The combination of cross polarization and magic-angle spinning (CP/MAS), is a routine technique for signal enhancement in solid-state nuclear magnetic resonance (NMR) spectrum. With CP/MAS, the acquisition efficiency of solid-state NMR experiments can be improved greatly. However, the enhanced signal is not quantitative according to the different CP dynamics dominated by several factors including heteronuclear dipolar couplings, spin-lattice relaxation times in the rotating frame, molecular motions, number of around abundant spins, and so on. Over the years, numerous efforts have been made to obtain quantitative CP/MAS spectroscopy. This review firstly briefly illustrated the introduction of CP and CP dynamics, and then a series of quantitative NMR methods based on CP were introduced, including ramped-amplitude CP (RAMP-CP), multiple-contact CP, quantification of CP (QCP), Lee-Goldburg frequency modulated CP (LG-FMCP) and quantitative CP (QUCP).

Monoclinic lithium vanadium phosphate is a promising cathode material for lithium-ion batteries, which has been widely studied in the past two decades. Solid-state nuclear magnetic resonance (SSNMR) is an excellent method to investigate the local environments of target nuclei and the short/long range structural changes of materials. In this short review, SSNMR studies on a few important aspects of monoclinic lithium vanadium phosphate, including charge-discharge mechanism, lithium mobility/dynamics, carbon coating, cation doping and theoretical calculation on NMR shifts, are briefly covered.

Carbon anode material is a traditional and widely-used anode material for lithium/sodium-ion batteries. However, it still has some drawbacks, such as long charging time and low columbic efficiency. Studying the charging and discharging mechanisms of the carbon anode material will help to solve these problems. Solid-state nuclear magnetic resonance (NMR) is an effective method to study the chemical environment of target atoms in solid materials and structural changes of materials. By measuring high speed magic-angle spinning (MAS) spectrum of ⁶Li, ⁷Li and ²³Na in lithium/sodium-ion batteries, the structural changes during the process of de-intercalation and coordination between the carbon atoms and Li/Na atoms can be elucidated. The information obtained can provide a sufficient theoretical basis for designing of novel carbon anode materials and improving their electrochemical properties. This paper reviews the application and progresses of solid-state NMR technology in the research of carbon anode materials for lithium/sodium-ion battery.

Cementitious materials have complex compositions and structures. Characterization of the hydration processes, and compositions and structure of productions of cementitious materials is challenging. One-dimensional solid-state nuclear magnetic resonance (NMR) is used to analyze the hydration degree of the binders (i.e., cement and mineral admixtures), as well as the species and structure of the hydration products (especially the non-crystal components), both qualitatively or quantitatively. Thereby, the effects of binder components, additives, and environment on the hydration process can be investigated. Two-dimensional NMR spectroscopy can provide further information on the connections between the same or different nuclei, confirming the presence of doping and substitution in the hydration products, as well as dispersion of organic additives in the matrix. It is concluded that solid-state NMR technology can be used to obtain information that rarely provided by other methods, and may advance the research on hydration process and microstructure of the cementitious materials.

With Ni/CeO₂ as an example, which has important applications in catalysis, ¹⁷O solid-state nuclear magnetic resonance (NMR) spectroscopy was applied to explore and analyze the concentration of surface Ni ions, according to the changes in the ¹⁷O NMR intensity of surface oxygen ions. The results indicate that the Ni concentrations in the first and second top metal ion layers in 10% NiCe-500 and 20% NiCe-300 are within the ranges of 9%~17% and 8%~15%, respectively. This approach may be extended to study the concentration of the doped paramagnetic elements in the surface for a variety of doped oxide materials.

Spin alignment echo (SAE) is employed here to study the α-LiAsF₆/PEO₆ system with low poly(ethylene oxide) (PEO) molecular weight. We show that the correlation rate k_SAE from SAE experiments, but not the spin-lattice relaxation time and the linewidth, is a better indicator to characterize the higher conductivity.

The tautomerism of organic molecules is widely observed in solution. While for solid organic chemicals, molecules often exist in the most stable tautomeric form. 2-Picolinic acid (PCA) is a very rare case which contains both the neutral molecules and zwitterions in the same crystal structure. Chemical shift assignment for PCA by experimental approach, e.g., 2D NMR methods, is extremely time consuming because the ¹H spin-lattice relaxation time (T₁) is too long. Density functional theory (DFT) calculation, especially using a periodic model, is an alternative protocol to fix this issue. However, the original crystal structure of PCA cannot be submitted directly for the calculation task due to the proton positional disorder. In this contribution, a virtual structure was constructed via crystallography approach. Theoretical ¹³C chemical shifts were obtained basing on this virtual model, which are consistent with the experimental values. Also, both neutral PCA and zwitterion demonstrated their featured chemical shifts, such information can be utilized to analyze the molecular states of PCA in its crystalline complexes.

Layered rare earth hydroxides are new classes of functional materials. In this study, a layered La(OH)₂NO₃ compound having both ion-exchange capacity and non-linear optical property was studied by solid-state nuclear magnetic resonance (SSNMR) spectroscopy. The quadrupolar Carr-Purcell-Meiboom-Gill sequence (QCPMG) was used to acquire ¹³⁹La SSNMR sub-spectra with variable offsets, from which the ultrawide-line spectrum was reconstructed by co-addition after applying a filtering function. The ultrawide-line spectrum consisted of both center and satellite transition line shapes, which were also simulated with the QUEST software. The ¹³⁹La C_Q and η_Q values measured by SSNMR experiments agreed well with those calculated with the Cambridge Sequential Total Energy Package (CASTEP). The ¹³⁹La SSNMR results unambiguously indicated that the layered La(OH)₂NO₃ compound studied belongs to a non-centrosymmetric space group of P2₁.

A series of silver-modified phosphotungstic acid catalysts Ag_xH_3-xPW₁₂O₄₀ (x=1, 2, 3) were synthesized by incorporating silver nitrate into phosphotungstic acid. The structure, stability and acidity of the catalysts synthesized were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis-derivative thermogravimetric analysis (TGA-DTG) and ³¹P-TMPO magic-angle spinning nuclear magnetic resonance (³¹P-TMPO MAS-NMR) spectroscopy. The effects of various reaction parameters, such as methanol/oil molar ratio, amount of catalyst, reaction time, and reaction temperature on the catalytic transesterification of soybean oil and methanol with Ag₂HPW₁₂O₄₀ were investigated. The results demonstrated that Ag₂HPW₁₂O₄₀ had the best catalytic activity, superior biodiesel yield and excellent durability. The high catalytic activity of the catalyst was attributed to Brønsted-Lewis acid synergy. With 6 wt.% Ag₂HPW₁₂O₄₀ catalyst, the yield of biodiesel reached 96.4% with a methanol/soybean oil molar ratio of 32/1, a reaction temperature of 150℃ and a reaction time of 20 h.

Structure and acidity changes of the acid sites in ultra-stable Y zeolites of different cell sizes during the hydrothermal aging process were studied by solid-state nuclear magnetic resonance (NMR) combined with molecular probes. The experimental results demonstrated that, during the initial stage of hydrothermal aging, parts of the framework aluminum species were removed from the framework and formed five-coordinate extra-framework aluminum species. In the meanwhile, the five-coordinate extra-framework aluminum species migrated to the surface and formed poly-aluminum species, resulting in decreases of both Brønsted acid sites and Lewis acid sites. The acidity of ultra-stable Y zeolites changed considerably during the first 3 h of the aging process, and the change of Brønsted acid content was proportional to the unit cell dimension of the fresh zeolites agent. With the increase of aging time, the aluminum distribution tended to become stable, with little further changes in the amounts of Brønsted acid and Lewis acid sites. The synergy between Brønsted/Lewis acids in the ultra-stable Y zeolites existed during the entire aging process, resulting in a stably enhanced acidity for the Brønsted acid sites.

In this paper, the effects of reaction environment (ambient atmosphere, pressure, gas quantity etc.) on the photocatalytic methanol reforming reaction were studied systematically in a real reaction system using operando nuclear magnetic resonance spectroscopy. It was shown that the ambient atmosphere had differential inhibitory effects on the yields of reaction products, while the environmental pressure and gas quantity had little influences. Based on these observations, the adsorption modes of gases on the catalyst surface were investigated, and a mechanism through which the ambient atmosphere affected the photocatalytic reforming process of methanol was proposed.

Spin polarized ³He is widely used to polarize neutrons as neutron spin filters (NSF). China Mianyang Research Reactor (CMRR) has established the first spin exchange optical pumping (SEOP) polarized ³He neutron polarization system in China. In order to monitor the relative change in the polarizability of ³He as a function of time, a ³He polarimetry system based on nuclear magnetic resonance (NMR) was designed and implemented, with which the ³He polarizability could be monitored regularly using Matlab programs. The configuration and signal-to-noise ratio (SNR) of the pickup coil were optimized. It was shown that, for a given length of winding wire, the design of a Brooks coil could improve the SNR, and achieve maximal SNR when the average radius of the coil set to (a₀+d)/√2, where a₀ is the radius of ³He cell, and d is the distance between the pickup coil and the cell. The noise floor level of the system was also measured, and shown to be dominated by environment noise (0.27 μV/√Hz) and data acquisition (DAQ) card noise (0.40 μV/√Hz). The power spectral density of the system was found to be approximately √0.16+0.073G² μV/√Hz, where G is the gain of the amplifier.

The background ¹³C NMR signal originated from the organic materials in the probe head cross-polarizes from ¹H nucleus to ¹³C nucleus. This background ¹³C NMR signal is very broad (δ_C 20~250) and accumulates as the sample signal accumulating. Hartman-Hahn cross polarization with phase-incremented pulses in the S spin channel (denoted as PIPCP) is developed to suppress this background signal. The application of PIPCP results in severe phase distortion outside the radio frequency coil such that the background ¹³C NMR signal cannot cross polarize and thus be suppressed. In comparison, depending on the dipolar coupling constant between ¹H and ¹³C nuclei, PIPCP induces only a small amount of Hartman-Hahn mismatch (1.4%) to the desired signals.