Double Unit-Cell Silicogermanate Nanosheets Developed by Salting-Out Mechanism for Biomass Conversion.

Zeolite nanosheets with an extremely thin thickness featuring both unique pore systems and low diffusion resistance have the potential to achieve enhanced catalytic performance in the conversion of bulky molecular biomass. The preparation of unit-cell level nanosheets generally requires complex and costly multifunctional surfactants or an organic structure-directing agent (OSDA). Commercially available and environmentally friendly ionic liquids can also direct the structure of zeolite nanosheets by π-π stacking when these kinds of OSDA are used in large amount. Herein, we first report unit-cell-sized silicogermanate nanosheets of NS-IM-20 (UWY topology), 5 nm in thickness, which were synthesized at a relatively low ionic liquid concentration with the assistance of halide ion (Cl-). The Pd-loaded NS-IM-20 nanosheets with a hierarchical porosity and moderate acidity act as promising bifunctional catalysts for selective biomass conversion.

Promoting Syngas to Olefins with Isolated Internal Silanols-Enriched Al-IDM-1 Aluminosilicate Nanosheets.

Selective conversion of syngas to value-added olefins has attracted considerable research interest. Regulating product distribution remains challenging, such as achieving higher olefin selectivity, propylene/ethylene (P/E) and olefin/paraffin (O/P) ratios. A new pentasil zeolite Al-IDM-1 with recently approved -ION structure, composed of 17-membered-ring (MR) extra-large lobed pores and intersected 10-MR medium pores, shows a C2-6 = selectivity up to 85 % and a high O/P value of 14 in the conversion of syngas when being combined with Zna Alb Ox oxide. Moreover, for the high-silica Al-IDM-1 with Si/Al ratio of 400, the selectivity of propylene and butene accounts for 88 % in C2-4 = , resulting in high P/E (>4) and butene/ethylene (B/E >3) ratios. The high C3-4 = selectivity is contributed by two main reasons, that is, the relatively weak acidity of Al-IDM-1 zeolite enhances the olefin-based cycle revealed by the probe reactions of methanol-to-propylene (MTP) and 1-hexene cracking, and the rich isolated internal SiOH groups in Al-IDM-1 promote the desorption of C3-4 = , once they are formed inside zeolite pores.

Green carbon science: fundamental aspects.

Carbon energy has contributed to the creation of human civilization, and it can be considered that the configuration of the carbon energy system is one of the important laws that govern the operation of everything in the universe. The core of the carbon energy system is the opposition and unity of two aspects: oxidation and reduction. The operation of oxidation and reduction is based on the ternary elemental system composed of the three elements of carbon, hydrogen and oxygen. Its operation produces numerous reactions and reaction products. Ancient Chinese philosophy helps us to understand in depth the essence of green carbon science, to explore its scientific basis, and to identify the related platforms for technology development.

Directing Highly a-Axis-Oriented ZSM-5 Nanosheets with Pre-estimated Bifunctional Imidazole Cations.

An MFI-topology nanosheet zeolite with a highly a-axis-oriented structure has rarely been reported but with a great potential for industrial applications. Theoretical calculations on the interaction energies between the MFI skeleton and ionic liquid molecules indicated the possibility of preferential crystal growth along a specific direction, according to which highly a-oriented ZSM-5 nanosheets were synthesized from commercially available 1-(2-hydroxyethyl)-3-methylimidazolium and layered silicate sources. The imidazolium molecules directed the structure formation and meanwhile acted as zeolite growth modifiers to restrict the crystal growth perpendicular to the MFI bc plane, which induced unique a-axis-orientated thin sheets with ∼12 nm thickness. The a-oriented ZSM-5 exhibited more competitive propylene selectivity and longer lifetime than bulky crystals in methanol-to-propylene (MTP) reaction. This research would provide a versatile protocol for the rational design and synthesis of shape-selective zeolite catalysts with promising applications.

Layered Zeolite for Assembly of Two-Dimensional Separation Membranes for Hydrogen Purification.

Membrane separation is an energy-efficient and environmentally friendly process. Two-dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High-aspect-ratio zeolite nanosheets with intrinsic molecular-sieving pores perpendicular to the layers are desirable building blocks for fabricating high-performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU-28, with SZR topology and eight-member ring (8-MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture.

ECNU-13: A High-Silica Zeolite with Three-Dimensional and High-Connectivity Multi-Pore Structures for Selective Alkene Cracking.

A high-silica zeolite ECNU-13 (Si/Al=23) with a new three-dimensional (3D) pore system and a nanosized morphology has been developed, consisting of multitudes of 10-membered ring (10-R) medium pores and one set of 8-R small pores. A phase-discrimination strategy was proposed to synthesize ECNU-13 by regulating the gel compositions and nucleation processes that were used for preparing 12-R large-pore germanosilicate IM-20 with the known UWY topology. The crystallization was directed towards forming one set of single four-ring (s4r) composite building units together with one set of double four-ring (d4r) rather than two different types of d4r units in IM-20. The electron crystallographic investigations elucidated that the ECNU-13 structure was composed of two kinds of polymorphs as a result of distinct atomic positionings in s4r units. In catalytic cracking of 1-butene, ECNU-13 exhibited high propene selectivity (55.6 %) and propene to ethylene molar ratio (>4.7) superior to well-studied conventional ZSM-5 zeolite catalyst.

Direct synthesis of IDM-1 aluminosilicate nanosheets with improved MTP performance.

Aluminosilicate nanosheets with pure IDM-1 structure, abbreviated as Al-I1, were rapidly synthesized by adjusting the F sources. Through preliminary aging, the length along the b-axis of Al-I1 was precisely tuned in the range of 40-200 nm and meanwhile the competitive growth to the MFI phase was suppressed. With improved mass transport owing to expanded pores and shortened diffusion path along the b-axis, the Al-I1 nanosheets exhibited superior catalytic performance to conventional b-axis oriented ZSM-5 in the methanol-to-propylene (MTP) reaction. The optimal Al-I1-40 catalyst with the thinnest thickness of 40 nm showed a long catalytic lifetime of 67 h and a high propylene selectivity of up to 57.1%.

Designing SAPO-18 with energetically favorable tetrahedral Si ions for an MTO reaction.

The silicon site location in silicoaluminophosphate zeolites has significant influences on their acidic and catalytic properties. Herein, AEI analogue silicoaluminophosphates with controlled tetrahedral silicon centers (T sites) were synthesized using specially designed amines as expected organic structure-directing agents (OSDAs). DFT calculations show that the OSDAs with different electronegativity can direct Si atoms into the T sites with more favorable energy advantages. Their catalytic performances in a methanol-to-olefin (MTO) reaction also reflected that OSDAs controlled the Si location in the framework, and the T3 sites had better performance than T1 sites. This finding provides evidence that OSDAs are capable of guiding the Si ions into more favorable T sites, achieving desirable catalytic properties as solid acid catalysts.

Total Hydrogenation of Furfural under Mild Conditions over a Durable Ni/TiO2-SiO2 Catalyst with Amorphous TiO2 Species.

One-step total hydrogenation of furfural (FAL) toward tetrahydrofurfuryl alcohol in continuous flow using cheap transition metals still remains a great challenge. We herein reported the total hydrogenation of FAL over Ni (∼5 nm) nanoparticles loaded on TiO2-SiO2 composites with long-term stability. The TiO2-SiO2 composites comprise amorphous TiO x which was grafted on the silica aerogel by acetyl acetone-aided controlled hydrolysis of tetrabutyl titanate. The catalysts were characterized by several techniques including Brunauer-Emmett-Teller, X-ray diffraction, transmission electron microscopy, H2-temperature-programmed reduction, and H2-temperature-programmed desorption. The hydrogenation performances were systematically explored in terms of TiO2 content, Ni loading, liquid hour space velocity, and so forth. Ni nanoparticles in contact with amorphous TiO x showed strengthened interaction with the C=O bond of FAL as well as enhanced hydrogen dissociation and desorption ability, hence benefiting the overall hydrogenation process.

ECNU-36: A Quasi-Pure Polymorph CH Beta Silicate Composed of Hierarchical Nanosheet Crystals for Effective VOCs Adsorption.

A quasi-pure CH polymorph of microporous zeolite beta, named ECNU-36, was obtained as a highly crystalline silicate using 1,5-bis(tetramethylimidazolium) hydroxide as organic structure-directing agent (OSDA) in fluoride media. An appropriate concentration of free fluoride in the synthetic mother liquor was crucial to purify the CH -phase. The framework structure of ECNU-36 consists of polymorph CH (>95 %) and polymorph B, elucidated by a combination of PXRD data, DIFFaX simulation, EDT, and HRTEM techniques. For the first time, the framework structure of beta CH polymorph was directly confirmed and solved using electron diffraction data. The pure-silica ECNU-36 showed an unusual crystal morphology, composed of stacked nanosheets, with typical 17 nm thickness and exposed {100} facets, which exhibited attractive adsorption performance for hydrocarbons and aromatics.

Hydrothermal synthesis of boron-free Zr-MWW and Sn-MWW zeolites as robust Lewis acid catalysts.

An innovative strategy based on dual structure-directing agent-facilitated crystallization was proposed to hydrothermally synthesize boron-free Zr-MWW and Sn-MWW metallosilicates that bear great structural diversity for potential pore engineering. The metallosilicates show distinctive features in Lewis acid-catalyzed reactions as efficient heterogeneous solid catalysts.

The (p)ppGpp-mediated stringent response regulatory system globally inhibits primary metabolism and activates secondary metabolism in Pseudomonas protegens H78.

Pseudomonas protegens H78 produces multiple secondary metabolites, including antibiotics and iron carriers. The guanosine pentaphosphate or tetraphosphate ((p)ppGpp)-mediated stringent response is utilized by bacteria to survive during nutritional starvation and other stresses. RelA/SpoT homologues are responsible for the biosynthesis and degradation of the alarmone (p)ppGpp. Here, we investigated the global effect of relA/spoT dual deletion on the transcriptomic profiles, physiology, and metabolism of P. protegens H78 grown to mid- to late log phase. Transcriptomic profiling revealed that relA/spoT deletion globally upregulated the expression of genes involved in DNA replication, transcription, and translation; amino acid metabolism; carbohydrate and energy metabolism; ion transport and metabolism; and secretion systems. Bacterial growth was partially increased, while the cell survival rate was significantly reduced by relA/spoT deletion in H78. The utilization of some nutritional elements (C, P, S, and N) was downregulated due to relA/spoT deletion. In contrast, relA/spoT mutation globally inhibited the expression of secondary metabolic gene clusters (plt, phl, prn, ofa, fit, pch, pvd, and has). Correspondingly, antibiotic and iron carrier biosynthesis, iron utilization, and antibiotic resistance were significantly downregulated by the relA/spoT mutation. This work highlights that the (p)ppGpp-mediated stringent response regulatory system plays an important role in inhibiting primary metabolism and activating secondary metabolism in P. protegens.

High Ethylene Selectivity in Methanol-to-Olefin (MTO) Reaction over MOR-Zeolite Nanosheets.

Precisely controlled crystal growth endows zeolites with special textural and catalytic properties. A nanosheet mordenite zeolite with a thickness of ca. 11 nm, named as MOR-NS, has been prepared using a well-designed gemini-type amphiphilic surfactant as bifunctional structure-directing agent (SDA). Its benzyl diquarternary ammonium cations structurally directed the formation of MOR topology, whereas the long and hydrophobic hexadecyl tailing group prevented the extensive crystal growth along b axis. This kind of orientated crystallization took place through the inorganic-organic interaction between silica species and SDA molecules present in the whole process. The thin MOR nanosheets, with highly exposed (010) planes and 8-membered ring (MR) windows, exhibited a much improved ethylene selectivity (42.1 %) for methanol-to-olefin (MTO) reactions when compared with conventional bulk MOR crystals (3.3 %).

Improvement of pyoluteorin production in Pseudomonas protegens H78 through engineering its biosynthetic and regulatory pathways.

Pyoluteorin (Plt) is a PKS-NRPS hybrid antibiotic that is produced by Pseudomonas spp. and shows strong antifungal and antibacterial activities. Pseudomonas protegens H78, which was isolated from the rape rhizosphere in Shanghai, can produce a large array of secondary metabolites, including antibiotics and siderophores. Plt is produced at low levels in the H78 wild-type strain. This study aimed to improve Plt production through combinatory genetic engineered strategies. Plt production was significantly enhanced (by14.3-fold) in the strain engineered by the following steps: (1) deletion of the translational repressor gene rsmE in the Gac/Rsm-RsmE pathway; (2) deletion of the ATP-dependent protease gene lon that encodes a potential enzyme that degrades positive regulators; (3) deletion of the negative regulatory gene pltZ of the Plt ABC-type transporter operon pltIJKNOP; (4) deletion of an inhibitory sequence within the operator of the transcriptional activator gene pltR; and (5) overexpression of the pltIJKNOP transport operon. The Plt production of the final engineered strain was increased to 214 from 15 µg ml-1 in the H78 wild-type strain. In addition, the pltA gene in the pltLABCDEFG biosynthetic operon was characterized as the gene encoding the rate-limiting enzyme in the Plt biosynthetic pathway of H78. However, overexpression of the rate-limiting enzyme gene pltA or the transcriptional activator gene pltR did not further improve Plt biosynthesis in the above multiple-gene knockout strains.

Doping Pd/SiO2 with Na+: changing the reductive etherification of C[double bond, length as m-dash]O to furan ring hydrogenation of furfural in ethanol.

The production of biofuels and chemicals by hydrogenation of furfural has attracted much attention recently. Herein the effect of Na+ doping on the catalytic performance of Pd/SiO2 in hydrogenation and reductive-etherification of furfural in ethanol was systematically studied. Two Pd/SiO2 catalysts with and without the modification by Na+ were prepared by impregnation and calcination. Their catalytic properties were compared for the hydrogenation of furfural and furfural diethyl acetal under mild conditions. The silanol groups on Pd/SiO2 catalysed the acetalization of furfural and alcohol and the resulted acetal underwent hydrogenolysis on Pd nanoparticles (NPs) with an average particle size of 8 nm, leading to a moderate yield (∼58%) of furfuryl ethyl ether. Doping Na+ on Pd/SiO2 led to the diminishing of silanol groups as well as strong interaction between Na+ and Pd NPs. No acetalization occurred on Na+ modified Pd/SiO2 due to the exchange of H+ of Si-OH with Na+, thus the reductive etherification of C[double bond, length as m-dash]O group in furfural was completely inhibited. Meanwhile the hydrogenation of furan-ring over Na+ coordinated Pd NPs could proceed with very high selectivity (>90%) forming tetrahydrofurfural in high yield. Kinetics study on the hydrogenation of furfural diethyl acetal over Pd/SiO2 and Na+ doped Pd/SiO2 suggested that the Na+ greatly impeded the hydrogenolysis of C-O-C bond of acetal, while the hydrogenation of the furan ring took place selectively.

Synthesis of Ethyl-4-ethoxy Pentanoate by Reductive Etherification of Ethyl Levulinate in Ethanol on Pd/SiO2 -C Catalysts.

The synthesis of biomass-derived ethers to be used as biofuels or biofuel additives has attracted much attention. Following the recently reported synthesis of etherified ester ethyl-4-ethoxy pentanoate (EEP) from γ-valerolactone (GVL) in ethanol catalyzed by H-beta zeolite, an alternative route to prepare EEP in high yield has been developed by reductive etherification of ethyl levulinate (EL) in ethanol at 140 °C under 0.5 MPa H2 with a silica-modified Pd/C catalyst. The ether production likely follows a tandem acetalization-hydrogenolysis process with ethyl-4,4-diethoxy pentanoate (EDEP) as the intermediate. The acetalization step can be favored by introducing acidic materials, such as SiO2 -carbon or beta zeolite, as a cocatalyst. The combination of the Pd/SiO2 -C and beta zeolite mixture leads to 100 % EL conversion and 93 % EEP selectivity under optimized reaction conditions. For the first time, the standard molar combustion enthalpy of as-prepared EEP is measured by using a static oxygen bomb, and the value of which is determined to be about -5658 kJ mol-1 , which is much larger than that of GVL (-2650 kJ mol-1 ).

Controllably Confined ZnO on USY Zeolites (USY@ZnO/Al2 O3 ) as Efficient Lewis Acid Catalysts for Baeyer-Villiger Oxidation.

A ZnAl-LDHs (layered double hydroxides) phase was readily formed on the surface of a USY zeolite through a distinctive in situ growth method that benefitted from the interaction of the added Zn source and aluminum species extracted from the Al-rich USY zeolite crystals. The migration of aluminum and simultaneous interaction with the external Zn source took place in one pot to form a ZnAl-LDHs phase coated on the surface of the USY crystals. Upon calcination, the ZnAl-LDHs phase was transformed into a ZnO/Al2 O3 composite that was still firmly anchored on the USY zeolite, without sacrificing the core-shell structure. The resultant USY@ZnO/Al2 O3 materials gave rise to unique Lewis acidity and hierarchical porosity, which endowed the catalyst with promising performance in the Baeyer-Villiger oxidation of ketones with H2 O2 or bulky tert-butyl hydroxide as an oxidant.

At room temperature in water: efficient hydrogenation of furfural to furfuryl alcohol with a Pt/SiC-C catalyst.

Selective hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) is challenging because of many side reactions. The highly selective hydrogenation of FAL to FOL can be achieved over a Pt catalyst supported on nanoporous SiC-C composites even at room temperature in water. A Pt/SiC-C-200-H2 catalyst, which had a Pt loading of 3 wt% and was reduced in flowing hydrogen at 500 °C after calcination in air at 200 °C for 2 h, furnished complete FAL conversion and over 99% selectivity to FOL at 25 °C under 1 MPa of hydrogen in water. The kinetic behaviour of the selective hydrogenation of FAL to FOL with the 3 wt% Pt/SiC-C-200-H2 catalyst was also investigated and the turnover frequency (TOF) reached 1148 h-1. Moreover, the Pt/SiC-C catalyst is more active than other Pt catalysts supported on ordered mesoporous carbon CMK-3, activated carbon, periodic mesoporous silica SBA-15 or Al2O3. Detailed characterization using XRD, N2-sorption, SEM, TEM and XPS techniques reveals that the striking performance of the Pt/SiC-C catalyst can be attributed to the optimal metal-support interaction and the interfacial effect.

Robust synthesis of green fuels from biomass-derived ethyl esters over a hierarchically core/shell-structured ZSM-5@(Co/SiO2) catalyst.

A novel bifunctional ZSM-5@(Co/SiO2) material with a hierarchical core/shell structure was successfully prepared through a simple chemoselective interaction between the crystal surface silica species of zeolite and the external Co2+ source in basic media, which served as an excellent catalyst in the synthesis of green fuels from biomass-derived ethyl esters.

Aerobic oxidation of alcohols over hydrotalcite-supported gold nanoparticles: the promotional effect of transition metal cations.

Chromium (III)-containing hydrotalcites show strong synergy with gold nanoparticles in achieving high activity in the aerobic oxidation of alcohols.