic template and avoided the liquid waste.The high crystallinity,the microporous structure,and the active Ti sites were preserved at a high product yield(>93%).The formation mechanism of hollow structure was also investigated by exploring effects of different reactants and experimental parameters.Meanwhile,the obtained hollow TS-1 showed an outstanding performance in the epoxidation of 1-hexene in comparison to the parent zeolite.

Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement

Developing efficient and stable zeolites for vapor-phase Beckmann rearrangement of cyclohexanone oxime is still a great challenge to realizeε-caprolactam(CPL)green production.In this work,the hierarchical porous silicalite-1 zeolites with multiple hollow structure(S-1-M)are explored by in-situ desilication−recrystallization post-treatment of spongy highway-like zeolites(S-1-S),which are synthesized through silanization synthesis of conventional bulky silicalite-1(S-1).Compared to S-1,S-1-M achieves superior catalytic performance,with improving the CPL selectivity from 85.7%to 94.1%and prolonging the catalyst lifetime from 74 to 126 h at a weight hourly space velocity(WHSV)of 6 h^(−1).Comprehensive physiochemical studies demonstrate that the highly dispersed intracrystalline cavities within S-1-M endow greater mass diffusion and better quasi acidity inducing by the enhanced H-bonds among abundant H-bonded silanols,which is cooperatively responsible for its superior catalytic performance.

A nickel-iron layered double hydroxide-supported Au catalyst for efficient electrocatalytic C-C coupling reaction coupled with H_(2) production

Coupling of cathodic H_(2) production with electrosynthesis of organic compounds not only solves the problem of sluggish oxygen evolution reaction(OER) kinetics, but also produces valuable chemicals. However, this strategy has rarely been explored for direct and selective C(sp~3)-H activation to construct C-C bonds, which could significantly enhance the synthetic efficiency in organic synthesis. Here, we report a nickel-iron layered double hydroxide-supported gold catalyst(Au/NiFe-LDH) for efficient electrocatalytic C-C coupling reaction in direct C(sp~3)-H alkynylation of tertiary aliphatic amines with 1-iodoalkynes, which is coupled with H_(2) production. Specifically, triethylamine and 1-iodoalkynes undergo efficient alkynylation to afford propargylamine in high yield(79%) and recycling ability without addition of external oxidants, coupling with 78-fold higher H_(2) productivity compared with water splitting under the same potential. This work may shed light on OER-substituted reaction towards C-C bond formation reactions under mild conditions.

Extension of Highly Efficient Alcohol-promoted Rearrangement into One-pot Domino Palladium-catalyzed Carbonylation for Sterically Crowded Aromatic Six-membered Imides

Aromatic six-membered imides suffer the introduction of bulky substituents at the imide positions due to the formation of isoimides and low reactivity,preventing from the investigation of the intrinsic molecular properties.Here,we found a highly efficient alcohol-promoted rearrangement from isonaphthalimide to naphthalimide under acid or basic nonaqueous conditions,which can be regarded as model compounds for aromatic six-membered imides.We proposed two-step nucleophilic substitutions in the isomerization mechanistic pathways that were verified by the separation of a key intermediate.Furthermore,in-situ ^(1)H NMR exhibited the first-order kinetics for the isoimide loss process.Finally,the alcohol-promoted isoimide-imide rearrangement was extended to a palladium-catalyzed one-pot domino carbonylation reaction toward sterically crowded aromatic six-membered imides.