Tetrapropylammonium Hydroxide Solution Research Articles

Catalytic oxidation of toluene using layer-modified Mn-Ce solid solution with high specific surface area

Numerous studies have been reported on the application of Mn-Ce catalysts for the catalytic oxidation of toluene, and the modification of their physical structure has become an important method to favour toluene adsorption. This paper modified (MnCe)Ox by using a series of organic solutions. The catalysts modified by different organic solutions were prepared for the catalytic oxidation of toluene by impregnation method with calcination at 500 °C. Activity test results showed that the MC-TPAOH catalyst modified by tetrapropylammonium hydroxide solution had the best catalytic performance, with T50 and T90 of 192 °C and 221 °C. The MnO2 species on the surface of the catalyst modified by the organic solution were in an amorphous state, and the solid-solution effect of Mn-Ce was enhanced. Tetrapropylammonium hydroxide has greater solubility in polar solvents due to its higher number of C atoms and exhibits stronger phase-transfer ability, which was favourable to the Mn-Ce interaction. The structural properties of the catalyst were modulated by lamellar modification, which increased the specific surface area and formed a porous structure. The redox capacity was greatly improved, and more oxygen vacancies were exposed on the surface, which was conducive to the migration of active oxygen species. Reactive oxygen species present on the catalyst surface were the basis for its excellent activity. This study modifies (MnCe)Ox by organic solution to avoid the introduction of impurity ions. It opens a new direction for the physical structure modulation of Mn-Ce composite oxides and lays a research foundation for the organic modification of Mn-Ce composite oxides.

Трансформация изопропанола с использованием гибридных цеолитсодержащих систем типа H-ZSM-5 и H-Beta

The continuous depletion of hydrocarbon sources contributes to a wide study of the use of biorenewable raw materials to obtain synthetic hydrocarbons from them. Isopropyl alcohol is traditionally produced by chemical hydration of propylene, however, with the development of biotechnology, broad prospects have opened for its production by fermentation of glucose-containing substrates obtained from agricultural and forestry waste. This way, isopropyl alcohol can also be considered as a bio-renewable raw material and it can be widely used for the production of chemical synthesis products, including hydrocarbons. One of the possible ways of processing isopropyl alcohol is the catalytic transformation of alcohols on zeolites and zeotypes of various natures with the formation of hydrocarbons. Currently, zeolite H-ZSM-5 and zeotype SAPO-34 are the most frequently used catalysts for the transformation of alcohols into hydrocarbons, however, their rapid deactivation due to the formation of a carbon residue remains an unresolved problem. The formation of core-shell structures with H-ZSM-5 zeolite in center and an outer shell consist of H-Beta zeolite with large pores can reduce the deactivation of zeolite because of increase in reagents diffusion rate. In this article is devoted to synthesis of ZSM-5/Beta sample with a core-shell structure, as well as a study of its catalytic and physicochemical properties. To form the H-ZSM-5 zeolite, a colloidal solution of tetrapropylammonium hydroxide, a colloidal solution of silicon oxide, aluminum oxide, sodium hydroxide of distilled water was used. The colloidal solution was placed in an autoclave, heated to 140 °C and kept at this temperature for 48 hours, after which the crystals formed were centrifuged, washed with distilled water and kept in a 1M solution of ammonium nitrate for a day. Then, to form the H-Beta layer, H-ZSM-5 was suspended in a colloidal solution consisting of tetraethylammonium hydroxide, tetraethylammonium chloride, a colloidal solution of silicon oxide, sodium hydroxide, sodium chloride and distilled water. The suspension was placed in an autoclave and kept at a temperature of 140 °C for 48 hours, followed by centrifugation, washing in distilled water, suspended in a 1M solution of ammonium nitrate, with repeated washing with distilled water, drying and calcining at 600 °C. Testing of the synthesized of H-ZSM-5/Beta zeolite sample showed a significant decrease in the rate of deactivation compared to the synthesized sample of H-ZSM-5; it is also necessary to note a slight increase in the fraction of liquid hydrocarbons for the sample H-ZSM-5/Beta.

Anionic Tuning of Zeolite Crystallization

Zeolites are of great industrial relevance as catalysts, adsorbents, and ion-exchangers and typically synthesized under hydrothermal conditions. Rational regulation of their crystallization process...

Development of mesoporous ZSM-5 zeolite with microporosity preservation through induced desilication

Alkali treatment is a widely used strategy to create mesopores for microporous zeolites to decrease the diffusion limitation in micropores. However, many of the micropore losses existed due to the uncontrollable destruction of framework. In this paper, a series of mesoporous ZSM-5 with well-maintained micropores was synthesized through induced desilication strategy. To induce the diffusion of alkali solution for the homogenizing desilication and mesopore formation, abundant and uniform small mesopores were firstly built for ZSM-5 by protective desilication in tetrapropylammonium hydroxide solution. The pore structure and acidity of the obtained ZSM-5 were characterized by XRD, TEM, N2 physisorption, NH3-TPD and Py-IR. Through induced desilication, the external surface area of obtained ZSM-5 increased from 42 m2 g−1 of parent ZSM-5 to 148 m2 g−1 and only 17% of micropore surface area was sacrificed, which was far lower than 37% of the loss in traditional NaOH treatment. Meanwhile, the strong acid sites were well preserved and the external acid sites were reduced. Compared with the sample treated by NaOH solution, the obtained catalyst exhibited higher catalytic stability and aromatics, especially PX selectivity. Good regenerated performance with long catalytic lifetime and high liquid hydrocarbon yield could also be found for the obtained catalyst. The strategy proposed in this paper is simple and ingenious in tailoring the porosity since it only relies on the desilication method, which is different from the usual coupling of dealumination and desilication.

Synthesis Strategy of Hierarchical Alumiosilicates from Low Grade Indonesian Kaolin with Adjusted Activity in Acetalization Reaction

Synthesis strategy of hierarchical aluminosilicates was carried out by varying the starting material, type of a basic solution, and the hydrothermal condition. Aluminosilicate was synthesized using pre-treated low-quality kaolin by three kinds of basic solution, such as sodium hydroxide, sodium fluoride, and tetrapropyl ammonium hydroxide. The hydrothermal condition was carried out by gradual temperature and constant temperature. The desired mole ratio of Si/Al achieved by dealumination or by addition of silica. Products were characterized by X-ray diffraction, FTIR spectrometry, and nitrogen physisorption. Cation exchange was carried out on the product to obtain an acid catalyst. The acidity test of the catalyst was carried out by FTIR-pyridine spectrometry. The catalyst activity test was carried out to the acetalization reaction of 3,4-dimethoxybenzaldehyde with propylene glycol. The results showed that the catalyst synthesized with the basic solution of tetrapropyl ammonium hydroxide had the highest acid site number and the highest conversion of 3,4-dimethoxybenzaldehyde to acetal.

A strategy for fast and facile embedding platinum nanoparticles in silicalite‑1 crystallites with a stable and catalytic active structure

A strategy for embedding ultrasmall Pt nanoparticles in silicalite-1 (S-1) was proposed. It consists of treating the zeolite with tetrapropylammonium hydroxide (TPAOH) solution, loading Pt, and recrystallizing the resultant composite in a silicon-containing Na+-free TPAOH solution at 170 °C for 6 h. Complementary characterizations confirm that, the first step is facile and effective for creating plenty of mesopores in the zeolite, and the last step is fast and favorable for embedding ultrasmall Pt nanoparticles in S-1 yielding the Pt@S-1 hybrid. This material displayed excellent resistance to sintering and much higher activity for ethylene hydrogenation and CO oxidation than conventional Pt-loading catalyst.

In-depth understanding the role of seeds in the synthesis of TS-1

The role of the seed in the seed-induced synthesis of TS-1 zeolite process was investigated in detail. The results revealed that the seed not only reduced the crystal size as reported previously but also promoted the incorporation of titanium atoms into the framework of TS-1 zeolite. Systematic investigations of the depolymerization behavior of TS-1 seeds in the tetrapropylammonium hydroxide (TPAOH) solution showed that the particle size and amount of TS-1 seeds directly affected the degree of depolymerization. Interestingly, the obtained TS-1 also had a similar catalytic performance when the completely-depolymerized seed species instead of seed crystals were added to the synthesis system. Meanwhile, the XRD pattern and IR spectra results showed that there were not any MFI framework units in completely-depolymerized seed species. Consequently, the effective ingredient of seeds was the species that had been depolymerized in the TPAOH solution.

Steam cracking of green diesel (C12) to BTX and olefins over silane-treated hierarchical BEA

Commercial BEA zeolite was modified under the radiation of microwave labstation with different modification strategies. Catalytic properties and textural properties were manipulated by desilication using sodium hydroxide or tetrapropyl ammonium hydroxide solution. It was found that sodium hydroxide can lead to very fragile textural properties and low catalytic activity. While tetrapropyl ammonium hydroxide is highly recommended for the improvement of textural properties, especially at long desilication time. Parent and desilicated samples were further modified by octadecyltrichlorosilane (OTS) in order to add the silane functionality to the zeolitic materials. This addition led to minimizing the textural properties of the silane-treated BEA zeolites and consequentially led to a reduction in the catalytic activity. Recovering and improving the catalytic activity and textural properties were then performed by calcining the silane-treated catalyst to combust the long-chain alkyl groups, which facilitate the formation of silica layer. Another modification strategy was found that the desilicated BEA sample can enhance the catalytic activity and catalytic stability when it treated with a low concentration of nitric acid after desilication. This modification strategy led to improving the catalytic conversion from 29% to 76%.

Effect of alkali-treated HZSM-5 zeolite on the production of aromatic hydrocarbons from microwave assisted catalytic fast pyrolysis (MACFP) of rice husk

We performed microwave-assisted catalytic fast pyrolysis (MACFP) of rice husk (RH) over an alkali-treated HZSM-5 zeolite, for production of hydrocarbons. The treatment consisted in the modification of the HZSM-5 by the organic base tetrapropylammonium hydroxide (TPAOH) solution at several concentrations. We characterized the resulting catalysts by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption, and temperature-programmed sorption of ammonia (NH3-TPD). The results suggest that the TPAOH treatment generated mesoporous structures in the HZSM-5, while preserving its microporous structure and crystallinity. We obtained the highest yield (45.9%) of hydrocarbons from MACFP of rice husk (RH) at 550 °C. As the TPAOH concentration increases, the relative content of BTEX hydrocarbons (benzene, toluene, ethylbenzene, and xylene) reaches a maximum value of 22.9% at 2.0 mol/L. A comparison of results obtained over the organic base TPAOH (HZSM-5 modified by 2.0 mol/L TPAOH solution) with those obtained over an inorganic base (HZSM-5 modified by 2.0 mol/L NaOH solution) shows a 4.3% increase in the relative content of monocyclic aromatic hydrocarbons for the TPAOH. In addition, the TPAOH-treated catalyst shows excellent selectivity of BTEX (58.5%), which is higher than the selectivity obtained with the parent HZSM-5 (51.2%) and NaOH-treated HZSM-5 (53.9%). The TPAOH-modified HZSM-5 catalyst effectively reduced coke formation by 4.6% compared to MACFP over the parent HZSM-5, most likely because TPAOH decreases the concentration of strong acidic sites on the outer surface of the catalyst, creating a mesoporous structure while retaining the weak acidic sites on the HZSM-5 inner surface. The new catalyst generated in this work contains a moderate amount of mesopores structures, which allows for effective upgrading of pyrolysis vapors while simultaneously reducing coke formation, thereby addressing a significant problem in the development of the catalytic fast pyrolysis process.

Highly dispersed Pt nanoparticles confined within hierarchical pores of silicalite-1 zeolite via crystal transformation of supported Pt/S-1 catalyst for partial oxidation of methane to syngas

Highly dispersed Pt nanoparticles confined within hierarchical pores of silicalite-1 zeolite were prepared via crystal transformation of supported Pt/S-1 catalyst. Selective dissolution and external recrystallization in tetrapropylammonium hydroxide solution enabled metal nanoparticles to be encapsulated in zeolites. The abundant pore structures of as-prepared Pt@S-1 catalyst were obtained by properly controlling the time of desilication and recrystallization. The properties of Pt@S-1 catalyst with hierarchical pores were characterized by XRD, ICP, SEM, TEM/HRTEM, N2/Ar adsorption-desorption, CO adsorption, H2-TPR and TGA techniques. Compared with the traditional supported Pt/S-1 catalyst, Pt@S-1 catalyst exhibited excellent sintering resistance, owing to the restriction of the recrystallized shell. Further, abundant pore provided access to contact with the active components, the Pt@S-1 catalyst showed excellently catalytic performance. CH4 conversion and product selectivity were significantly improved. The out-standing catalytic performance was attributed to recrystallization of silica supported Pt. The strategy afforded enriched pore structure, improved the dispersion of active metal, and reduced the size of Pt nanoparticles. In addition, hierarchical pores of silicalite-1 zeolite supports also contributed to shorten the diffusion path of reactions.

Post-synthesis Treatment of TS-1 with TPAOH: Effect of Hydrophobicity on the Liquid-Phase Oxidation of Furfural to Maleic Acid

A series of modified TS-1 catalysts was prepared by post-synthesis hydrothermal treatment of a parent TS-1 zeolite with solutions of different concentrations of tetrapropylammonium hydroxide (TPAOH). The treatment results in an advantageous improvement of the catalytic activity for the liquid oxidation of furfural with H2O2 to produce maleic acid. The highest yield of maleic acid (83%) was obtained when using 0.025 M TPAOH solution; while the maximum yield of the untreated TS-1 was 70%. The catalysts were thoroughly characterised by XRD, UV–Vis, ICP–OES, XPS, TEM, N2-adsorption, DRIFT of chemisorbed deuterated acetonitrile and TEM, in order to elucidate the origin of the catalytic improvement. The characterisation studies allowed us to conclude that, besides the well-known creation of mesopores within the zeolite primary particles, the TPAOH treatment also results in the increase of the hydrophobicity balance of the channels and cavities of the zeolites (via silanols removal). Both properties have a relevant effect on the improvement of the catalytic properties.

Synthesis of Hierarchical Titanium‐Rich Titanium Silicalite‐1 Zeolites and the Highly Efficient Catalytic Performance for Hydroxylation of Phenol

AbstractImproving the framework titanium (Ti) of titanium silicalite‐1 (TS‐1) zeolites and creating inter‐crystalline mesoporosity are two ways to enhance the catalytic properties of TS‐1 for hydroxylation of phenol. Most researches only used one of the ways. In this study, we successfully synthesized of hierarchical Titanium‐Rich (Ti‐rich) TS‐1. Ti‐rich TS‐1 was synthesized in the presence of ammonium carbonate ((NH4)2CO3). The framework Ti content of TS‐1 zeolites synthesized by different content of (NH4)2CO3 was studied by X‐ray fluorescence (XRF), Fourier transform infrared spectra (FTIR) and ultraviolet visible spectra, the framework Ti content was significantly increased by using (NH4)2CO3 as crystallization‐mediating agent. The synthesized samples were evaluated in hydroxylation of phenol. When the molar ratio of ammonium carbonate and tetraethyl orthosilicate in the synthesis gel was 0.2, the molar ratio of Si/Ti reached 34.43 and the Ti‐rich TS‐1 shows the optimum catalytic activity in hydroxylation of phenol. The post‐modification with aqueous solution of tetrapropylammonium hydroxide (TPAOH) was used to further improve the diffusion property. Compared with the parent TS‐1, the secondary pore volume was all increased. The developed hierarchical Ti‐rich TS‐1 zeolites were also assessed in hydroxylation of phenol. It was confirmed that hierarchical Ti‐rich titanium silicalite‐1 zeolites can improve the catalytic activity in phenol conversion considerably.

Density Measurement of Aqueous solution of Tetrapropylammonium Hydroxide at different Temperatures and Concentrations: Data and Correlation

Densities of aqueous Tetrapropylammonium hydroxide solution (5,10, 15, 20 and 25 wt %) were invistigated over a temperature range of 298.15 to 333.15 K and at atmospheric pressure. Derived properties, molar volume (Vm) and excess molar volumes were estimated and correlated with temperature using the least square method. The predicted values from correlations are in good agreement with measured values. The obtained results from derived properties for a binary system, are interpreted based on intermolecular interactions.

Hierarchical Shell-Like ZSM-5 with Tunable Porosity Synthesized by using a Dissolution-Recrystallization Approach.

Zeolites have been widely used in various fields in industry, such as catalysis, separation, and adsorption, etc. The small pore size of the micropores in the zeolite could lead to severe diffusion resistance in mass transfer. Numerous efforts have been dedicated to imposing hierarchical pore systems into zeolites by using templates or leaching methods. Here, we report the synthesis of single-crystalline hierarchical shell-like ZSM-5 by utilizing a dissolution-recrystallization post-treatment on mesoporous ZSM-5. Tetrapropylammonium hydroxide solution was used in the post-treatment. The hierarchical porosity in the crystalline shell can be controlled by adding sodium cations into the synthesis system. The hierarchical shell-like ZSM-5 reported here shows higher catalytic activity in acetalization reactions containing bulky molecules.

Post-treatment of TS-1 with Mixtures of TPAOH and Ammonium Salts and the Catalytic Properties in Propylene Epoxidation

TS-1/SiO2 extrudate was post-treated with mixed solution of tetrapropyl ammonium hydroxide (TPAOH) and various ammonium salts solution (NH4F, (NH4)3PO4, (NH4)2CO3, (NH4)2SO4, NH4CH3CO2, NH4NO3, NH4Cl and (NH4)2TiF6). The obtained hierarchical TS-1 catalysts were characterized by many techniques and tested for propylene epoxidation using hydrogen peroxide as an oxidant in a fixed-bed reactor. It was shown that the physicochemical and catalytic properties of the treated TS-1/SiO2 extrudate depended on the types of ammonium salts added. Compared to the treatment with TPAOH alone, the treatment with a mixed solution of TPAOH and some ammonium salts can greatly improve the catalytic properties of the treated TS-1/SiO2 extrudate. Some of these ammonium salts were favorable for the incorporation of titanium in the framework, and the beneficial effect depended on the types of ammonium salt. TS-1/SiO2 extrudate treated with a mixed solution of TPAOH and (NH4)3PO4 exhibited the highest catalyst stability in propylene epoxidation. Such catalytic property can be correlated to high crystallinity, more framework titanium, large specific surface area and large external surface area.

The High-Performance Hollow Silicalite-1@Titanium Silicalite-1 Core-Shell Catalyst for Propene Epoxidation

Hollow silicalite-1@titanium silicalite-1 (H−S-1@TS-1) core-shell catalyst was synthesized in hydrothermal system with hollow silicalite-1 serving as core. In this novel method, tetrapropylammonium hydroxide (TPAOH) served as the single template in the whole synthesis process so as to avoid secondary structure directing agents (SDAs) that traditional methods applied to give core-shell TS-1. Since inner hollow structure was given by S-1, H−S-1@TS-1 avoided framework Ti leaching in coventional dissolution-recrystallization process that gave hollow TS-1 and thus it was in absence of extra-framework Ti. H−S-1@TS-1 showed better propene epoxidation activity (TOF=13.61 mol (mol h)−1) than microporous TS-1 (TOF=8.08 mol (mol h)−1) and micro-TS-1 post-treated with TPAOH solution (TOF=9.75 mol (mol h)−1) due to the synergy function of pure framework Ti species, higher surface Ti content and enhanced diffusion property.

Fabrication of Hollow Mesoporous Nanosized ZSM‐5 Catalyst with Superior Methanol‐to‐Hydrocarbons Performance by Controllable Desilication

AbstractThis work aims to improve the catalyst lifetime of ZSM‐5 for the methanol‐to‐hydrocarbons conversion by tuning the pore structure and external surface area on nano‐ZSM‐5 (100 nm). Several differently pore‐structured samples were synthesized based on the controllable desilication of nano‐ZSM‐5 by prolonging the alkali‐treatment time and introducing tetrapropylammonium hydroxide (TPAOH) into NaOH solution. 2 h NaOH treatment produced mesoporous ZSM‐5 with well‐maintained interior, and the catalytic lifetime was prolonged from 60 to 127 h along with increased isoparaffins selectivity owing to improved diffusion and accessibility of internal weak acid sites. If prolonging the treating time to 15 h, nano‐ZSM‐5 with initially formed hollow structure (HI‐Z5) was achieved, which shows relatively short lifetime of 85 h and high aromatics selectivity. After a secondary treatment of HI‐Z5 with fresh NaOH solution for 5 h, the formed thin shell and clean interior significantly improved diffusion, and the lifetime increased from 85 to 115 h. The aromatics selectivity was also increased by the enhanced acidity. Mesopores were introduced into the shell of HI‐Z5 after treating it with a freshly mixed solution of NaOH and TPAOH. The external surface area exhibited a 94 % increase, resulting in a high isoparaffins selectivity and a long lifetime of 149 h.

Enhanced Catalytic Activity on Post‐Synthesized Hollow Titanium Silicalite‐1 with High Titanium Content on the External Surface

AbstractA titanium silicalite‐1 (TS‐1) extrudate with high content of titanium on the external surface was post‐synthesized by using the mixed solution of tetrapropylammonium hydroxide and the hydrolysate of tetrabutyl titanate. The influence of Ti concentration in the post‐synthesis solution on the physicochemical properties and catalytic performance of TS‐1 was also studied. The amorphous silica support covering on the external surface of TS‐1 was crystallized, and some hollows appeared in the samples that were post‐synthesized. Most titanium introduced by this method are located at the external surface of the new generated TS‐1 particles. The molar ratio of Si/Ti on the external surface decreases with the increase of the Ti concentration in the post‐synthesis solution. The catalytic activity for phenol hydroxylation over the TS‐1 samples is enhanced after the post‐synthesis due to the new generated framework Ti on the external surface, providing the reactants more easily adsorbable active centers. A proper Ti concentration (10 vol%) in the post‐synthesis solution leads to the highest catalytic activity by obtaining a proper ratio of tetrahedral and octahedral Ti to anatase TiO2.

Hollow ZSM‐5 with Silicon‐Rich Surface, Double Shells, and Functionalized Interior with Metallic Nanoparticles and Carbon Nanotubes

Hollow ZSM‐5 single crystals with silicon‐rich exterior surface are prepared by a “dissolution–recrystallization” strategy in tetrapropylammonium hydroxide solution. Selective dissolution and exterior recrystallization cause the silicon components to migrate from the inside to outside, resulting in a regular void in the interior of the crystal, increased Brönsted acid sites and a silicon‐rich external surface. The as‐prepared hollow ZSM‐5 exhibits excellent acid catalysis with enhanced shape selectivity, as shown in biphenyl methylation as a probe reaction, which is attributed to the silicon‐rich external surface and thus the inhibition of isomerization on external surface. More interestingly, hollow ZSM‐5 single crystals with double shells are successfully prepared by layer‐by‐layer technique followed with dissolution–recrystallization strategy. Furthermore, hollow ZSM‐5 encapsulating iron and carbon nanotubes are successfully synthesized. Furthermore, hollow ZSM‐5 nanosized crystals with the interior functionalized as bimetallic (oxide) nanoparticles such as CuO‐Pd are also successfully synthesized.

Transformation of SiO2 in Titanium Silicalite-1/SiO2 extrudates during tetrapropylammonium hydroxide treatment and improvement of catalytic properties for propylene epoxidation

Abstract Titanium Silicalite-1 (TS-1)/SiO2 extrudates were treated with tetrapropylammonium hydroxide (TPAOH) solutions under hydrothermal conditions. The catalysts were characterized using various analysis techniques including X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis), UV Raman, X-ray photoelectron spectroscopy (XPS), nitrogen physisorption, X-ray fluorescence (XRF), 29Si magic-angle-spinning nuclear magnetic resonance (29Si MAS NMR) spectroscopy, and transmission electron microscopy (TEM). The transformation of amorphous SiO2 in TS-1/SiO2 catalysts during TPAOH treatment was studied in detail. The results show that the SiO2 dissolved and then crystallized during TPAOH treatment, which increased the hydrophobicity and the ratio of Si/Ti on the external surface of TS-1. Moreover, the existence of SiO2 inhibited the formation of anatase TiO2 during TPAOH treatment. The changes in physical and chemical properties not only improved the catalytic activity but also improved the stability of catalysts after TPAOH treatment. The experimental results show that the treated TS-1/SiO2 catalysts exhibited higher catalytic activity and stability than the untreated counterparts. Especially for the TS-1/SiO2 catalyst treated with 0.06 mol/L TPAOH solution for 72 h, the H2O2 conversion still remained above 90% and the propylene oxide selectivity was as high as 99% after a long-term run with time on stream (TOS) of 648 h.