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By fitting observed data with predicted seismograms, least‐squares migration (LSM) computes a generalized inverse for a subsurface reflectivity model, which can improve image resolution and reduce artifacts caused by incomplete acquisition. However, the large computational cost of LSM required for simulations and migrations limits its wide applications for large‐scale imaging problems. Using point‐spread function (PSF) deconvolution, we present an efficient and stable high‐resolution imaging method. The PSFs are first computed on a coarse grid using local ray‐based Gaussian beam Born modeling and migration. Then, we interpolate the PSFs onto a fine‐image grid and apply a high‐dimensional Gaussian function to attenuate artifacts far away from the PSF centers. With 2D/3D partition of unity, we decompose the traditional adjoint migration results into local images with the same window size as the PSFs. Then, these local images are deconvolved by the PSFs in the wavenumber domain to reduce the effects of the band‐limited source function and compensate for irregular subsurface illumination. The final assembled image is obtained by applying the inverse of the partitions for the deconvolved local images. Numerical examples for both synthetic and field data demonstrate that the proposed PSF deconvolution can significantly improve image resolution and amplitudes for deep structures, while not being sensitive to velocity errors as the data‐domain LSM. Plain Language Summary: Seismic imaging is an important tool to detect hydrocarbon resource and study deep Earth's structure. Traditional ray‐based and wave equation imaging methods commonly extrapolate observed data and apply appropriate imaging condition to construct subsurface impedance interfaces. Mathematically, these methods can be considered as adjoint operators of seismic modeling, but they have difficulty to produce high‐quality images of complicated subsurface structures. To mitigate this issue, we present an efficient and stable high‐resolution imaging approach, i.e., the point‐spread function (PSF) deconvolution. The locally temporal and spatial limitations are utilized to efficiently compute the PSFs on a coarse grid using a ray‐based Gaussian beam propagator. Then, an on‐the‐fly interpolation on a fine grid and a wavenumber‐domain deconvolution are applied to improve image resolution. Numerical experiments for benchmark model and field data demonstrate the feasibility and adaptability of the proposed method for imaging complicated salt structure and low‐signal‐to‐noise data. Key Points: Conventional least‐squares migration is too expensive to be widely applied for large‐scale problems under current computational capacityAn efficient approach for calculating point‐spread functions using local modeling and migration is proposedThe point‐spread function deconvolution is then applied to incorporate the Hessian effect and improve image quality [ABSTRACT FROM AUTHOR]

This study explored the effects of Ti3SiC2 on the microstructure and properties of laser cladding coatings using X-ray diffractometer, scanning electron microscope, electrochemical workstation, and UMT-2 wear tester analyses. It was found that with the addition of Ti3SiC2, the reinforcing phases in the composite coating were TiC, Ti(B,C)2, honeycomb-like (Cr, Fe)23C6, and a novel composite ceramic with an "eyeball" structure, which had an inside core of Al2O3 and TiC outer surrounding structure. The microhardness, wear, and corrosion resistance of the composite coating were about 1.35, 2, and 4.3 times those of the original coating, respectively. The main wear mechanisms of the original coating were severe fatigue spalling and microcutting, while the main mechanisms of the composite coating were slight microcutting and the formation of the transferred film. [ABSTRACT FROM AUTHOR]

Ray theory gives a high‐frequency asymptotic solution of the wave equation, which has been widely used in the seismic study because of its high computational efficiency and good physical insights for elementary waves. However, the fundamental high‐frequency assumption makes it difficult to accurately simulate the finite‐frequency effect of wave propagations. On the other hand, the Gaussian beam, as one of the advanced ray‐based methods, overcomes the amplitude singularity problem near the caustics by introducing a complex‐valued paraxial approximation. But Gaussian beams only use the velocity and up to second‐order velocity derivative of central rays and thus does not accurately simulate the response of heterogeneity away from the rays. To bridge the gap between the ray theory and wave‐equation methods, we present a two‐way beam wave method and apply it to seismic imaging. A fan of central rays are first shot to extract local ray‐centered model parameters in the global Cartesian coordinates. Then, a finite‐difference method is used to solve the acoustic wave equation in the ray‐centered coordinates to simulate wave propagations near the central rays. The beam wave method can accurately simulate the response of the velocity heterogeneities in the ray tubes and therefore produces more accurate wavefields. In addition, we discretize the ray‐centered wave equation onto a non‐orthogonal grid, which considerably reduces the computational cost. We apply the two‐way beam wave method in seismic imaging and develop a beam wave reverse‐time migration. It inherits the advantages of both ray‐based and wave equation migrations, and produces clear images for complicated structures with fewer artifacts than traditional imaging methods. Plain Language Summary: Seismic ray theory has evolved from classical asymptotic ray theory, through paraxial ray theory and Maslov's method, and then to the Gaussian beam method. Although the computational accuracy of the ray‐based methods for seismic modeling and imaging have been greatly improved, the fundamental high‐frequency approximation still prevents them from accurately describing finite‐frequency wave propagations in complex structures. We introduce the idea of reverse‐time migration into the beam method and develop a two‐way beam wave scheme for seismic modeling and imaging. Local velocities in the vicinity of central rays are first extracted and then the finite‐difference approach is used to solve the wave equation in the ray‐centered coordinate. Accurate wavefield simulation and beam‐to‐beam imaging condition enables us to achieve clear migrated images with fewer artifacts than traditional Gaussian beam migration and reverse‐time migration. Numerical examples for benchmark models and field data demonstrate the feasibility and adaptability of the proposed two‐way beam wave method. Key Points: It is difficult for ray theory to accurately simulate seismic wave phenomena in areas with strong velocity variationsA two‐way beam wave method is proposed to bridge the gap between ray‐based and wave equation approachesA beam wave reverse‐time migration approach is developed to improve the image quality for complicated subsurface environments [ABSTRACT FROM AUTHOR]

Classic L2-norm-based waveform tomography is often plagued by insurmountable cycle skipping problems; as a result, the iterative inversion falls into local minima, yielding erroneous images. According to the optimal transportation theory, we adopt a novel geometry-preserving misfit function based on the quadratic Wasserstein metric (W2-norm), which improves the stability and convexity of the inverse problem. Numerical experiments illustrate that W2-norm-based full-waveform tomography has a larger convergence radius and a faster convergence rate than the L2-norm and can effectively mitigate cycle skipping issues. We apply this method to the Longmen Shan area and obtain a reliable lithospheric velocity model. Our tomographic results indicate that the crystalline crust underlying the Sichuan Basin wedges into the crustal interior of the Tibetan Plateau, and the mid-lower crust of the eastern Tibetan Plateau is characterized by low shear-wave velocities, indicating that ductile crustal flow and strong interactions between terranes jointly dominate the uplift behavior of the Longmen Shan. Furthermore, we find that large earthquakes (e.g., the Wenchuan and Lushan events) occur not only at the junction between high- and low-velocity regions but also in the transition zone from positive to negative radial anisotropy. These findings improve our understanding of the mechanism responsible for large earthquakes in this region. [ABSTRACT FROM AUTHOR]

Locating micro-earthquakes with high resolution and accuracy is a challenge for traveltime inversion, which has uncertainty on the order of a Fresnel zone (many wavelengths). We develop a wave-equation imaging method to increase resolution and reduce location errors to less than a wavelength, but requires very densely deployed receiver arrays with wide aperture and considerable computational cost. Instead of using acoustic data or direct P wave arrivals only, we use elastic multicomponent data and present a new method that uses the full P and S adjoint wavefields to image the microseismic source locations. We separate the P and S waves from the data, and extrapolate the P and S wavefields of each receiver subarray by solving the P and S adjoint wave equations in parallel. We formulate three source imaging conditions by multiplying over subarrays the adjoint P wavefield (I P), S wavefield (I S) and cross-correlated P and S wavefields (I PS). We perform numerical experiments on the highly realistic SEG SEAM4D reservoir model using surface acquisition array geometries. Results for 2-D and 3-D microseismic source estimations show clean images without noisy artefacts at shallow depths. In particular, I PS provides the highest resolution source location image, while I P is limited by the P wavelength and I S is influenced by small coda artefacts. The major-axis alignment and resolution of the source location image are determined by the hypocentral location with respect to the receiver array and illumination-angle coverage, respectively. We discuss the impacts of S -wave attenuation and frequency bandwidth on the source location images. Noise tests indicate that the imaging results are relatively insensitive to ambient noise, as is observed for the surface monitoring data. Using smoothed velocity models, the imaging results are similar to the results using the true realistically heterogeneous velocity model. The 90 per cent confidence ellipse of the source location due to Gaussian-distributed velocity errors shows a larger depth error as the source becomes deeper, while the horizontal error does not change as much. [ABSTRACT FROM AUTHOR]

Sparse representation and inversion have been widely used in the acquisition and processing of geophysical data. In particular, the low-rank representation of seismic signals shows that they can be determined by a few elementary modes with predominantly large singular values. We review global and local low-rank representation for seismic reflectivity models and then apply it to least-squares migration (LSM) in acoustic and viscoacoustic media. In the global singular value decomposition (SVD), the elementary modes determined by singular vectors represent horizontal and vertical stratigraphic segments sorted from low to high wavenumbers, and the corresponding singular values reflect the contribution of these basic modes to form a broadband reflectivity model. In contrast, local SVD for grouped patch matrices can capture nonlocal similarity and thus accurately represent the reflectivity model with fewer ranks than the global SVD method. Taking advantage of this favorable sparsity, we introduce a local low-rank regularization into LSM to estimate subsurface reflectivity models. A two-step algorithm is developed to solve this low-rank constrained inverse problem: the first step is for least-squares data fitting and the second is for weighted nuclear-norm minimization. Numerical experiments for synthetic and field data demonstrate that the low-rank constraint outperforms conventional shaping and total-variation regularizations, and can produce high-quality reflectivity images for complicated structures and low signal-to-noise data. [ABSTRACT FROM AUTHOR]

The pseudo-differential operator with symbol | k |α has been widely used in seismic modelling and imaging when involving attenuation, anisotropy and one-way wave equation, which is usually calculated using the pseudo-spectral method. For large-scale problems, applying high-dimensional Fourier transforms to solve the wave equation that includes pseudo-differential operators is much more expensive than finite-difference approaches, and it is not suitable for parallel computing with domain decomposition. To mitigate this difficulty, we present a truncated space-domain convolution method to efficiently compute the pseudo-differential operator |$\sqrt{-\nabla ^2}$|⁠ , and then apply it to viscoacoustic reverse-time migration. Although |$\sqrt{-\nabla ^2}$| is theoretically non-local in the space domain, we take the limited frequency band of seismic data into account, and constrain the approximated convolution stencil to a finite length. The convolution coefficients are computed by solving a least-squares inverse problem in the wavenumber domain. In addition, we exploit the symmetry of the resulting convolution stencil and develop a fast spatial convolution algorithm. The applications of the proposed method in Q -compensated reverse-time migration demonstrate that it is a good alternative to the pseudo-spectral method for computing the pseudo-differential operator |$\sqrt{-\nabla ^2}$|⁠ , with almost the same accuracy but much higher efficiency. [ABSTRACT FROM AUTHOR]

High-precision ages of Cenozoic volcanic rocks in northeast China are widely reported recently. However, the systematic analysis of spatio-temporal distribution of Cenozoic volcanism, which is important for reconstructing and constraining regional tectonic evolution, is still limited. Here, we collected published geochronological data from more than 400 Cenozoic volcanic samples in northeast China. Combined with field observations of volcanic rock samples and three valid 40Ar-39Ar geochronological data obtained in this study, we compile geochronological data in northeast China and explore a new spatio-temporal distribution pattern for the Cenozoic volcanism in order to constrain geodynamic models for northeast China. Our results show that the Cenozoic volcanism in northeast China has a horseshoe-shaped distribution, and the volcanism almost existed from Paleocene to Quaternary, which can be roughly divided into six volcanic belts. Our results suggest that the volcanism in this region is centred on around the Songliao Basin, then migrates eastward, and eventually has end up with a series of intense activity around the Songliao Basin. This may be related to the upwelling of the asthenosphere caused by the subduction of the Pacific plate and the opening of the Japan Sea. Our study also reveals that Chuandishan basalt in Dunhua area formed by Early Oligocene volcanic activity, which differs from the Pliocene or Miocene stratigraphic ages assumed before. [ABSTRACT FROM AUTHOR]

Real-time positioning of a specific object in the big data environment can improve the monitoring and management capacity for network data. For the real-time positioning of the specific object, it is necessary to quickly search the network data representing a specific object and match its pattern strings and compare the corresponding Internet protocol (IP) address of the matched network data with the IP address library in real time, so as to determine the position of the specific object. When a traditional method is used for pattern string matching, it will occupy a lot of memories and network resources, thereby reducing the positioning effect of the specific object in the big data environment. A positioning method for a specific object of high performance and multi-pattern matching based on three indexes in the big data network environment is proposed in this paper. Firstly, the initialization of Modified Wu-Manber (MWM) algorithm was carried out, and the algorithm was used to match the network data continuously. Secondly, the three indexes were used to improve the MWM algorithm, and the real-time and fast positioning of a specific object in the big data environment was completed by the Third Index Modified Wu-Manber (TMWM). The experimental results show that compared with the traditional method, the proposed algorithm reduces the pattern string matching scope of network data representing the specific object, improves the search speed of the specific object, and locates the specific object in the big data environment in an effective and rapid manner. [ABSTRACT FROM AUTHOR]

Different bimetallic platinum and bismuth catalysts supported on melamine‐modified activated carbon (AC) are designed by a co‐impregnation method. Through controlling the activation temperatures of the melamine−AC mixture, a series of N‐doped and C3N4‐modified AC (N−AC and C3N4−AC) are prepared. Combined powder X‐ray diffractions, X‐ray photoelectron spectroscopic, and high‐angle annual dark‐field scanning transmission electron microscopic studies demonstrate that the introduction of C3N4 favors the formation of PtBi alloy and leads to increased particle sizes in comparison to the pristine and N‐doped AC‐supported bimetallics. The catalytic performance of the developed catalysts is evaluated in the oxidation of n‐heptanol oxidation in a batch mode using O2 as the oxidant. PtBi/C3N4−AC exhibits significantly boosted activity as well as selectivity to heptanoic acid as compared with the other catalysts. A high yield of heptanoic acid of 69 % can be achieved under the optimized reaction conditions. Furthermore, our work points to the PtBi alloy as the most active sites for the alcohol oxidation. Catalyst deactivation occurs in the cycling tests, mainly due to the collapse of the alloy phase and likely the decrease in particle sizes. [ABSTRACT FROM AUTHOR]

In this study, we reported an efficient heterogeneous nanocatalyst Pd°-PyPPh 2 @POP catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without using extra hydrogen acceptors and inorganic base additives. [Display omitted] • A highly dispersed palladium nanoparticle catalyst was prepared using bifunctional porous organic polymer as support. • The Pd°-PyPPh 2 @POP catalyst exhibited high activity without extra hydrogen acceptors and inorganic base additives. • The Pd°-PyPPh 2 @POP catalyst exhibited higher activity than the corresponding inorganic material supported catalyst. In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh 2 @POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh 2 @POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh 2 @POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh 2 @POP polymer are themselves used as solid base over the Pd°-PyPPh 2 @POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K 2 CO 3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts. [ABSTRACT FROM AUTHOR]

Selective synthesis of mixed alcohols from syngas (CO + H 2 ) via Fischer–Tropsch synthesis (FTS) is an alternative one-step one-pot method. Here we report a series of Co-based catalysts supported by activated carbon (AC) and promoted by Mn and La, namely, Co x Mn y La/AC, over which the selectivity to alcohols is usually ∼26.8% and up to 31.7% at elevated reaction pressure, accompanied by a large amount of olefin byproducts (∼30%) that can be further converted to alcohols via a hydroformylation process. Detailed characterizations are performed for the structural properties of catalysts, including physisorption, chemisorption, microscopy, crystal structure, and surface element compositions. The active site of Co x Mn y La/AC catalysts is the highly dispersed metallic Co on the surface of Co 2 C nanoparticles (Co@Co 2 C), similar to that of Co x Mn/AC catalysts reported previously, while that of Co y La/AC catalysts is a combination of metallic Co and Co 2 C phases (Co–Co 2 C). The result indicates that Mn promoter plays a determinative role in the formation of active sites over Co x Mn y La/AC catalysts. Nevertheless, the La promoter tends to aggregate on the surface of cobalt nanoparticles in the form of La 2 O 3 to promote the CO insertion step and enhance the H 2 chemisorption, so that it can both facilitate the formation of alcohols and make the FTS product class shift to light components. The result proves that the structure of active sites can be established by adding a strong promoter such as Mn, and a second promoter, such as La, can be used to tune the FTS reaction toward alcohols by further modifying its surface properties. [ABSTRACT FROM AUTHOR]

Significant imbalances in terrestrial water storage (TWS) and severe drought have been observed around the world as a consequence of climate changes. Improving our ability to monitor TWS and drought is critical for water‐resource management and water‐deficit estimation. We use continuous seismic ambient noise to monitor temporal evolution of near‐surface seismic velocity, dv/v, in central Oklahoma from 2013 to 2022. The derived dv/v is found to be negatively correlated with gravitational measurements and groundwater depths, showing the impact of groundwater storage on seismic velocities. The hydrological effects involving droughts and recharge of groundwater occur on a multi‐year time scale and dominate the overall derived velocity changes. The thermoelastic response to atmospheric temperature variations occurs primarily on a yearly timescale and dominates the superposed seasonal velocity changes in this study. The occurrences of droughts appear simultaneously with local peaks of dv/v, demonstrating the sensitivity of near‐surface seismic velocities to droughts. Plain Language Summary: Terrestrial water storage (TWS) is fundamental to the well‐being of inhabitants on Earth. However, current approaches to measure TWS variations have limited temporal or spatial resolution. In this study, we use near‐surface seismic velocity variations, dv/v, derived from continuous seismic recordings to monitor changes of TWS in central Oklahoma. A negative correlation between the long‐term trend of dv/v with gravity measurements reflects the impact of groundwater recharge/discharge on near‐surface seismic velocity. In addition, a seasonal cycling of dv/v has similar periodicity to recordings of air temperature, which can be explained by thermo‐elastic strain at the subsurface. Comparisons between dv/v and drought index further show the possibility of using near‐surface seismic velocity as a proxy for monitoring severe drought for local communities. Considering the high temporal sampling and flexible spatial deployment, seismometers may be used to monitor subsurface water distributions. This can be useful for sustainable water management and reliable water‐deficit estimation. Key Points: A long‐term trend of dv/v in Oklahoma correlates well with gravity measurements, which may reflect groundwater recharge and dischargeShort‐term peaks of dv/v agree with the drought index, demonstrating a potential for monitoring meteorological droughtsA seasonal cycle of dv/v in central Oklahoma can be explained by thermo‐elastic strains driven by atmospheric temperature changes [ABSTRACT FROM AUTHOR]

The acoustic behavior in fluid attenuating media can be effectively simulated using a fractional Zener model (FZM). Because of the fractional time derivatives of both stress and strain in the constitutive relationship, this mechanism is very realistic and flexible in describing seismic attenuation. However, using conventional FZM wave equations to propagate seismic waves requires storing large amounts of previous wavefield information to calculate the fractional time derivatives, which is unacceptable in practice. In this paper, we derive a new time-domain viscoacoustic wave equation in the framework of the FZM. This new equation does not contain any fractional time derivatives; thus, it is more economical in computational costs. Furthermore, the amplitude attenuation and phase dispersion effects are separated in the newly proposed equation, which is very favorable to compensate for energy loss and correct phase dispersion in reverse-time migration. To improve the accuracy, we incorporate a wave number (k)-space operator into the decoupled FZM wave equation to compensate for temporal dispersion errors caused by the second-order finite-difference discretization. Therefore, a high-temporal-accuracy viscoacoustic wave equation is derived to simulate nearly constant-Q wavefields in attenuating media. In the implementation, a low-rank decomposition method is introduced to solve the mixed-domain operators. Numerical analysis and modeling results demonstrate the effectiveness and applicability of the proposed method for simulating the decoupled viscoacoustic wavefield with high accuracy. [ABSTRACT FROM AUTHOR]

SUMMARY: It has been widely recognized that seismic attenuation and dispersion can be induced by various mechanisms. Wave induced fluid flow (WIFF) is one of the popular mechanisms to interpret seismic wave attenuation and dispersion, especially at microscopic scale. In this study, we focus on the local flow induced by different compliances of adjacent pores and develop a unified model called BISSQ (Biot-spherical squirt) model based upon the Biot and spherical squirt flow theories. The proposed model is an extension of BISQ (Biot-squirt) model. The P -wave velocity and attenuation of BISSQ model are influenced by two mechanisms: the Biot and spherical squirt-flow mechanisms. To evaluate the impact of these two mechanisms on seismic wave propagation, we use different parameters (e.g. squirt flow length, fluid viscosity, permeability, saturation and so on) to simulate wave attenuation and dispersion. We then apply the proposed model to Fox Hills Sandstone, which shows that the model can realistically predict P -wave velocity dispersion. To sum up, our proposed model offers an alternative squirt flow attenuation mechanism, which can describe fluid state of squirt flow reasonably and help us to assess the effect of different parameters on seismic wave attenuation. [ABSTRACT FROM AUTHOR]

The influence of AlO promoter on a performance of C-C α-alcohols direct synthesis from syngas over activated carbon (AC) supported cobalt catalysts (Co/AC catalysts) was investigated using CO hydrogenation evaluation, XRD, HRTEM, H-TPR, pulsed CO chemisorption, H-TPD and N physisorption techniques. The results obtained showed that the addition of AlO increased significantly the Co component dispersion without remarkably decreasing its reducibility and inhibited its aggregation during reaction, resulting in greatly enhanced reaction activity as well as increased selectivity towards liquid products. Appropriate amounts of AlO can promote the formation of CoC, leading to an increase of total alcohol fraction in the liquid products. Moreover, the AlO addition can further promote the formation of higher alcohols (C-C alcohols). Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The Midcontinent Rift (MCR), hosting several world-class ore deposits, is the fossil remnant of a massive Mesoproterozoic rifting event (1.1 Ga) that did not lead to the formation of an ocean basin. To better understand the lithospheric processes associated with the rifting stage and its subsequent failure, we developed a novel full-waveform joint inversion method using ambient noise data and teleseismic P waves for this seismically inactive region. We apply this approach to three years (2011-2013) of seismic recordings from the Superior Province Rifting EarthScope Experiment (SPREE) (~12 km average station spacing) and the USArray Transportable Array (~70 km average station spacing), and obtain a new 3D high-resolution Vs model down to 100 km depth, as well as Vp and density models down to 60 km depth. The model shows major velocity anomalies in agreement with previous seismic studies for the western arm of the MCR. In particular, we observe high density (2.8-3.0 g/cm3), Vp (6.3-6.5 km/s), and Vs (3.6-3.7 km/s) structures in the shallow upper crust within the rift, likely associated with volcanic rocks. Similar to a previously identified underplated layer, we also observe extensive normal-to-high Vs (3.8-4.2 km/s) along the whole rift axis and Vp (6.8-7.5 km/s) beneath the northern segment of the rift within the lower crust. However, the Vs and Vp values are lower than average for typical underplated materials. We suggest that this underplated layer may represent a combination of different intrusive rock types (e.g., gabbro, anorthosite) developed during magma differentiation processes, or contamination of the mafic magma by surrounding crustal material, or intrusions of sills. • High-resolution crustal and uppermost mantle structure of the Midcontinent Rift in North America is imaged. • High Vp and density anomalies in the upper crust are consistent with high Bouguer anomalies within the rift. • Extensive and anomalous Vs and Vp structures indicate magmatic underplating within the lower crust. • Underplated materials may have variable compositions, such as gabbro and anorthosite. [ABSTRACT FROM AUTHOR]

Solvent-free oxidation of benzyl alcohol on bimetallic Pt-Bi catalysts supported on activated carbon (AC), carbon black, carbon nanotube, and N-doped carbon (NC) was studied. While the dispersions of both metals significantly increased on all the bimetallic catalysts, the composition and distribution of the metal species were strongly influenced by different supports. The formation of PtBi alloy was favored on most supports except AC, where aggregation of Bi was observed. Moreover, the oxidation activity was found to closely link to the surface Bi:Pt ratios. Extensive optimizations on PtBi/NC catalyst in batch and flow reactors yielded impressive benzaldehyde yields of 86 % and 70 %, respectively, under mild conditions, which are comparable or even superior to the performances of most state-of-the-art catalysts. Notably, a 96-hour continuous test in a trickle-bed reactor demonstrated stable operation without catalyst deactivation, demonstrating the promising industrial potential. [Display omitted] • Bimetallic Pt-Bi catalysts on various carbon supports are prepared. • Support choice affects metal species composition and distribution on catalysts. • PtBi alloy favored on most supports except AC, where Bi aggregation occurs. • Performance in batch and flow reactors is examined in benzyl alcohol oxidation. • Optimizations on PtBi/NC yield high benzaldehyde yields, stable operation. [ABSTRACT FROM AUTHOR]

Abstract: Activated carbon-supported La-promoted Co catalysts with different La dopings (15Co–xLa/AC) were prepared by the co-impregnation method and investigated by means of CO hydrogenation, XRD, TPR-MS, CO adsorption and TPSR-MS techniques. The results showed that mixed linear α-alcohols (C1–C18) can be directly synthesized from syngas over the La-doped 15Co/AC catalysts under mild conditions and that the selectivity towards alcohols was improved by doping La into the 15Co/AC catalysts. It was found that the reducibility of the 15Co–xLa/AC catalyst decreased and the Co dispersion improved due to the strong interaction between Co and La2O3 species. La2O3 can promote the formation of cobalt carbides (Co2C), which are postulated to play an important role in the syntheses of the mixed linear α-alcohols. On the other hand, high Co dispersion and an appropriate ratio of Co2+/Co0 can enhance the activity of CO hydrogenation. [Copyright &y& Elsevier]

[Display omitted] • Supported ReCu catalysts were synthesized for DMO hydrogenation to ethanol. • The Re 2 Cu 5 /ZrO 2 catalyst exhibited the best catalytic performance. • The molar ratio of Cu0 and Cu+, reduction degree and copper particle size play the pivotal role. • Good stability of Re 2 Cu 5 /ZrO 2 catalyst. Addition of oxophilc rhenium to decorate small copper nanoparticles has been validated to be an efficient method to prepare a low-copper catalyst for the direct synthesis of ethanol via dimethyl oxalate (DMO) hydrogenation process, and herein we investigated the impact of supports on the catalytic performance of ReCu catalysts. A series of materials including activated carbon (AC), Al 2 O 3 , SiO 2 , TiO 2 and ZrO 2 were utilized as the support and as prepared Re 2 Cu 5 catalysts were evaluated. The results exhibited that the Re 2 Cu 5 /ZrO 2 catalyst possesses the highest DMO hydrogenation activity and ethanol yield (∼93%), which may be due to its lowest Cu0/Cu+ ratio (0.13), smallest Cu particle size (∼0.84 nm) a relative high reduction degree (59%). The CO adsorption behavior characterized by in si tu IR spectroscopy showed that a strong metal-support interaction creates an electron deficient environment of Cu nanoparticle, resulting in a lower Cu0/Cu+ ratio that enhances the activation of C O bond in the DMO molecular. [ABSTRACT FROM AUTHOR]

The hybridization of abundant transition metals with facile nitrogen‐doped carbons is an effective strategy to fabricate advanced functional materials for targeted applications. Herein, we demonstrate a novel and straightforward synthetic approach of preparing a series of different transition metal‐modified nitrogen‐doped carbons (M/NC, M=Fe, Co, Ni) through the addition of corresponding metal sulfates during the polymerization of aniline, followed by high‐temperature (873–1273 K) pyrolysis treatment. While Fe/NC features predominantly single Fe atoms, nanoparticles of mixed metal oxides and or carbonates are formed on Co/NC and Ni/NC. When employed in the selective oxidation of ethyl benzene by using tert‐butyl hydroperoxide both as the solvent and the oxidant, these materials showed promoted catalytic response with the order of Fe>Co>Ni as compared with the metal‐free analogue. The performance can be further tuned by controlling the pyrolysis temperature, and the best performance can be achieved over Fe/NC‐1273 (0.153 wt.% Fe), affording an unprecedented acetophenone yield of 98 % and excellent cycling performance. [ABSTRACT FROM AUTHOR]

Although numerous efforts have been made in direct syngas conversion to higher alcohols via Fischer–Tropsch synthesis, the higher alcohols distribution remains a challenge. Here, we introduce alkaline earth metal oxide as promoter into activated carbon supported cobalt catalyst to tune distribution of higher alcohols. With the addition of Mg, the distribution of C2-5 alcohols increase from 41.2 to 75.8% accompanying with distribution of C6-18 alcohols decrease from 52.8 to 14.0%. Ba-promoted Co based catalyst (CoBa/AC) presents similar alcohols distribution to un-promoted catalyst, while the alcohol selectivity over CoBa/AC is higher than Co/AC. For promoted catalysts, the distribution of C6-18 alcohols increased in the order of Mg < Ca < Sr < Ba. The characterization results exhibit that the promoter addition facilitates the cobalt carbide formation, which leads to enhancement of selectivity to higher alcohols. The available active cobalt sites of promoted Co based catalysts increase in the same above order of Mg < Ca < Sr < Ba. [ABSTRACT FROM AUTHOR]

Compared with traditional adjoint-based migration, least-squares migration (LSM) can reduce finite-frequency effects, remove acquisition footprints and improve spatial resolution by solving a linear inverse problem for subsurface reflectivity. One important requirement for the success of LSM is having an accurate migration velocity model. Because of low signal-to-noise ratio (SNR), inaccurate traveltime picking, lack of low-frequency signals and limited acquisition aperture, it is still challenging to build an accurate velocity model using ray-based tomography or full waveform inversion. LSM with large velocity errors results in erroneous reflector locations, strong swing artifact and even non-convergence. To mitigate these issues, we develop a novel least-squares imaging framework in the subsurface half-opening angle domain. Instead of using high-wavenumber velocity perturbations as the reflectivity model as in traditional LSM, we parameterize the wave equation with an angle-dependent reflectivity, and derive the corresponding linearized forward modeling and adjoint migration operators. Because Gaussian Beam migration naturally incorporates propagation directions in wavefield extrapolation, we compute the Green's function using the Gaussian beam summation method. To improve the common-image gather (CIG) quality for low-fold and low-SNR data, a shaping regularization over the half-opening angles is introduced in the conjugate gradient scheme to iteratively update the angle-dependent reflectivity model. A flattening-enhanced summation is used to compute the stacked images by accounting for the depth moveout of CIGs caused by velocity errors, and produces constructive stacking results. Numerical experiments for benchmark models and a land survey demonstrate that the proposed method can improve LSM convergence and produce high-quality angle-dependent and stacked images even with inaccurate migration velocity models. [ABSTRACT FROM AUTHOR]

Promotional effects of oxygen vacancies of spinel catalysts in CO 2 hydrogenation are reported in early works, but the mechanistic origins remain elusive. Here, CoAl 2 O 4 spinels with varying numbers of oxygen vacancies are deliberately designed by a sol-gel method and different post-treatments. By combining catalytic testing, advanced electron microscopic and spectroscopic characterizations, and computational studies, the unusual oxygen vacancy-dependent catalytic behaviors are rationalized. Our work reveals that i) perfect spinel crystals possessing least oxygen vacancies can effectively constrain the Co2+ species at working conditions that are less active but selective to CO; and ii) vacancy-rich spinels promote both H 2 and CO 2 activations and COOH* formation, explaining the higher hydrogenation activity, but overwhelming vacancies cause Co2+ reduction and promote direct CO 2 * dissociation to CO* and deep hydrogenation to CH 4. These molecular-level understandings reinforce the idea of proper design of oxygen vacancies to achieve activity-selectivity balance. [Display omitted] • CoAl 2 O 4 spinels with different numbers of oxygen vacancies were designed. • CoAl 2 O 4 spinels presented divergent CO 2 hydrogenation performances. • Complex interplay among oxygen vacancies, catalyst structure and CO 2 hydrogenation performances were revealed. • Mechanistic origins of the multifaceted roles of oxygen vacancies were unveiled by DRIFT and DFT. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient hcp-Co active sites on CoZr/AC for FTS were constructed. • The reaction performance was affected by the activation strategy. • Hcp-Co exhibited higher CO hydrogenation intrinsic activity than fcc-Co. • Higher activity was observed for CoZr/AC-RSCR with higher hcp-Co content. • Extremely high fuels productivity of 194.6 g/h·kg-catalyst was acquired. A highly efficient activated carbon supported cobalt based catalyst for Fischer-Tropsch synthesis was constructed. The catalyst was prepared by incipient wetness co-impregnation. The obtained catalyst was activated by multistep activation processes, which was composed of reduction of calcined sample in H 2 , syngas treatment, carburization in CO, and re-reduction in H 2 successively. The multistep activation processes derived catalyst (CoZr/AC-RSCR) demonstrated far higher CO conversion and lower CH 4 selectivity than those of conventional H 2 reduction derived catalyst (CoZr/AC-R). The excellent performance of CoZr/AC-RSCR catalyst resulted from its higher amount of exposed active sites and the dominant hexagonal closed-packed (hcp) metallic cobalt phases. Furthermore, the catalytic performance could be further improved by tuning the content of hcp metallic cobalt phase stacking using the proper and effective treatment conditions of the multistep activation method. Finally, extremely high productivity of the mixture of alcohols and hydrocarbons with carbon number larger than 5 (194.6 g/h·kg-cat.) was acquired over CoZr/AC catalyst. [ABSTRACT FROM AUTHOR]

Traditional elastic reverse-time migration (RTM) involves P-/S-wave separation for the source and receiver wavefields, followed by applying the zero-lag cross-correlation imaging condition to produce PP and PS images. In anisotropic media, P-/S-wave decomposition requires a higher memory and computational cost than that in isotropic media. In addition, finite acquisition apertures and band-limited source functions result in unsatisfactory resolutions and amplitudes. To mitigate these problems, we present an elastic least-squares imaging method for tilted transversely isotropic media and apply it to land multicomponent and marine pressure data. Unlike traditional RTM, we use the relative perturbations to the product of density and squared axial (compressional/shear) velocities as reflectivity models ( Δ ln C 33 and Δ ln C 55 ), and estimate them by solving a linear inverse problem. Numerical experiments illustrate that subsurface reflectors can be well resolved in adjoint images for land multicomponent data, because of the presence of both P- and S-waves in seismograms. Least-squares migration helps to further improve spatial resolution and image amplitudes. Since there are no direct S-waves in marine streamer data, adjoint RTM images of Δ ln C 55 are mainly resolved with the converted S-waves and are not as good as those in Δ ln C 33 images. By approximating the Hessian inverse, least-squares migration allows us to take advantage of the weak converted P–S–P-waves and improve the Δ ln C 55 image quality. Numerical experiments for synthetic and field data demonstrate the feasibility and advantage of the proposed least-squares TTI RTM compared with wave-mode separation-based elastic RTM. In field data experiments, we observe that since there are no strong P–S–P converted waves in streamer pressure records from the marine survey, the reflectors in Δ ln C 55 image might be mainly imaged from P-waves due to the amplitude versus offset (AVO) effects. [ABSTRACT FROM AUTHOR]

• Environmentally benign Cu-based catalysts are desirable for DMO hydrogenation. • Cu-Zn bimetallic catalysts with intimate metal contact are designed and tested. • Activity descriptor is reexamined and stability descriptor is unraveled. • High activity and excellent stability are achieved in the ethylene glycol production. The development of robust catalysts for selective hydrogenation of dimethyl oxalate (DMO) is key for the expansion of ethylene glycol (EG) production from C1 and renewable feedstocks. Copper-based catalysts promoted with Cr are industrially used, but it is desirable to develop more environmentally-benign alternatives. Silica-supported copper-zinc bimetallic catalysts featuring intimate metal contact are designed and used to establish the structure-performance relationships through combining in-depth characterizations with steady-state catalytic testing. Our study highlights: i) that the surface Cu0/Cu+ ratio is a reliable catalytic descriptor that determines the activity and selectivity, and ii) the importance of copper-zinc interface in stabilizing copper nanoparticles both under reduction and hydrogenation conditions. Controlled zinc doping allows fine tuning of these properties for the targeted reaction. Excellent performance has been achieved on the best-performing catalyst with >99.6% DMO conversion, >96.0% EG selectivity, and unprecedented stability of 800 h without catalyst deactivation, which represents a significant advance in the selective hydrogenations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Activity and C 5+ selectivity of Co/AC catalyst are increased by Cr promotion. • Addition of Cr enhances H 2 adsorption over CoxCr/AC catalysts. • Relative H-rich and C-lean surface chemical environment facilitates paraffins formation and inhibits Co 2 C formation. • Cr oxide accumulates preferentially on the surface of the AC support. • Cr oxide migrates gradually onto the surface of Co nanoparticles at high loadings. Abstract Synthesis of clean transportation fuels from syngas (CO + H 2) derived from coal, natural gas, and renewable biomass is an efficient method for reducing dependence on oil reservoirs, for which developing effective catalysts is significant. Co-based catalysts supported by carbon materials possess advantages such as longer lifetimes and easy handling of wasted catalysts, but increasing their activity and selectivity remains a challenge. Here we report using Cr as a promoter to enhance the CO hydrogenation process over activated carbon (AC)-supported Co-based catalysts, namely, CoxCr/AC catalysts. An almost twofold increase in activity (from 28.9% to 47.0%), accompanied by decreased CH 4 , olefin, and alcohol selectivity, was achieved by adding Cr, resulting in a significant increase in the yield of transportation fuel products. The results of chemisorption indicate that Cr facilitates H 2 adsorption and suppresses the formation of cobalt carbide (Co 2 C), forming a relative H-rich and C-lean surface chemical environment, so that the CO hydrogenation process and C–C coupling step are enhanced. Structural characterizations show that Cr exists in the form of Cr 2 O 3 and aggregates on the surfaces of the catalysts in a highly dispersed manner at relative low loadings (<2 wt%), and that Co nanoparticles are partly covered by Cr at high loadings. We suggest that the interaction between Cr3+ and adjacent metallic Co may play a pivotal role in the elevation of CO hydrogenation activity and C 5+ selectivity. [ABSTRACT FROM AUTHOR]

Designing efficient non-precious metal catalysts for CO 2 hydrogenation is a significant challenge. Cobalt-based catalysts often failed to catalyze the reverse water-gas shift (RWGS) reaction with high CO selectivity and stability. Herein, nitrogen-doped carbon (N-C) immobilized single-atom Co-N 4 catalyst with 5% Co loading were prepared by anchoring strategy through regulating the cobalt species coordination structure. The stable single-atom catalyst achieves almost 100% CO selectivity and a high CO 2 conversion of 52.4% at 500 °C during CO 2 hydrogenation, while the 20% Co-N-C nanoparticle catalyst favored CH 4 formation. The experiments and density functional theory (DFT) calculations revealed that atomically dispersed Co-N 4 site followed the hydrogen-assisted pathway in which the intermediate COOH* was desorbed and dissociated into CO, whereas the Co nanoparticle catalysts mainly followed the direct dissociation. This study provided a new strategy for designing Co-based RWGS catalysts with excellent performance. [Display omitted] • The single-atom Co-N 4 catalyst with 5% Co loading is successfully synthesized through the anchoring strategy. • The stable single-atom catalyst achieves almost 100% CO selectivity and high conversion of 52.4% at 500 °C during CO 2 hydrogenation. • This work provided a new strategy for designing Co-based RWGS catalysts with excellent performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mo-doped Cu/SiO 2 catalysts were synthesized for DMO hydrogenation to ethanol. • The Mo 3 Cu 20 /SiO 2 sample exhibited the best ethanol yield (up to 94%). • The Lewis acidity and a balanced Cu0/Cu+ resulted from the interaction between MoO x and Cu NPs play the pivotal role. • Excellent stability of Mo 3 Cu 20 /SiO 2 catalyst. The environmentally-benign hydrogenation of dimethyl oxalate to produce ethanol has attracted considerable attention recently, and the yield of which remains a challenge for the commonly used Cu-based catalysts. Herein we reported a molybdenum-doped Cu catalyst synthesized by impregnating Mo on the Cu/SiO 2 composite prepared by an ammonia evaporation hydrothermal method, and the Mo 3 Cu 20 /SiO 2 sample exhibited the best compromise between activity and ethanol selectivity, acting as a robust catalyst (460 h time on stream) with a high ethanol yield (∼94 %). It is demonstrated that Mo doping elevates the amount of surface Cu+ species through the strong interaction between MoO x and Cu species, and the balanced Cu0/Cu+ ratio and enhanced surface acidity resulted by Mo addition afford the high ethanol selectivity through facilitating the dehydroxylation of ethylene glycol, whose activation energy over Mo 3 Cu 20 /SiO 2 is 79.9 kJ/mol, lower than that of Cu 20 /SiO 2 catalyst (108.1 kJ/mol). [ABSTRACT FROM AUTHOR]

This author wishes to remove his name from the list of authors. Correction to: Surveys in Geophysics (2021) 42:1305-1346 https://doi.org/10.1007/s10712-021-0... In the article published, on 15 November 2021, in Surveys in Geophysics 42, 1305-1346 (2021), the name of the seventh author, Chaoshun Hu, was regrettably included in error. [Extracted from the article]

The heterogenization of homogeneous catalysts is of critical importance for both fundamental research and practical applications. The key obstacle to industrial applications of heterogenized homogeneous catalysts is the long-term stability of the immobilized molecular complexes. We unambiguously demonstrate in this report that the vinyl-functionalized PPh 3 polymers supported single Rh sites (Rh/POL–PPh 3 ) catalyst provided not only excellent catalytic activity but also ultrahigh stability for fixed-bed olefins hydroformylation, which is one of the most important industrial homogeneous catalytic processes for the synthesis of aldehydes and alcohols. HAADF-STEM and EXAFS results indicated that the Rh atoms were present in single Rh sites which were strongly coordinated with the exposed phosphorous atoms of the POL–PPh 3 support. The Rh/POL-PPh 3 catalyst provided high activity and selectivity because it maintained the catalytic functionalities similar to the homogeneous HRh(CO)(PPh 3 ) 3 complex, as demonstrated both by 31 P MAS NMR and in situ FT-IR experiments. Thus a reaction mechanism, similar to that over the homogeneous HRh(CO)(PPh 3 ) 3 complex, was proposed for olefin hydroformylation over the novel Rh/POL–PPh 3 catalyst. [ABSTRACT FROM AUTHOR]

A Rh/SiO 2 catalyst with excellent activity and stability for ethylene hydroformylation was developed by modifying with tethered diphenylphosphinopropyl and doped with an Al promoter. The catalyst was characterized by means of N 2 adsorption/desorption isotherms, transmission electron microscope, NH 3 temperature programmed desorption, Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance. Experimental results showed that the existence of the Al promoter inhibited the growth of Rh particles, increased the number of exposed Rh atoms, changed the acidity of the catalyst surface, promoted in situ formation of active species that were similar to their corresponding homogeneous counterparts, and enhanced electron density of the P atom in the phosphine ligand. [ABSTRACT FROM AUTHOR]

Abstract: A tethered ligand-modified Rh/SiO2 catalyst was developed for hydroformylation with high stability. The catalyst was prepared by fastening both organic ligand and metal directly on the surface of support to avoid leaching, while at the same time the active species were formed in situ by coordination of the flexible ligand to the metal on the surface of SiO2. The immobilization of ligand on SiO2 and the interaction between ligand and metal were investigated by means of TG, solid-state NMR and FTIR. Hydroformylation of ethylene was selected as a probe reaction to evaluate the immobilization and coordination of ligand to the nano-metal particles. High activity and excellent stability were observed during a 1000-h run. [Copyright &y& Elsevier]