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Catalytic cracking of naphtha is now a process of huge development potential to produce light olefins, which are important basic raw materials used in various industries, but current industrial catalysts like ZSM-5 zeolites suffer from low selectivity and high energy consumption. Here, Ti/Al-containing nanosize MFI-structure zeolites in-situly synthesized through one-pot method were applied to the catalytic cracking using n-hexane as the model reactant. The maximum mass yield of combined light olefins reaches 49.2% with 99% conversion at 600°C and 1 atm. Multiple characterizations are used to identify the Ti-related active species and their effect on the performance. It was found that a higher proportion of LAS caused by Ti was beneficial to the activation of reactant, and the slightly increased amount of BAS leaded to more alkanes converting into light olefins. This understanding may open new opportunities for design and modification of catalytic cracking catalysts.

Manipulation of zeolite composition through judicious choice of an organic structure-directing agent (OSDA) is essential to regulate its physicochemical properties. ZSM-48 is a unidimensional zeoli...

Crystal engineering of hierarchical zeolites is regarded as a promising way to enhance diffusion-dependent catalytic properties of zeolitic materials. Crystallization process control on crystal size and pore-structure is desirable over porogen based protocols and post-synthetic methods for the low cost, high yield and potential scalability. Herein, a tumbling crystallization of hierarchical ZSM-5 zeolite in immiscible water/toluene Pickering emulsion inspired by energy dissipating structure occurring in nature is presented. The structure and acid properties of the obtained hierarchical material have been revealed using a panoply of characterization techniques such as powder X-ray diffraction, N2 physisorption isotherms, SEM, TEM, mercury protrusion measurements, NH3-TPD and pyridine IR spectroscopy, showing that the material contains high crystallinity, and penetrating macropores. Crystallization is found to proceed through a Pickering emulsion structure maintained by emulsifying effect of constant tumbling. Such an emulsion structure has hindered attachment growth of primary nanocrystals formed at the nucleation stage to further grow into larger size via coalescense. The hierarchical zeolite exhibits architecture-dependent prolonged catalyst lifetime and light olefin yield in dimethylether-to-olefin conversion. This process control to generate hierarchical zeolites opens up new ways toward inexpensive, high level control and efficient engineering of zeolite morphology.

High pressure reforming of methane is critical for process economics, but imposes increased risk of catalyst coke deposition. Herein, a coke- and sintering-resistant Ir-Ni alloy catalyst is presented, which is durable in methane bi-reforming at 850 °C and 20 bars for up to 434 h.

Generation of surface active sites with tailor-made structure is a promising way to enhance catalytic properties of inexpensive metal oxides, as a replacement to noble metals. In the abatement of N...

Generation of hierarchical zeolites is an effective way to enhance their diffusion-dependent catalytic properties. The fabrication of hierarchical zeolites with enhanced diffusion property, high hydrothermal stability, strong acidity in an inexpensive, facile and efficient way is particularly daunting. Here, a simple synthesis of hierarchical SSZ-13 zeolite in a biphasic water/toluene media under tumbling assisted by organosilane, i.e., trimethoxy[3-(phenylamino)propyl]silane, is proposed. The obtained material with tunable Si/Al from 10 to 30 consists of assembled crystallites of 20–30 nm that construct a hierarchical architecture with mesopores of ca. 7 nm opening to the external facets, and has low defect concentration and preserved strong acidity. Crystallization mechanism is disclosed to obey a non-classic attachment growth of nano building blocks mediated by Pickering emulsion, as organosilane modification changes their surface to be hydrophobic. Such a crystallization pathway has accelerated nucleation process and suppressed the growth of SSZ-13 crystals to micron size. Cu exchanged hierarchical SSZ-13 outperforms the standard sample in typical NH3-SCR process in both low and high temperature regimes as a result of enhanced diffusion property, as well as low defect concentrations. The synthesis is a cost-effective method for the generation of hierarchical zeolites mediated by the presence of a liquid/liquid interface, and could inspire more such explorations.

Unidimensional zeolites often form rod-shaped crystals that suffer from low catalytic selectivity or catalyst lifetime owing to their poor diffusion properties. Combined postsynthetic ball-milling and recrystallization methods were investigated to produce unidimensional ZSM-23 crystals with reduced aspect ratio. The influences of ball-milling in the presence/absence of structure directing agent (SDA) and diverse recrystallization media, including H2O, Na2Si3O7 solution, synthetic mixture and mother liquor, over crystallinity, crystal size, textural properties as well as acidity, were intensively explored using characterization techniques such as XRD, SEM, N2 physisorption, 27Al MAS NMR, NH3-TPD, pyridine IR spectroscopy and diffusion measurement. The results showed that crystal size of ZSM-23 was considerably reduced after ball-milling treatment, however, at the expense of crystallinity, acidity and porosity. Recrystallization in the presence of mother liquor was identified as the most effective and economic way to restore crystallinity. The optimized ZSM-23-M-m sample derived from ball-milling in the presence of SDA and a subsequent recrystallization in separated synthesis mother liquor exhibited higher isomer yield (ca. 53%) than the parent sample (ca. 34%) in n-heptane hydroisomerization reaction owing to the enhanced diffusion property and regained acidity after recrystallization.

We present a phase-transfer crystallization approach to the synthesis of ultrasmall (

A continuous flow system that can make the process variable more stable was proposed to prepare NaA zeolite membranes on the inner-surface of alumina hollow fiber, in which the gel solution was recirculated and only preheated at the required section, thus avoiding the unnecessary depletion of the nutrients in the bulk. The influence of synthesis parameters including temperature, flow rate and time over the property of obtained membrane were investigated. The thickness and the morphology of the membranes were explored by SEM. Their separation performance for dehydration of ethanol/water mixture was tested in a pervaporation (PV) set-up with the feed flowing through the membranes’ lumen-side, which varied significantly when the feed flowed at different rates. The reason was inquired by studying the PV behavior at different operating conditions. It was found that the boundary layer resisted the heat transfer, leading to the lower temperature of PV at membrane surface than that of the feed, therefore, the intrinsic PV performance of the membrane could hardly be obtained when the feed flew at low rate. The optimal performance of 19.7 kg/m2 h for the permeation flux and more than 80,000 for the separation factor was tested at the flow rate of 148 mL/min with 90 wt% ethanol/water solution at 348 K, yielding an unprecedented PV performance to our knowledge. The results revealed the high reproducibility and uniformity of the membranes prepared by continuous flow system, as well as that the zeolite membranes located on ceramic hollow fiber inner-surface possessed a competitive advantage of PV performance especially of the permeation flux, which have not been realized by the previous studies and may generalize to the other zeolite or metal-organic frameworks (MOF) membranes.

Controlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties. Herein, we report a single step, Na+ - and porogen- free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b-axis thickness (5-23 nm) and adjustable Si/Al ratios between 35 to 120, employing the commonly used tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) as structure-directing agents (SDAs). Homogeneous nucleation driven by both SDAs and subsequent SDA-exchange induced dissolution-recrystallization are responsible for the formation of such structure. The enhanced textural and diffusion properties account for a notable exaggeration of propene selectivity and catalyst lifetime in dimethyl ether-to-olefins (DTO) conversion. This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control.

The catalytic performance of silicoaluminophosphates is dependent on their acidity and diffusion properties, which can be altered by an organic structure-directing agent (OSDA) as a result of its dominant effect on crystallization. Generally, the solubility of an amine in aqueous media is an important factor for judging whether it is suitable to serve as an OSDA in hydrothermal synthesis of zeolites. This work demonstrates that a hydrophobic molecule, tri-n-heptylamine, could be used as an OSDA for synthesis of hierarchically porous SAPO-31 in biphasic toluene/water media. It provides not only a new method for synthesis of zeolites but also a simple, inexpensive, and porogen-free pathway to generate hierarchical SAPOs. The synthesis allows manipulation of the nSi/(nAl + nP + nSi) ratio from 0.02 to 0.13 without noticeable change of morphological features. The self-assembled, nanocrystalline structure was revealed by combined XRD, SEM/TEM, N2 physisorption, and 27Al, 31P and 29Si MAS NMR spectroscopy, and the acidity was measured with NH3-IR. Catalytic evaluation in n-dodecane hydroisomerization shows that the isomer yield depends on the acid site density of the catalysts, and weak acid strength and high acid site density should be avoided to achieve high selectivity. On the optimized catalyst, the isomer yield has been significantly improved up to 79.7% in contrast to 58.1% for the sample derived from usual hydrothermal synthesis with di-n-hexylamine as an OSDA.

High pressure reforming of methane is critical for process economics, but imposes increased risk of catalyst coke deposition. Herein, a coke- and sintering-resistant Ir-Ni alloy catalyst is presented, which is durable in methane bi-reforming at 850 °C and 20 bars for up to 434 h.

The SUZ-4 zeolite membrane was prepared on the hollow fiber ceramic membrane via the secondary growth method modified by the dynamic hydrothermal process. The surface morphology and pervaporation (PV) performance of zeolite membranes fabricated by dynamic and static hydrothermal processes were studied. The surface of the zeolite membrane prepared by the dynamic hydrothermal process was covered with rod-shaped crystals, while the static one was full of crystal clusters fabricated by small-sized crystals. Besides, the separation factor of the SUZ-4 zeolite membrane made via dynamic hydrothermal method for separating 10 wt% methanol (MeOH)/methyl methacrylate (MMA) mixture at 50 °C exceed 10000 with a flux of 3.83 kg·m−2·h−1, which was better than the static one and showed excellent long-term stability. This work provided the important assistance for the preparation of SUZ-4 zeolite membranes in the separation of MeOH/MMA and MeOH/dimethyl carbonate (DMC) organic mixtures and demonstrated the great potential of dynamic process in promoting the membrane properties.

This paper investigates the influence of reactor structure and operating conditions on dry reforming of methane (DRM), using a two-dimensional reactor model. Two tubular reactors commonly used in the industry are included: one is a mono-tube reactor, the other contains a concentric heating tube. The reactor structure and operating conditions significantly affect temperature distribution and methane conversion in the two reactors. Catalyst dilution in catalyst beds is efficient to control temperature but also largely decreases methane conversion, indicating a balanced packing density of catalyst is required. Reducing the tube radius is useful to control temperature and can save a lot of (in some cases >90%) catalyst, which demonstrates the great potential of using tubular reactors with a small radius. The inlet temperature only slightly changes temperature distribution and methane conversion. The elevated total pressure reduces temperature gradient and also methane conversion, while the feed CH4/CO2 ratio only importantly affects the equilibrium conversion of methane. Comparing temperature distributions and methane conversions in the two reactors, the tubular reactor with a concentric heating tube performs better and uses 11–67% less catalyst. These results should serve to guide the design of tubular reactors for DRM and other highly endothermic reactions.

A single precursor RuxNiyMg1-x-y(OH)(OCH3) derived from solvothermal synthesis was used to generate Ru-Ni-MgO catalysts for methane reforming with CO2. Calcination-reduction pretreatment of precursors could easily cause segregation of Ru and formation of both large and small metallic particles as RuO2 has limited solubility in NiO-MgO solid solution. Uniform small Ru-Ni alloy particles could only be produced within their limited alloying composition range through direct reduction pretreatment of the precursor. Catalysts derived from calcination-reduction exhibited low initial activity that increased with time-on-stream, whereas catalysts derived from direct reduction demonstrated high and steady activity. Over spent catalysts, Ru was found to have changed the type of deposited carbon from a recalcitrant graphitic one that could only be gasified by O2 to a soft type that can be facilely gasified by CO2. Kinetic studies showed that Ru increased the activation barrier for the rate determining CH4 dissociation step and thereby slows down the carbon deposition rate. A first order reaction dependence for CH4 pressure variation and zeroth for CO2 pressure change for pristine Ni- and Ru-catalysts was identified, while a first order and a deviation from zeroth order for CH4 and CO2 pressure variation were observed on bimetallic Ru-Ni catalyst. Such a deviation is associated with the oxyphilic nature of Ru that is enriched in the alloy surface under reforming conditions. The effects of Ru on carbon gasification over spent catalysts were investigated using a modified CO2-TPO measurement based on an extrapolated Wigner–Polanyi equation for carbon gasification. Ru was found to accelerate carbon gasification by increasing the pre-exponential factor for CO2 oxidation of carbon, albeit a disfavored elevated activation barrier was obtained, thus showing a strong compensation effect. Carbon gasification is favored in high concentration of CO2 and at high temperatures for Ru-Ni catalyst.

Changing size and shape of zeolitic crystals brings about enhanced diffusion properties and related promotion of catalytic performances. This work puts forward a phase-transfer synthetic strategy to generate ATO nanocrystalline silicoaluminophosphates spheroids under tumbling crystallization using aluminum isopropoxide dissolved in toluene and other ingredients (fumed silica/phosphoric acid/Di-n-hexylamine) dissolved in water as precursors. Toluene and aqueous phase formed a Pickering emulsion like structure during hydrothermal crystallization. Highly uniform crystalline spheroids of weighted 55 nm with strong acidity and high surface area were obtained, which exhibited a high isomer yield up to 79% in n-heptane hydroisomerization. Comparisons of product distribution and kinetic studies suggest that monomethylbranched isomer selectivity is controlled by product shape selectivity, whereas dimethylbranched isomer selectivity is affected by combined transition state and product shape selectivity. The increase in selectivity for ATO spheroids is attributed to an expansion of intrinsic reaction controlled temperature regime and an improved diffusion property.

Nanosized SAPO-34 has been successfully synthesized by a facile and low-cost method involving an azeotrope evaporation and steam-assisted crystallization route without either expensive poregens or homemade starting materials. The as-synthesized nanosized SAPO-34 shows ultrasmall grain sizes and an impressively high total pore volume, as confirmed by X-ray diffraction, nitrogen physisorption, scanning electron microscopy, and transmission electron microscopy techniques. The formation process and the pivotal role of supersaturation in the synthesis of nanosized SAPO-34 have been revealed by a series of control experiments, on the basis of which a nonclassic oriented attachment mechanism under high supersaturation ratio conditions is proposed. When used as the catalyst for the conversion of chloromethane to olefins, the nanosized SAPO-34 exhibits acidity comparable to that of the conventional SAPO-34 but double the catalytic lifetime and a slightly lower selectivity for light olefins.

The nature of external surface barriers in the zeolite ZSM-5 was explored by comparing mass transfer of n-heptane in samples with different crystal sizes, surface structure, and composition. These different surface properties were achieved by HF acid etching and SiO2 deposition on an as-synthesized ZSM-5 crystal sample. HF etching does not reduce surface barriers. SiO2 deposition on the same sample reduces surface barriers significantly. These insights into the nature of surface barriers could be used to guide the rational design of zeolitic materials with better mass transport properties.

Cobalt-based layered metal compound (Co(OH)(OCH 3 )) nanoplatelets synthesized by a facile solvothermal method were systemically characterized and investigated as an anode material for Li-ion batteries for the first time. It can deliver a high capacity of 1150 mA h g −1 at 100 mA g −1 and stay stable even after 160 cycles. It also shows high rate performance and reversibility. Its good electrochemical performance might be attributed to the unique layered structure with large layer spacing, 2D nanoplatelet-like morphology, and the void space between the nanoplatelets. The present synthesis strategy develops a potential candidate for anode materials with good performance for lithium-ion batteries.

Currently, the application of supercapacitors (SCs) in portable electronic devices and vehicles is limited by their low energy density. Developing high-energy density SCs without sacrificing their advantages, such as their long-term stability and high power density, has thus become an increasing demand but a major challenge. This demand has motivated tremendous efforts, especially towards discovering and optimizing the architecture of novel electrode materials. To this end, we herein report the design, synthesis, and SC application of a new family of two-dimensional (2D) nanoplatelets, i.e., a transition-metal hydroxymethylate complex (Ni x Co1–x (OH)(OCH3)). Bimetallic nanoplatelets were synthesized via a cost-effective approach involving a one-step solvothermal procedure. We for the first time tuned the metal composition of these 2D nanoplatelets over the entire molar-fraction range (0–1.0). Tuning the molar ratio of Ni/Co allowed us to optimize the structures and physicochemical properties of the nanoplatelets for SC applications. When tested in a half cell, SC electrodes using the nanoplatelets exhibited high electrochemical performance with a specific capacitance as high as 1,415 F·g–1 and a 96.1% retention of the initial capacitance over 5,000 cycles. We exploited the novel 2D nanoplatelets as cathode materials to assemble a hybrid SC for full-cell tests. The resulting SCs operated in a wide potential window of 0–1.7 V, exhibited a high energy density over 50 Wh·kg–1, and sustained their performance over 10,000 charge–discharge cycles. The results suggest that the novel 2D nanoplatelets are promising alternative materials for the development of high-energy density SCs.

Transforming natural kaolin into pure-phase hierarchical aggregates of nano ZSM-11 has been achieved by using a novel tetrabutylphosphonium hydroxide as a structure-directing agent via steam-assisted crystallization. The hierarchical ZSM-11 possesses a small particle size (about 240 nm), large surface area (428 m2 g−1), and abundant mesopores (0.30 cm3 g−1). Moreover, the hierarchical ZSM-11 exhibits prolonged catalytic lifetime and promoted aromatic selectivity in the methanol-to-aromatics reaction. The superior catalyst stability is attributed to the better capacity of accommodating the coke and a lowered coking rate.

Phenyltrimethoxysilane as a Si source can significantly slow down the crystallization process for SAPO-34 synthesis, leading to the formation of agglomerated nanocrystals (

1,3-Propanediol, a vital monomer for the manufacture of commodity polytrimethylene-terephthalate, is commercially produced nowadays through either hydration of acrolein or hydroformylation of ethylene oxide. Herein, for the first time, we present the investigation of an alternative route for 1,3-propanediol production from vapor-phase catalytic hydrogenation of syngas-derived dimethyl malonate on a Cu/SiO2 catalyst. The catalytic reaction network has been disclosed for the Cu/SiO2 catalyst, and the reaction proceeds through sequential hydrogenation with methyl 3-hydroxypropionate as the primary product, which can be further converted into 1,3-propanediol or methyl propionate. Excessive hydrogenation of 1,3-propanediol or methyl propionate leads to the formation of n-propanol. Meanwhile, a small amount of dimethyl malonate cracks into methyl acetate. The structural and textural properties of Cu/SiO2 catalysts with varied copper loadings were extensively characterized by X-ray diffraction, Fourier transform infrared spectroscopy, H2-temperature programmed reduction, X-ray photoelectron spectroscopy, N2 physisorption, CO chemisorption, N2O titration, and transmission electron microscopy. A correlation of the areal activity to copper components suggests that metallic copper modified by the co-present Cu+ species may be the active site for the hydrogenation. The highest 1,3-propanediol selectivity was achieved on a catalyst with a maximum Cu+/(Cu0 + Cu+) ratio of 0.41. The revelation of catalytic networks and insights into the active species can provide guidance for future rational design of catalysts for regioselective hydrogenation of CO bonds in dimethyl malonate.

Surface modification is an efficient post-treatment method to optimize the properties of nanofiltration (NF) membranes. Here, we report a facile surface modification strategy coupling with heat curing for grafting monoethanolamine (MEA), a monomer containing both a primary amine and a primary alcohol group, onto a nascent polyamide NF membrane. With grafting 0.5 wt% MEA at 50 °C, the pure water permeability of the polyamide NF membranes was improved from 7.9 to 19.5 L m−2 h−1 bar−1 due to their enhanced physicochemical property, such as superior hydrophilicity, rough surface morphology, and enlarged membrane pores. Meanwhile, the rejection of Na2SO4 remained above 97.5%. More importantly, the optimal membrane modified with 0.5 wt% MEA exhibited a high Na2SO4 rejection of 99.1% and a negative NaCl rejection of −20.1% when treating a mixed salt solution containing 2 g/L Na2SO4 and 2 g/L NaCl. Our study provides a novel insight for the fabrication of high permselectivity NF membranes via surface modification.

Understanding silicoaluminophosphate formation mechanism lays the foundation for their structure manipulation via crystallization process control. Crystallization of SAPO-34 from a dry gel using tetraethyl ammonium hydroxide as structure-directing agent was monitored to unravel the formation mechanism. The initial gel was found to form a lamellar precursor first, which subsequently underwent phase transformation to discrete SAPO-34 nanocrystallites. The nanocrystallites thereafter mutually aligned with neighboring ones via a non-classic oriented attachment growth mechanism, affording large crystals as a result of grain boundary elimination. A new protocol to prepare hierarchical SAPO-34 was designed by hindering the aggregation of primary nanocrystallites with a growth inhibitor 1,2,3-hexanetriol. The structure of hierarchical SAPO-34 was characterized by XRD, N 2 physisorption, mercury intrusion, SEM, TEM, as well as 27 Al, 29 Si, 31 P MAS NMR spectra and compared with a conventional SAPO-34. More Si islands were formed via combined SM3 (Al+P pairs substitution by 2Si) and SM2 (P substitution by Si) mechanism for hierarchical SAPO-34 as Si was not fully incorporated into the precursor lamellar phase. NH 3 -TPD showed that hierarchical SAPO-34 has comparable acidic strength to conventional SAPO-34. The obtained hierarchical SAPO-34 is comprised of

Methane is an important product in methanol to hydrocarbon (MTH) process and its formation mechanism over HZSM-5 was investigated by applying periodic density functional theory. The results show that the carbocations of C 7 H 9 + –C 12 H 19 + are important intermediates in MTH process and methane is formed via one intramolecular hydrogen transfer reaction of these intermediates from ring carbon to the carbon of methyl group. The activation energies for methane formation increase from 101 to 174 kJ/mol with increasing methyl groups in protonated methylbenzenes. The data indicate that methane has similar formation mechanism as ethene and propene, i.e. via hydrocarbon pool mechanism.

Integrating hierarchical porosity over microporous zeotype materials is an effective way to promote their mass transfer properties and catalytic performances. A combined synthetic strategy using small molecular growth inhibitor 1,2,3-hexanetriol and tumbling crystallization condition to generate hierarchically organized SAPO-11 is herein presented. The addition of 1,2,3-hexanetriol in the synthetic gel of SAPO-11 under agitating conditions significantly altered its crystallization behaviour, resulting in the formation of a hierarchically organized architecture. An underlying nonclassical from-shell-to-core crystallization has been disclosed by time-dependent observation of the formation process. The hierarchically self-organized structure has been characterized by a suite of characterization techniques, such as XRD, N2 physisorption, SEM, TEM, mercury intrusion measurements, 27Al, 29Si, 31P MAS NMR and pyridine adsorption IR (Py-IR). The structure featuring barrel-shaped architecture is comprised of aligned 300–400 nm primary building blocks with voids in between, constructing an auxiliary macro-/meso-pore system open to external surfaces. The catalytic performance of Pt supported on hierarchical SAPO-11 in n-heptane hydroisomerization has been assessed, showing that both catalytic activity and isomer yield have been increased with respect to a conventional sample. As the acidity for the hierarchical SAPO-11 is comparable to the conventional sample, the enhancement in catalytic performance is attributed to the small primary crystal size and macro-/meso-pore-connectivity, that are important for mass transfer.

Silicoaluminophosphates SAPO-41 is a superior unidimensional zeotype catalyst used in hydroisomerization. Generation of hierarchically structured SAPO-41 provides an effective way to promote its hydroisomerization selectivity, which is nonetheless difficult to achieve due to the formation of impurities. Herein, we report crystallization of plate-like crystals of pure phase SAPO-41 in a toluene-aqueous biphasic media in the presence of both Pr2NH and oleylamine. The obtained material has a larger adjustable range of silicon content (nSi/(nAl+nSi+nP) = 0.02−0.15), intermediate acidity and reduced diffusion path length along the micropore channel direction. Catalytic tests for n-heptane hydroisomerization on Pt loaded plate-like SAPO-41 crystals showed that the yield of the isomerized products could reach up to 68 %, with respect to 57 % for a control sample. The selectivities for isomers were found to increase with decreasing Si contents and enhanced diffusion properties, suggesting side β-scission reaction was disfavored at reduced acid site density and shortened diffusion path length.

Nanofiltration (NF) membranes with both high permeability and salt rejection are in dire need for water treatment. Generally, heat treatment is an essential step for fabricating polyamide NF membranes. Conventional heat treatment in an oven causes membrane pore shrinkage and over cross-linking, which often leads to a severe loss of permeation performance. Herein, we report a single-step method by heat-treating membranes in non-neutral solutions to avoid pore shrinkage and generate graded hydrolysis in membrane selective layer. As confirmed by the XPS result, the polyamide NF membrane fabricated via controlled hydrolysis possesses a gradient cross-linking degree vertically along the membrane surface. This optimal polyamide NF membrane had a superior pure water permeability (PWP) of 27.5 L m−2 h−1 bar−1 and high Na2SO4 rejection of 98.5%. Such controlled hydrolysis approach provides novel strategy for fabricating high performance polyamide membranes.

Dry reforming of methane (DRM) converts two major greenhouse gases into syngas, a versatile chemical feedstock, requiring the identification of a robust catalyst. In this contribution, we explored the promoting effect of Fe in MgO supported Ni-Fe alloy catalysts in DRM. Towards this end, a series of catalysts with varied Fe/(Ni+Fe) ratios (0 to 0.17) and homogeneous metal distribution were prepared from a single FexNiyMg1-x-y(OH)2 (x = 0.00–0.07, y = 0.00–0.07) precursor derived from solvothermal synthesis. Catalytic evaluations at 760 °C and 800 °C showed that Fe passivated the activity of Ni surface while promoting the coke-tolerant property. Structural evolution and coke deposition of catalysts were extensively characterized by using XRD, SEM, TEM, HAADF-HRTEM, H2-TPR, CO2 (O2)-TGA and CO2-TPO techniques, manifesting that alloying of Fe with Ni had enhanced catalyst stability. Lowered amount of coke was found on spent Ni-Fe alloy catalysts with respect to pristine Ni catalyst, and Fe also changed the type of surface carbon from a refractory type to a soft one that can be readily gasified by CO2. Fe also increased the surface oxyphilicity of alloy particle surface via balancing the otherwise carbon affinity of Ni surface. Optimized catalytic performance was attained by FexNi0.07-xMg0.93O-R (x = 0.003–0.006) catalyst. Kinetic studies and coke gasification kinetic disclosed that Fe slowed down coke deposition rate and concomitantly accelerated surface coke gasification rate, without changing the essential reaction mechanism or kinetic features of pristine Ni catalyst. The promoting effect of Fe was found to be highly dependent on CO2 contents in the contacting atmosphere, as well as Fe/Ni ratios in the alloy. The stability of Ni-Fe alloy catalyst in DRM can be ascribed to combined effects from both ensemble size reduction and surface oxyphilicity change. The role Fe plays in enhancing DRM coke-resistant property is potentially useful for alike reforming catalyst and process design.

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na2SO4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane.

The effects of alkaline treatment on the physical properties of ZSM-5 catalysts and on their activities for methanol to aromatics conversion have been investigated. A mild alkaline treatment (0.2 and 0.3 mol/L NaOH) created mesopores in the parent zeolite with no obvious effect on acidity. The presence of mesopores gives the catalyst a longer lifetime and higher selectivity for aromatics. Treatment with 0.4 mol/L NaOH decreased the number of Bronsted acid sites due to dealumination and desilication, which resulted in a lower deactivation rate. In addition, more mesopores were produced than with the mild alkaline treatment. As a result, the lifetime of the sample treated with 0.4 mol/L NaOH was almost five times that of the parent ZSM-5. Treatment with a higher alkaline concentration (0.5 mol/L) greatly reduced the number of Bronsted acid sites and the number of micropores resulting in incomplete methanol conversion. When the alkaline-treated catalysts were washed with acid, some of the porosity was restored and a slight increase in selectivity for aromatics was obtained.

Carbon nanotubes (CNTs) can be well dispersed in an ethanol diluted zeolite precursor and thus encapsulated in the formed dry gel after solvent evaporation. This specially prepared dry gel allows small quantites of CNTs to effectively act as transient inhibitors in the subsequent steam-assisted crystallization of ZSM-5 nanocrystal aggregates with hierarchical porosity. Although finnally separated from zeolite, CNTs can still transiently inhibit the zeolite growth to avoid fusing into a large crystal. The inter-crystalline mesoporosity in hierarchical ZSM-5 is not created by the space occupied by CNTs, but preserved from the mesoporosity formed by nucleation and initial crystallization. Excessive quantities of CNTs are not recommended because their excessive inhibition induces the appearance of amorphous impurity in hierarchical ZSM-5.

Finding controllable, low-cost, and scalable ways to generate Ni-based catalysts is the bottleneck for methane dry reforming catalyst design. A new method for generating trimetallic Co x Ni y Mg 100 − x − y O solid solution platelets enclosed by (1 1 1) facets has been developed from the topotactic pyrolysis of the metastable precursor Co x Ni y Mg 100 − x − y (OH)(OCH 3 ) derived from solvothermal synthesis. The catalyst composition and reaction conditions have been modulated to achieve maximum coke resistance and catalyst stability. Long-term stability for 1000 h time on stream at 800 °C has been achieved for the optimized Co 0.075 Ni 7.425 Mg 92.5 O catalyst. The role of Co in the catalyst has been disclosed through kinetic measurements and detailed characterization of the spent catalysts. Co is enriched on the Co–Ni alloy surface under reforming conditions and accelerates the gasification of coke intermediates. Co also enhances the chemisorption of oxygen and reduces the activation energy for methane fragmentation, which is the rate-determining step for the overall reaction.

This paper shows that a uniform spatial distribution in meso/macroporosity of adsorbents maximizes their adsorption and desorption performance. It highlights the importance of optimizing porosity and pore diameter, not only at the nanoscale but also at larger length scales. The effects of spatial pore size and porosity distributions on mass transfer in adsorbents are studied by using a continuum approach. These effects are evaluated by comparing the adsorption/desorption performance of adsorbents subjected to a square wave concentration perturbation with a wide range of cycle period (10–100,000 s) for the adsorption of n-pentane on 5A zeolite adsorbents. The uniformly distributed pore size and porosity is the preferred structure, which is confirmed by using four empirical tortuosity–porosity relations. Further optimization of the uniform structure shows that its optimal average porosity is in the range of 0.4–0.6 when the perturbation cycle period is between 100 s and 2000 s and the volume-averaged pore diameter is between 10 nm and 150 nm. The relationships between optimal average porosity, cycle period and volume-averaged pore diameter are determined and explained. These results should serve to guide the synthesis of adsorbents.

Zeolites belong to microporous solids that are widely used as adsorbents, catalysts and catalyst supports. As diffusion in the microspores is slow, it is highly desirable to develop approaches to enhance mass transfer or to avoid the negative effect from mass transfer resistance. In this perspective, we underline pore architecture control for hierarchical zeolite, and spatial locations of metal nanoparticles on zeolite. For solid acid catalysts, the construction of auxiliary porosity in crystalline zeolites leading to the formation of hierarchical zeolite is a promising solution. Most successful pore-architecture construction strategies are based on templating approaches within the classic LaMer crystallization framework, whereas our strategies are based on the non-classic orientated attachment growth mechanism in dry gel crystallization. Organic additives, such as organosilanes, can be incorporated with protozeolite particles to produce hybrid mesocrystals. Combustion of organics in the mesocrystal affords hierarchical beta zeolites, the pore-architecture of which is tunable with respect to additive selection. Such a crystallization based design of pore-architecture merits small primary crystal size and improved pore-connectivity, which have been verified to be the key factors that affect diffusion. On the other hand, for zeolite supported metal catalysts that suffer from deactivation caused by pore blocking, we propose a strategy to avoid the deactivation problem by depositing metal nanoparticles exclusively on the external surfaces of support. This can be achieved by simply leaving the structure directing agents in the pores before supporting metal particles. Side reactions caused by diffusion resistance are minimized, and moreover, the involatile byproducts, if any, do not produce additional diffusion resistance. Such a simple yet effective architecture control significantly prolongs the lifetime of Au/TS-1 catalyst in direct propene epoxidation with H2 and O2. From these demonstrations, it is important to design purpose-orientated zeolite synthesis to enhance mass transfer, for which the architecture plays a key role.

The catalytic performance of Ag promoted Ni/CeO2 catalyst has been investigated in methane and carbon dioxide dry reforming reaction. The temperature-dependent catalytic activity and time-on-stream catalytic performance at 760 °C under different feeding conditions have been explored. Pristine Ni/CeO2 is not stable as a result of coke deposition and surface reconstruction. In addition, co-feeding of H2 can adversely influence the long-term stability of Ni/CeO2. Ag severely reduces the intrinsic catalytic activity of Ni/CeO2 catalyst, while enhances the long-term stability by diminishing coke deposition. Ag is applicable as a promoter under various reaction conditions, from N2 diluted feedstock to H2 co-fed and carrier-gas free feedstock. Kinetic studies show that Ag elevates the activation energy from 91 to ca. 140 kJ/mol by a loading of 0.3 mol.%, excessive Ag loading does not affect activation energy. The role of Ag is to block step sites on Ni surface that is associated with carbon nucleation and growth, and to promote gasification of coke formed. Besides, Ag alters the type of coke formed over Ni surface from recalcitrant whisker/encapsulating carbon to easily gasifiable amorphous carbonaceous species.

Oxygen evolution from water poses a significant challenge in solar fuel production because it requires an efficient catalyst to bridge the one-electron photon capture process with the four-electron oxygen evolution reaction (OER). Here, a new strategy was developed to synthesize nonsupported ultrasmall cobalt oxide nanocubanes through an in situ phase transformation mechanism using a layered Co(OH)(OCH3) precursor. Under sonication, the precursor was exfoliated and transformed into cobalt oxide nanocubanes in the presence of NaHCO3-Na2SiF6 buffer solution. The resulting cobalt catalyst with an average particle size less than 2 nm exhibited a turnover frequency of 0.023 per second per cobalt in photocatalytic water oxidation. X-ray absorption results suggested a unique nanocubane structure, where 13 cobalt atoms fully coordinated with oxygen in an octahedral arrangement to form 8 Co4O4 cubanes, which may be responsible for the exceptionally high OER activity.

A dry gel derived from a conventional hydrogel (or an ultrasonically treated hydrogel) containing a low amount of tetraethylammonium hydroxide (TEAOH) was subjected to a vapor-phase transport procedure using morpholine and produced SAPO-34 around 300–500 nm (or below 100 nm). The formation of small crystals has mainly benefited from the increase in tetra-coordinated Al atoms in the dry gel promoted by heating and/or ultrasonic treatment.

Glycerol-mediated crystallization transforms a steam-treated dry gel used as the mesoporous precursor into a hierarchical ZSM-5 zeolite. The hierarchical ZSM-5 zeolite with auxiliary mesoporosity and acidity exhibits higher activity in the aldol condensation reaction of benzaldehyde with n-butyl alcohol.