Good Hydrothermal Stability Research Articles

Simultaneously Enhanced Hydrophilicity and Stability of a Metal‐Organic Framework via Post‐Synthetic Modification for Water Vapor Sorption/Desorption

AbstractWith increasing demands for high‐performance water sorption materials, metal‐organic frameworks (MOFs) have gained considerable attention due to their high maximum uptake capacities. In many cases, however, high overall capacity is not necessarily accomplishing high working capacity under operating conditions, due to insufficient hydrophilicity and/or water stability. Herein, we present a post‐synthetic modification (PSM) of MOF‐808, with di‐sulfonic acids enhancing simultaneously its hydrophilicity and water stability without sacrificing its uptake capacity of ≈30 mmol g−1. Di‐sulfonic acid PSM enabled a shift of the relative humidity (RH) associated with a sharp step in water vapor sorption from 35–40 % RH in MOF‐808 to below 25 % RH. While MOF‐808 lost uptake capacity and crystallinity over multiple sorption/desorption cycles, the di‐sulfonic acid PSM MOF‐808 retained >80 % of the original capacity. PSM MOF‐808 exhibited good hydrothermal stability up to 60 °C and high swing capacity.

Titanium Phosphate Grafted on Mesoporous SBA-15 Silica as a Solid Acid Catalyst for the Synthesis of 5-Hydroxymethylfurfural from Glucose

The grafting of titania on SBA-15 followed by its phosphation was presented to prepare a mesoporous Lewis–Brønsted bifunctional solid acid catalyst for the tandem conversion of glucose via fructose to 5-hydroxymethylfurfural (HMF). Titania was dispersed on SBA-15 as an amorphous surface layer containing abundant coordinatively unsaturated tetrahedral Ti ions, which was reactive and readily transformed upon phosphation into a new titanium phosphate phase with the chemical formula identified as Ti2O3(H2PO4)2·2H2O. The ordered mesoporous structure was well maintained after three modification cycles, affording a desirable surface area of over 300 m2/g. The SBA-15-supported titanium phosphate layer affords higher overall acidity and Brønsted to Lewis acid ratio, compared with the conventional post-phosphated bulk anatase titania. The tetrahedral Ti ions and the adjacent protonated phosphate groups on the titanium phosphate layer could form Lewis–Brønsted acid pairs at molecular level proximity, which largely enhanced the selective tandem catalysis for glucose conversion via fructose to HMF. An optimized HMF yield of 71% was achieved at 160 °C in a water–methyltetrahydrofuran biphasic system over the SBA-15-supported titanium phosphate catalyst. The catalyst exhibited good hydrothermal stability with a rather limited silicon and phosphate leaching, and no distinct pore collapse or performance loss over three sequential reaction runs.

Zeolite-Containing Catalysts in Alkylation Processes

This article provides an overview of zeolite-containing catalysts used in the alkylation of benzene and toluene with olefins, isobutane with butenes and butane-butene fractions, gasoline and oil fractions with olefins, propane-propylene, and butane-butylene fractions of catalytic cracking. Zeolites have various types of structures, including BEA, MFI, MWW, FAU, etc., which differ in pore size and the number and location of the channels. High-silica zeolites have a large pore volume, high acidity, good hydrothermal stability, and molecular sieve properties that provide high selectivity in alkylation processes.

Synthesis of Hierarchical TS-1 and Its Recycling Catalytic Property for Oxidative Desulfurization

Because of its unique pore structure, good hydrothermal stability and high specific surface area, hierarchical TS-1 zeolite (HTS-1) has become an important catalyst for the deep oxidative desulfurization of fuel oils. In this work, HTS-1 has been successfully synthesized by a hydrothermal crystallization method using the C-SiO2 composite as both silicon source and mesoporous template, tetrapropylammonium hydroxide as microporous template, and tetrabutylorthotitanate as titanium source. The C-SiO2 composite is obtained by mild carbonization of the SiO2/T-40 (Tween 40) xerogel, which is prepared by the two step sol-gel method. The reaction conditions for the oxidative desulfurization (ODS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over HTS-1 are optimized systematically, and the recycling performances of HTS-1 are investigated in detail. After the 15th run, HTS-1 still maintains high DBT conversion (90.6%) and 4,6-DMDBT conversion (86.0%) without deactivation. The samples before and after recycle tests are characterized by XRD, FT-IR, CHN analysis, UV-Vis and SEM techniques. The results indicate that the crystal structure and morphology of regenerated HTS-1 samples are well kept, which accounts for the good structural stability and reusability of HTS-1. In addition, active intermediates for the ODS of bulky organic sulfides over HTS-1, i.e., Ti-peroxo (Ti-OOtBu) species, are captured by the UV-Vis technique. Finally, a possible reaction mechanism for the ODS process over HTS-1 is proposed.

Well-constructed approach of exceptionally water-stable (mesoporous SiO2)-on-(microporous Cu-BTC) composite for efficient methylene blue capture

A novel (mesoporous SiO2)-on-(microporous Cu-BTC) exhibits good hydrothermal stability and methylene blue capture ability.

Structured cobalt–manganese oxides on SiC nano-whisker modified SiC foams for catalytic combustion of toluene

This work presents a two-step method for preparing structured Cobalt-Manganese Oxides nano-sheet (CMO) on SiC nano-whisker (SNW) modified SiC foam support (i.e. CMO@SNW@SiC) and its application to catalytic combustion of toluene. Firstly, SiC nano-whiskers were synthesized on the surface of SiC foam via carbothermal reduction to increase the specific surface area of the resulting structured support (SNW@SiC). Then, CMO were grown on SNW@SiC by hydrothermal synthesis. SNW@SiC provide more surface area, and the nano-sized SiO2/SiCxOy layer on the surface of the SNW promotes the redox reaction of the reactants on the surface, thereby ensuring the directional growth of CMO on SNW@SiC. Compared to the bare SiC foam, CMO loading was increased 67.5% on SNW@SiC. Analysis methods such as H2-TPR, O2-TPD and XPS prove that the redox ability of the CMO on SNW is similar to that of the powder CMO. Toluene catalytic combustion was used as a probe reaction to evaluate catalytic activity. The results show that the CMO@SNW@SiC catalyst could lower the light-off temperature compared to the CMO supported on SiC foam catalyst, which was equivalent to the bulk catalyst (CMO-24h). At the same time, in comparison with the bulk CMO catalyst, the CMO@SNW@SiC catalyst possessed a higher geometric external surface area, which promoted complete conversion of toluene at lower temperatures. In addition, the stability test shows that the CMO@SNW@SiC catalyst also had very good thermal stability and hydrothermal stability as well. The work provided not only the highly performed catalytic oxidation catalyst, but also presented a generic strategy for improving the design of structured catalysts.

Highly selective zeolite T membranes with different ERI stacking faults for pervaporative dehydration of ethanol

The effect of stacking arrangements of ERI into OFF structure on the separation performance of zeolite T membrane, which was obtained from a modified gel containing a small number of fluoride ions for ethanol dehydration, was investigated for the first time. The addition of fluoride ions and water content largely influenced the zeolite framework structure, the content of ERI stacking, and separation performance.The membrane M3 with MF(NaF: KF = 3:1)/SiO2 and H2O/SiO2 ratio of 0.15 and 35 respectively showed high crystallinity of zeolite T and ordered intergrowth of ERI with the content of about 50–60% estimated by comparing the simulated and observed ratios of (201) and (211) ERI odd lines. The M7 with an H2O/SiO2 ratio of 25 exhibited disordered stacking of ERI in the T membrane. Further increasing MF/SiO2 ratio to 0.20 and 0.25 (M4-M5) or H2O/SiO2 ratio to 45 and 55 (M8-M9) led to the formation of zeolite T membrane with impurity of PHI or CHA structure. The membrane M3 and M7 showed the highest separation index among the reported T membranes for ethanol dehydration with water flux of 2.68 and 1.94 kg·m-2·h-1 and separation factors of 9163 and 10000, respectively. The optimized membrane also exhibited good hydrothermal stability and reproducibility.

Stabilizing the framework of SAPO-34 zeolite toward long-term methanol-to-olefins conversion

As a commercial MTO catalyst, SAPO-34 zeolite exhibits excellent recyclability probably due to its intrinsic good hydrothermal stability. However, the structural dynamic changes of SAPO-34 catalyst induced by hydrocarbon pool (HP) species and the water formed during the MTO conversion as well as its long-term stability after continuous regenerations are rarely investigated and poorly understood. Herein, the dynamic changes of SAPO-34 framework during the MTO conversion were identified by 1D 27Al, 31P MAS NMR, and 2D 31P-27Al HETCOR NMR spectroscopy. The breakage of T-O-T bonds in SAPO-34 catalyst during long-term continuous regenerations in the MTO conversion could be efficiently suppressed by pre-coking. The combination of catalyst pre-coking and water co-feeding is established to be an efficient strategy to promote the catalytic efficiency and long-term stability of SAPO-34 catalysts in the commercial MTO processes, also sheds light on the development of other high stable zeolite catalyst in the commercial catalysis.

Insights into novel mesoporous Cu-SAPO-34 with enhanced deNOx performance for diesel emission control

The formation of ammonium sulfates and existence of mass transportation limits during selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) are severely affecting the de NO x performance of small pore zeolites. Herein, a novel hierarchical porous Cu-SAPO-34-Meso zeolite rich with mesopores was synthesized by one pot dual-template strategy. Cu-SAPO-34-Meso exhibited remarkable de NO x performance and broaden temperature window compared with Cu-SAPO-34-Con without mesopores, especially at low reaction temperature, which should be attributed to the mesopores in Cu-SAPO-34-Meso can accelerate the transportation of the reactants and this has been confirmed by the diffusion calculation. Even exposed on SO 2 feed gas, Cu-SAPO-34-Meso also displayed better SO 2 resistance compared with Cu-SAPO-34-Con. The in situ DRIFTS revealed that the enhanced SO 2 tolerance might be attributed to Cu-SAPO-34-Meso with mesopores could prevent the sulfur species blocking the pores and promote the decomposition of the sulfur species quickly. Therefore, the novel Cu-SAPO-34-Meso catalyst might be a good candidate for real diesel emission control application. • Mesoporous Cu-SAPO-34 with high crystallinity was synthesized. • Cu-SAPO-34-Meso exhibited enhanced NO x removal performance. • Cu-SAPO-34-Meso rich with mesopores can facilitate the mass transportation of the reactants. • Cu-SAPO-34-Meso rich with mesopores displays enhanced SO 2 resistance. • Cu-SAPO-34-Meso exhibit good high and low temperature hydrothermal stability.

An investigation on catalytic performance and reaction mechanism of RuMn/meso-TiO2 derived from RuMn intermetallic compounds for methyl ethyl ketone oxidation

In this work, we first used the oil-phase co-reduction strategy to synthesize the RuxMny (Mn/Ru molar ratio (y/x) = 7 : 20, 21 : 25, and 17 : 10) intermetallic compounds, then used the KIT-6-templeting method to prepare mesoporous titania (meso-TiO2), and finally used the impregnation method to generate the RuxMny/meso-TiO2 (Ru loading = 0.60–0.79 wt%) catalysts. Various techniques were used to measure physicochemical properties of the samples, and their catalytic performance was determined for methyl ethyl ketone (MEK) oxidation. It is found that the RuxMny/meso-TiO2 samples possessed a three-dimensionally ordered mesoporous structure, a surface area of 71–173 m2/g, and a uniform RuxMny particle size of 2.3–2.9 nm. Among all of the samples, Ru25Mn21/meso-TiO2 exhibited the best catalytic performance and good hydrothermal stability: the temperatures at MEK conversions of 10, 50, and 90 % were 131, 226, and 248 °C at a space velocity of 20,000 mL/(g h), with the apparent activation energy, specific reaction rate at 160 °C, and turnover frequency (TOF) at 160 °C being 73 kJ/mol, 41.73 mmol/(gRu s), and 4.20 s−1, respectively. In addition, introduction of 5 vol% moisture to the reaction system exerted a positive effect on catalytic activity of Ru/meso-TiO2 or Ru25Mn21/meso-TiO2 at higher temperatures. Such good performance of the Ru25Mn21/meso-TiO2 sample was related to its well dispersed Ru25Mn21 nanoparticles, high adsorbed oxygen species concentration, active surface lattice oxygen, high MEK adsorption capacity, good redox ability, and strong interaction between Ru25Mn21 and meso-TiO2. We propose that MEK might be oxidized by the adsorbed oxygen and/or surface lattice oxygen species via in turn formation of 2,3-butanedione, acetaldehyde, acetic acid, formaldehyde, and formic acid, all of which were finally converted to water and carbon dioxide.

Recent Progress in a Membrane-Based Technique for Propylene/Propane Separation.

The similar physico-chemical properties of propylene and propane molecules have made the separation process of propylene/propane challenging. Membrane separation techniques show substantial prospects in propylene/propane separation due to their low energy consumption and investment costs, and they have been proposed to replace or to be combined with the conventional cryogenic distillation process. Over the past decade, organosilica membranes have attracted considerable attention due to their significant features, such as their good molecular sieving properties and high hydrothermal stability. In the present review, holistic insight is provided to summarize the recent progress in propylene/propane separation using polymeric, inorganic, and hybrid membranes, and a particular inspection of organosilica membranes is conducted. The importance of the pore subnano-environment of organosilica membranes is highlighted, and future directions and perspectives for propylene/propane separation are also provided.

Ammonia removal in selective catalytic oxidation: Influence of catalyst structure on the nitrogen selectivity

Selective catalytic oxidation is regarded as an effective and favored method for the removal of hazardous ammonia. A number of M-Pt/USY (M=Mn, Fe, Ce and Pr) catalysts were prepared and the resulting materials were characterized using N2 adsorption/desorption, XRD, TEM, NH3-TPD, XPS and H2-TPR. It was found that the addition of non-stoichiometric metal oxides to Pt/USY leads to the generation of additional acid sites for ammonia chemisorption and that N2 selectivity improved with increased strong acidity of the bi-functional catalysts. The oxidation state of active Pt could be adjusted by the introduction of non-stoichiometric metal oxides with increased concentrations of oxidized Ptδ+ species observed in the order of FeOx >CeO2-x >MnO2-x >Pr6O11. High valence platinum surrounded by atomic oxygen that can act as a proton scavenger to drive ammonia activation, inhibiting O2 dissociation and therefore improve N2 selectivity. Fe-containing USY zeolite is demonstrated to be a preferred catalyst for the removal of ammonia, due to its high N2 selectivity and good hydrothermal stability.

Design of amine-functionalized layered double oxide nanosheets with efficient CO2 capture capacities from ambient air, ultrafast kinetics, and promising stability

Recently, the Innovation Team of Energy-Water-Air (ITEWA) from Shanghai Jiao Tong University has carried out researches on direct air capture of CO2. A new family of amine functionalized DAC adsorbent was reported by impregnating branched polyethyleneimine onto mixed metal oxide nanosheets, which exhibits excellent CO2 adsorption capacity (2.27 mmol/g) and kinetics (1.1 mmol/g∙h) under 400 ppm CO2 as well as good thermal stability and hydrothermal stability with almost no performance degradation after 20 adsorption cycles (DOI: 10.1039/D0TA05079B). On this basis, a three-step steam-assisted temperature vacuum swing adsorption (S-TVSA) cycle was designed for DAC (DOI: 10.1016/j.rser.2020.110651). Simulation results show that the S-TVSA cycle could capture CO2 at a rate of 4.45 mol/kg·day. By using novel adsorbents with better adsorption capacities and kinetics, the capture rate can be further increased by 280% and the energy consumption reduced to 32.8%.

One-pot synthesis of fluorine functionalized Zr-MOFs and their in situ growth on sponge for oil absorption

The treatment of oil spill and the separation of oil-water mixture have been widely concerned in recent years. In this work, a one-pot synthesis strategy is developed to prepare fluorine functionalized zirconium-based metal organic framework (Zr-MOFs) (denoted as UiO-66-1F) by using 4-fluorobenzoic acid as modulator and modifier and p-phthalic acid (PTA) as ligand. 4-fluorobenzoic acid can participate in the formation of frameworks structure and cause structural defects, causing larger surface area and hierarchically porous structure. The hydrophobicity of UiO-66-1F increases with increasing of the ratio of 4-fluorobenzoic acid to zirconium chloride and when the ratio is 10, the synthesized UiO-66-1F(10) shows high hydrophobicity with a water contact angle (WCA) of 122° while the WCA of original UiO-66 is only 21°. UiO-66-1F(10) also has good chemical stability over a wide pH range (pH 1∼11) and good hydrothermal stability. In addition, a superhydrophobic sponge (UiO-66-1F(10)@PDA@sponge) with a WCA of 150° was prepared via in situ growth of UiO-66-1F(10) on a polydopamine modified sponge (PDA@sponge). The resulting composite shows high absorption capacities for various oils and organic solvents ranging from 50.5 g/g (n-hexane)– 107.8 g/g (dichloromethane) and good recyclability.

A highly active VOx-MnOx/CeO2 for selective catalytic reduction of NO: The balance between redox property and surface acidity

Excellent catalysts with low-temperature activity and relatively wide temperature window for selective catalytic reduction of NO with ammonia (NH3-SCR) are highly demanded in view of the practical treatment of NO. Herein, we have designed a highly active VOx-MnOx/CeO2 material based on the intrinsic requirement of SCR reaction for catalyst, namely redox sites and surface acid sites. The vanadium oxide and manganese oxide are highly dispersed over the ceria mesosphere via simple incipient wetness impregnation. The loading of manganese could introduce acid sites and enhance the redox property remarkably, while the loading of vanadium increases acid sites and weakens redox property. Through tentatively controlling the appropriate loading ratio of the two components, the optimal catalyst achieves a balance between redox property and surface acidity. The work shed light on the development of new SCR catalyst with superior low temperature activity, wide work temperature window and good hydrothermal stability.

One‐pot synthesis of meso‐microporous ZSM‐5 and its excellent performance in VOCs adsorption/desorption

AbstractBACKGROUNDThe meso‐microporous ZSM‐5 is used for treating the complicated industrial organic waste gas, owing to its good hydrophobicity, excellent thermal and hydrothermal stability, and lower mass transfer resistance than conventional ZSM‐5, resulting in its great adsorption property for volatile organic compounds (VOCs). In this paper, different types of meso‐microporous ZSM‐5 (NZ5, MZ5) were prepared using the templates and then characterized by X‐ray diffraction, infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, and so on. The adsorption/desorption performance and diffusion mechanism of VOCs on meso‐microporous ZSM‐5 were further investigated.RESULTSThe meso‐microporous ZSM‐5 (MZ5), prepared with the cationic surfactant, contained not only large and uniform mesopores but also certain amounts micropores. Moreover, it exhibited excellence adsorption performance for organic molecules due to its relatively reasonable porous structure. The rich porous structure might mean that the cationic surfactant had better effects for producing mesopores in zeolite than the organic additives, such as phenyltriethoxy silane. More importantly, it showed the excellent thermal and hydrothermal stability and great desorption property, which was more than 95% within 20 min at 200 °C. Finally, the diffusion mechanism of toluene on the meso‐microporous ZSM‐5 was investigated, which was suitable for Fick's second law under the low adsorption pressure.CONCLUSIONThe meso‐microporous ZSM‐5 (MZ5, NZ5), prepared by hydrothermal synthesis method with the template, exhibited excellent adsorption/desorption performance, thermal and hydrothermal stability and lower mass transfer resistance than the conventional ZSM‐5 (CZ5) for handling the VOCs. © 2020 Society of Chemical Industry

The Structural and Chemical Properties of the Nile Perch Fish Leather

The conversion of skin to leather involves structural, chemical and physical changes to the material. The changes to the material is often after every subsequent process that the skin goes through before getting to the final leather. The leather processing involves three sub stages; pretanning, tanning and post tanning. The aim of the study was to determine the structural and chemical properties of chrome tanned Nile perch fish leather. The structural properties were determined using scanning electron microscope (SEM). The materials were analyzed for both the surface and cross section. The structural properties were carried out on the raw material then the material was subjected to tanning and there after the structural properties were determined in order to note the change that the tanning has on the structural properties of this particular material. Chrome content was analyzed using atomic absorption spectrometer (AAS) and amount was reported in percentage content. The moisture content was quantified and reported in percentage value.
 From the structural analysis it was noted that the raw material is less compacted as compared to the chrome tanned leather. The fibers of the materials runs in one direction. The speed of the drum needs to be regulated to reduce the destruction of the collagen fibers which largely affects the physical properties of the leather. The average values of chemical properties were reported as follows: Chrome content of 2.45 % and Moisture content of 13.33 ± 1.88 % .The chrome content that was offered in the leather was satisfactory to give it a good hydrothermal stability.

Direct Synthesis of Novel Sponge-Like Porous MnOx Catalysts Derived from Mn-MOFs for High-Efficiently Eliminate o-Dichlorobenzene by Catalytic Combustion

A series of novel lamellar sponge-like MnOx porous catalysts derived from Mn-MOFs have been prepared via modulator-assisted synthesis method and their catalytic performance has been evaluated for o-dichlorobenzene (o-DCB) catalytic combustion reaction. The catalysts were characterized by BET, XRD, Raman, SEM, TEM, XPS, H2-TPR, O2-TPD and other techniques to test the physicochemical properties of the catalysts. The results showed that MnOx had different morphology and properties. The active oxygen species and large specific surface area of MnOx played an important role in the catalytic combustion of o-dichlorobenzene. The T90 of the laminar catalyst MnOx-D, MnOx-D/M, MnOx-D/H/M, and MnOx-D/H was 321, 341, 346, and 355 °C, respectively. MnOx-D has good catalytic activity for the catalytic combustion of o-DCB, which confirmed that surface lattice oxygen played a crucial role in o-DCB combustion. Additionally, they had good hydrothermal stability, thermal stability and water resistance.

Low-Temperature Rapid Synthesis and Performance of the MIL-100(Fe) Monolithic Adsorbent for Dehumidification

MIL-100(Fe) has been proven to have good hydrothermal stability and high vapor uptake and is considered as a promising dehumidification material. However, reduction of the production cost and assem...

Investigation on water vapor adsorption performance of LiCl@MIL‐100(Fe) composite adsorbent for adsorption heat pumps

MIL-100(Fe) with good hydrothermal stability and high hydrophilicity is considered to be a potential adsorbent for adsorption heat pumps (AHPs). However, its water vapor adsorption performance at low relative humidity needs to be improved. In this study, composite adsorbent [email protected](Fe) was synthesized by impregnating LiCl aqueous solution in MIL-100(Fe). The effects of the LiCl loading in the composite on the crystal structure, morphology, composition, pore structure as well as the vapor adsorption/desorption performance of the composites were carefully studied. The results showed that on the premise of ensuring no leakage, the LiCl loading in the composite was up to 32.9 wt%. At 20% relative humidity (RH), the saturated adsorption ratio of the composite (0.260 g/g) was higher than that of original MIL-100(Fe) (0.054 g/g). Meanwhile, the water adsorption rate of the new composite adsorbent was faster than pristine MIL-100(Fe). Moreover, after 50 cycles of vapor adsorption/desorption, the composite adsorbent showed a satisfactory stability. All these indicate that the new [email protected](Fe) composite adsorbent will be a prospective candidate for high-efficiency AHPs.