Unraveling the atomic structure and dissociation of interfacial water on anatase TiO (101) under ambient conditions with solid-state NMR spectroscopy.

Anatase TiO is a widely used component in photo- and electro-catalysts for water splitting, and the (101) facet of anatase TiO is the most commonly exposed surface. A detailed understanding of the behavior of HO on this surface could provide fundamental insights into the catalytic mechanism. This, however, is challenging due to the complexity of the interfacial environments, the high mobility of interfacial HO, and the interference from outer-layer HO.

Atomically Dispersed Nickel Anchored on a Nitrogen-Doped Carbon/TiO Composite for Efficient and Selective Photocatalytic CH Oxidation to Oxygenates.

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO composite (Ni-NC/TiO ) as a highly active and selective catalyst for photooxidation of CH to C1 oxygenates with O as the only oxidant.

Efficient and selective photocatalytic CH conversion to CHOH with O by controlling overoxidation on TiO.

The conversion of photocatalytic methane into methanol in high yield with selectivity remains a huge challenge due to unavoidable overoxidation. Here, the photocatalytic oxidation of CH into CHOH by O is carried out on Ag-decorated facet-dominated TiO. The {001}-dominated TiO shows a durable CHOH yield of 4.

Through-space B- Al correlation: Influence of the recoupling channel.

Through-space heteronuclear correlation (D-HETCOR) experiments based on heteronuclear multiple-quantum correlation (D-HMQC) and refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT) sequences have been proven to be useful approaches for the detection of the spatial proximity between half-integer quadrupolar nuclei in solids under magic-angle spinning (MAS) conditions. The corresponding pulse sequences employ coherence transfers mediated by heteronuclear dipolar interactions, which are reintroduced under MAS by radiofrequency irradiation of only one of the two correlated nuclei. We investigate herein using numerical simulations of spin dynamics and solid-state NMR experiments on magnesium aluminoborate glass how the choice of the channel to which the heteronuclear dipolar recoupling is applied affects the transfer efficiency of D-HMQC and D-RINEPT sequences between B and Al nuclei.

Metal Nanoparticles Confined within an Inorganic-Organic Framework Enable Superior Substrate-Selective Catalysis.

The search for catalysts with a perfect substrate selectivity toward the hydrogenation of nitroarenes is a goal of high importance, which still remains a significant challenge. Here, we designed a new type of catalyst with superior substrate selectivity by combining a space-confined effect and a hydrogen-bonding network, in which metal nanoparticles (MNPs) were confined in hierarchical hollow silica (HHS) with a poly(-isopropylacrylamide) (PNIPA) coating. Given the strong induced properties of hydrogen-bond donors and acceptors in the HHS support and PNIPA coating, the as-synthesized catalyst would achieve perfect substrate selectivity for the hydrogenation of various nitroarenes and their mixture by thoroughly impeding the reduction of nitroarenes with any hydroxyl or carboxyl groups, which is typically very difficult to be realized over almost all of the reported supported-metal catalysts.

The acidic nature of "NMR-invisible" tri-coordinated framework aluminum species in zeolites.

The unambiguous characterization of different acid sites in zeolites is of great importance for understanding their catalytic performance and the rational design of highly efficient zeolite catalysts. In addition to various well-characterized extra-framework Al species, a tri-coordinated framework aluminum species can also serve as a Lewis acid site in zeolites, which is "NMR-invisible" owing to its extremely distorted local environment. Here we provide a feasible and reliable approach to elucidate the acidic nature of the tri-coordinated framework Al in dehydrated H-ZSM-5 zeolites sensitivity-enhanced two-dimensional (2D) multiple nuclear correlation NMR experiments coupled with trimethylphosphine oxide (TMPO) probe molecules.

Observation of an oxonium ion intermediate in ethanol dehydration to ethene on zeolite.

Zeolite-catalyzed dehydration of ethanol offers promising perspectives for the sustainable production of ethene. Complex parallel-consecutive pathways are proposed to be involved in the reaction network of ethanol dehydration on zeolites, where the initial step of ethanol dehydration is still unclear particularly for the favorable production of ethene at lower temperature. Here we report the observation of a triethyloxonium ion (TEO) in the dehydration of ethanol on zeolite H-ZSM-5 by using ex situ and in situ solid-state NMR spectroscopy.

Control of Spatially Homogeneous Distribution of Heteroatoms to Produce Red TiO Photocatalyst for Visible-Light Photocatalytic Water Splitting.

The strong band-to-band absorption of photocatalysts spanning the whole visible-light region (400-700 nm) is critically important for solar-driven photocatalysis. Although it has been actively and widely used as a photocatalyst for various reactions in the past four decades, TiO has a very poor ability to capture the whole spectrum of visible light. In this work, by controlling the spatially homogeneous distribution of boron and nitrogen heteroatoms in anatase TiO microspheres with a predominance of high-energy {001} facets, a strong visible-light absorption spectrum with a sharp edge beyond 680 nm has been achieved.

Uniform signal enhancement in MAS NMR of half-integer quadrupolar nuclei using quadruple-frequency sweeps.

We introduce two MAS schemes that allow manipulating the satellite-transition (ST) populations of half-integer quadrupolar nuclei, and which both exhibit improved robustness to the quadrupolar coupling constant (C). These schemes, called quadruple frequency sweep (QFS) or quadruple WURST (QWURST) are the sums of two DFS or four WURST to efficiently invert the ST populations of nuclei subject to large or small quadrupole interactions, simultaneously. These quadruple sweeps methods only require 6% more rf-power than the double sweeps ones.

Transfer Channel of Photoinduced Holes on a TiO Surface As Revealed by Solid-State Nuclear Magnetic Resonance and Electron Spin Resonance Spectroscopy.

The detailed structure-activity relationship of surface hydroxyl groups (Ti-OH) and adsorbed water (HO) on the TiO surface should be the key to clarifying the photogenerated hole (h) transfer mechanism for photocatalytic water splitting, which however is still not well understood. Herein, one- and two-dimensional H solid-state NMR techniques were employed to identify surface hydroxyl groups and adsorbed water molecules as well as their spatial proximity/interaction in TiO photocatalysts. It was found that although the two different types of Ti-OH (bridging hydroxyl (OH) and terminal hydroxyl (OH) groups were present on the TiO surface, only the former is in close spatial proximity to adsorbed HO, forming hydrated OH.

Heteronuclear correlation experiments of Na-Al in rotating solids.

We demonstrated that the heteronuclear correlation experiments between two quadrupolar nuclei, Na and Al, with close Larmor frequencies can be achieved via D-HMQC and D-RINEPT approaches by using a diplexer connected to a conventional probe in magic-angle-spinning solid-state NMR. Low-power heteronuclear dipolar recoupling schemes can be applied on Na or Al to establish polarization transfers between the central transitions of Na and Al for a model compound, NaAlO. Further, we showed a practical implementation of the two dimensional Na-Al dipolar-based heteronuclear correlation experiment on a heterogeneous catalyst, NaCO/γ-AlO.

Unravelling the Efficient Photocatalytic Activity of Boron-induced Ti Species in the Surface Layer of TiO.

Ti species are highly unstable in air owing to their facile oxidation into Ti species, and thus they cannot concentrate in the surface layer of TiO but are mainly present in its bulk. We report generation of abundant and stable Ti species in the surface layer of TiO by boron doping for efficient utilization of solar irradiation. The resultant photocatalysts (denoted as B-TiO) exhibit extremely high and stable solar-driven photocatalytic activity toward hydrogen production.

Direct Detection of Supramolecular Reaction Centers in the Methanol-to-Olefins Conversion over Zeolite H-ZSM-5 by (13)C-(27)Al Solid-State NMR Spectroscopy.

Hydrocarbon-pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon-pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H-ZSM-5 zeolite by advanced (13)C-(27)Al double-resonance solid-state NMR spectroscopy.

Experimental Evidence on the Formation of Ethene through Carbocations in Methanol Conversion over H-ZSM-5 Zeolite.

The methanol to olefins conversion over zeolite catalysts is a commercialized process to produce light olefins like ethene and propene but its mechanism is not well understood. We herein investigated the formation of ethene in the methanol to olefins reaction over the H-ZSM-5 zeolite. Three types of ethylcyclopentenyl carbocations, that is, the 1-methyl-3-ethylcyclopentenyl, the 1,4-dimethyl-3-ethylcyclopentenyl, and the 1,5-dimethyl-3-ethylcyclopentenyl cation were unambiguously identified under working conditions by both solid-state and liquid-state NMR spectroscopy as well as GC-MS analysis.

Population transfer HMQC for half-integer quadrupolar nuclei.

This work presents a detailed analysis of a recently proposed nuclear magnetic resonance method [Wang et al., Chem. Commun.

Direct visualization of a guest-triggered crystal deformation based on a flexible ultramicroporous framework.

Host-guest composites may exhibit abnormal and/or controllable physical properties that are unavailable for traditional solids. However, it is still very difficult to control or visualize the occupancy and motion of the guest. Here we report a flexible ultramicroporous coordination polymer showing exceptional guest-responsive thermal-expansion properties.

Signal enhancement of J-HMQC experiments in solid-state NMR involving half-integer quadrupolar nuclei.

We show that for half-integer quadrupolar nuclei, the manipulation of the satellite transitions can accelerate and enhance coherence transfer to other isotopes. This novel strategy is demonstrated to improve the sensitivity of (31)P-{(27)Al} J-HMQC experiments for a layered aluminophosphate Mu-4.

Understanding the high photocatalytic activity of (B, Ag)-codoped TiO2 under solar-light irradiation with XPS, solid-state NMR, and DFT calculations.

The origin of the exceptionally high activity of (B, Ag)-codoped TiO(2) catalysts under solar-light irradiation has been investigated by XPS and (11)B solid-state NMR spectroscopy in conjunction with density functional theory (DFT) calculations. XPS experimental results demonstrated that a portion of the dopant Ag (Ag(3+)) ions were implanted into the crystalline lattice of (B, Ag)-codoped TiO(2) and were in close proximity to the interstitial B (B(int.)) sites, forming [B(int.

New insights into Keggin-type 12-tungstophosphoric acid from 31P MAS NMR analysis of absorbed trimethylphosphine oxide and DFT calculations.

The acid and transport properties of the anhydrous Keggin-type 12-tungstophosphoric acid (H(3)PW(12)O(40); HPW) have been studied by solid-state (31)P magic-angle spinning NMR of absorbed trimethylphosphine oxide (TMPO) in conjunction with DFT calculations. Accordingly, (31)P NMR resonances arising from various protonated complexes, such as TMPOH(+) and (TMPO)(2)H(+) adducts, could be unambiguously identified. It was found that thermal pretreatment of the sample at elevated temperatures (≥423 K) is a prerequisite for ensuring complete penetration of the TMPO guest probe molecule into HPW particles.