Ethanol dehydrogenation presents a promising pathway toward the production of acetaldehyde, a valuable building block in chemicals production. Under nonoxidative conditions, the reaction is facilitated by supported Cu nano particles, which afford reasonable activity and high selectivity. The stability issues associated with Cu nanoparticle sintering can be addressed by the addition of small amounts of Ni, which further boost reactivity while retaining selectivity. Despite the promise of NiCu single-atom alloys for nonoxidative ethanol dehydrogenation, little is known about the role of each component and the pathway of this mechanistically complex process. Herein, kinetic investigations from reactor tests identify C-H bond scission as the rate-limiting step, while 1-hydroxyethyl is detected as the intermediate via IR spectroscopy. Temperature-programmed desorption studies are employed to examine the effect of Ni coverage and to demonstrate that Ni atoms activate ethanol selectively at lower temperatures, resulting in higher acetaldehyde yield than pure Cu. Temperature-programmed desorption experiments also reveal the spillover of intermediates from the Ni atom to neighboring Cu sites as a relevant step in the reaction pathway. Density functional theory calculations are used to investigate the reaction energetics and to confirm that C-H bond scission is the initial reaction step, while a clear effect of H2 partial pressure on the reaction pathway is realized. Further, counter to the expected behavior that all reaction steps take place on the Ni atoms, our degree of rate control analysis reveals that a mechanism involving spillover of the 1-hydroxyethyl intermediate from the Ni atom to the Cu surface, where it will dehydrogenate further, is more likely. Our combined kinetic, spectroscopic, and theoretical approach sheds light on this complex reaction mechanism and represents a promising method for the understanding and designing of highly active, selective, and stable single-atom alloys for other multistep catalytic processes.

In continuation of our two-step process development for the conversion of ethane to aromatics, this work focuses on catalyst performance improvement for ethylene aromatization. The approach is to apply steaming dealumination method to tailor ZSM-5 acidity to optimize its catalytic performance. Our results indicate that applying steaming treatment for the base Ga-ZSM-5 catalyst at specified conditions could reduce the total acid amount from 0.46 to 0.15-0.25 mmol/g, with 46-67% acidity loss, accompanied with the decrease of the acid strength for the strong acid sites. As a result, the catalyst prepared in this way exhibited a step-change performance enhancement in terms of cycle lifetime, target product yield/capacity, byproduct, coke formation and so on. Through examining the reaction mechanism and acid strength requirements for individual steps involved in ethylene aromatization, we conclude that steps that require strong acid strength - such as cracking and aromatics alkylation (both leading to catalyst deactivation) are effectively suppressed due to the lower acid amount/ strength obtained after steaming treatment. The findings and this zeolite acidity tailoring technique will provide insights and solutions for zeolite-based acidic catalyst design.

The development of transition metal carbides, for example, Pd carbide, Mo carbide, Co carbide, and Fe carbide for catalytic applications has attracted significant attention. Pt carbide has also been actively pursued, however, no catalytic examinations of Pt carbide have been performed, likely due to its extreme synthesis conditions. Here, we report a facile synthesis of Pt carbide nanomaterials under mild conditions, for the first time, through ethane treatment of confined Pt nanoclusters under mild temperatures and ambient pressure. Such Pt carbide nanomaterials exhibit remarkable activity in catalytic hydrocarbon conversion, including ethane aromatization and acetylene hydrogenation, and are superior over supported Pt nanoparticles. Our work further reveals that Pt nanoclusters are favored in terms of forming Pt carbide when compared to isolated single Pt atoms and large Pt nanoparticles. This work provides a new approach to prepare metal carbide based catalytic materials through nanoclusters under mild conditions.

Direct conversion of light alkanes, specifically ethane to aromatics, has been an important research goal for both academia and industry over the past several decades. Despite a significant research investment, there have been no major technical breakthroughs to date, due in large part to the inability to develop catalysts with satisfactory performance. This article proposes a two-step process concept for aromatics production from ethane that has the potential to address this impasse. Our process involves performing the dehydrogenation of ethane in a first step, followed by ethylene aromatization in a separate reactor. We begin by reviewing the major fundamental and technical hurdles associated with efforts to develop one-step processes and use this to show how our two-step process can overcome limitations in the reaction pathway, thermodynamics, and catalyst performance encountered in the one-step approach. We then describe catalyst validation, reactor design, and process economics to illustrate the value of our concept.

In this work, one-step conversion of methane to methanol using molecular oxygen as the oxidant in the presence of CO in aqueous solutions on copper or palladium promoted Ir-ZSM-5 catalyst is first reported. The addition of a second metal to Ir-ZSM-5 promotes the catalyst activity, while product selectivity can be tuned either to methanol on IrCu-ZSM-5 or to formic acid exclusively on IrPd-ZSM-5. Most effective is the combination of the three metal species together. Approximately 1200 mu mol/g(cat) methanol, or similar to 23.4 mol of methanol per mol of Ir, are formed on the IrCuPd trimetallic system (methanol selectivity similar to 80 %) at 150 degrees C in 1 h. Our results also demonstrate that atomically dispersed Ir(I)(CO)(2) species formed in the presence of CO can activate the C-H bond of methane to methyl species at temperatures below 150 degrees C. The good stability in cyclic operation is an additional attribute, rendering this type of catalyst a "front-runner" in future catalyst development for direct methane-to-liquid oxygenates.

•Bimetal nickel/gallium co-functionalized HZSM-5 catalyst was developed for ethane aromatization to enhance the activity and stability.•The metal function of the catalyst significantly affect the early-stage induction period.•The formation of Ni3Ga alloy and its synergy with the exchanged Gaδ+ could be responsible for optimal BTX formation.•The long-term deactivation kinetics were evaluated.

The reactivity of HZSM-5 catalysts for ethylene oligomerization is highly dependent upon their framework Alf proximity.

In situ and ex situ X-ray photoelectron spectroscopy and electron-microscopy reveal that the stability of nanoporous NiCu alloy catalysts for non-oxidative ethanol dehydrogenation improves by generating kinetically trapped Ni2+ subsurface states.

Ceria has been widely used as support in electrocatalysis for its high degree of oxygen storage, fast oxygen mobility, and reduction and oxidation properties at mild conditions. However, it is unclear what are the underlying principles and the nature of surface involved. By controlling the growth of various morphologies of ceria nanoparticles, it is demonstrated that the cubic-form of ceria, predominantly covered with higher energy polar surface (100), as support for Pd gives much higher activity in the electrocatalytic oxidation of formic acid than ceria of other morphologies (rods and spheres) with low-indexed facets ((110) and (111)). High-resolution transmission electron spectroscopy confirms the alternating layer-to-layer of cations and anions in (100) surface, and the electrostatic repulsion of oxygen anions within the same layers gives intrinsically higher oxygen vacancies on this redox active surface in order to reduce surface polarity. Density functional theory calculations suggest that the properties of fast oxygen mobility to reoxidize the CO-poisoned Pd may arise from the overdosed oxygens on these ceria surface layers during electro-oxidation hence sustaining higher activity.

In an effort to obtain the maximum atom efficiency, research on heterogeneous single-atom catalysts has intensified recently. Anchoring organometallic homogeneous catalysts to surfaces creates issues with retaining mononuclearity and activity, while the several techniques developed to prepare atomically dispersed precious metals on oxide supports are usually complex. Here we report a facile one-pot synthesis of inorganometallic mononuclear gold complexes formed in alkaline solutions as robust and versatile single-atom gold catalysts. The complexes remain intact on impregnation onto supports or after drying in air to give a crystalline powder. They can be used to interrogate the nuclearity of the catalytically active gold site for reactions known to be catalysed by oxidized gold species. We show that the [Au1–Ox]– cluster directs the heterogeneous coupling of two methanol molecules to methyl formate and hydrogen with a 100% selectivity below 180 °C. The reaction is industrially important as well as the key step in methanol steam reforming on gold catalysts. Generating stable single-atom catalysts is far from straightforward and can involve complicated preparation procedures. Now, mononuclear gold oxo-clusters formed in alkaline solutions through a facile one-pot synthesis are shown to catalyse the heterogeneous methanol self-coupling reaction to methyl formate and hydrogen. The intrinsic activity is the same for both supported and unsupported gold catalysts.

Catalytic conversion of ethane to aromatics (BTX) over metal/HZSM-5 catalysts involves significant catalyst deactivation due to coking. Consequently, true acidity/performance relationships are escaped if the intrinsic catalyst acidity was correlated to the "steady-state" performance. Here, the effect of acidity on the early-stage performance and time-dependent deactivation kinetics has been investigated. The early-stage ethane conversion and BTX selectivity both increased with decreasing Si/Al-2 ratios. Specifically, the space-time yields of BTX increase linearly with increasing Bronsted acidity, indicating Bronsted acids as the main active sites for BTX. Further evidence can be found from the transient experiment (C2H6/Ar <-> C2H6/NH3) and C2H4-TPSR. A promotion effect of the Zn(II) sites (mainly responsible for ethane dehydrogenation) on BTX formation was also observed. With time-on-stream, the catalytic performance attenuated due to coking, which can be modeled as "r(t) = r(0)/(1 + kt(alpha))" kinetically, and the parameters (for aromatics) k decreased and alpha increased with decreasing acidity.

The selective hydrogenation of alkynes to alkenes is an important industrial process. However, achieving high selectivity and reducing the usage of precious platinum group metals are still challenging for the conventional hydrogenation catalysts. With atomically dispersed active metal atoms on the surface of a host metal, single-atom alloys (SAAs) have shown excellent hydrogenation selectivity and activity, but their hydrogenation mechanism is not fully understood. This work reports on the selective hydrogenation of 1-hexyne to 1-hexene on PdAu SAA catalysts. Au is a highly selective hydrogenation catalyst, but it is not active at low temperatures. Through measurements of reaction kinetics and in operando spectroscopy studies, we follow the much more facile activation of PdAu SAA catalysts and demonstrate the different hydrogenation chemistry of single Pd atoms and Pd nanoparticles (NPs). We further investigate the role of Pd atoms and the mechanism behind the improved hydrogenation selectivity through surface science and density functional theory. These studies indicate that the difference in reactivity stems from the relative energy barrier heights for over-hydrogenating the terminal C atom. The complementary catalysis-surface science-theory investigation described here is a powerful and general approach for understanding and controlling NP performance. The selective hydrogenation on PdAu SAAs is demonstrated and understood fundamentally, which serves as a guide for future designs of this type of catalyst.

Gold is examined here as an alternative to copper for the selective dehydrogenation of ethanol to acetaldehyde and hydrogen. Despite its high selectivity, gold is only active at temperatures higher than 250 °C for this reaction. We demonstrate that addition of a small amount of Ni on either supported or unsupported Au surfaces induces resistance to sintering, along with a beneficial effect on the catalytic activity. NiAu alloys prepared here with Ni as the minority component to the limit of atomic dispersion in the gold surfaces, catalyze the reaction beginning below 150 °C. A significant decrease of the apparent activation energy from 96 ± 3 kJ/mol for the monometallic Au to 59 ± 5 kJ/mol for the alloy was found. The Ni dispersion and concentration as a function of gas environment was followed by in situ DRIFTS and by XPS. The stability of the catalyst morphology was investigated through post-reaction microscopy imaging and long-term stability tests under reaction conditions. As shown via dynamic reaction experiments, acetaldehyde and H2 were selectively produced up to 280 °C. A small drop of selectivity at higher temperatures is attributed to the formation of Ni clusters, as proven by CO-DRIFTS on the used sample. Comparison with samples of higher Ni loading, where Ni clusters are formed, clearly shows that they catalyze the undesired full decomposition of ethanol to CO, CH4, and H2.

The non-oxidative dehydrogenation of ethanol to acetaldehyde has long been considered as an important method to produce acetaldehyde and clean hydrogen gas. Although monometallic Cu nanoparticles have high activity in the non-oxidative dehydrogenation of ethanol, they quickly deactivate due to sintering of Cu. Herein, we show that adding a small amount of Ni (Ni-0.01 Cu - Ni-0.00 Cu) into Cu to form highly dilute NiCu alloys dramatically increases the catalytic activity and increases their long-term stability. The kinetic studies show that the apparent activation energy decreases from similar to 70 kJ/mol over Cu to similar to 45 kJ/mol over the dilute NiCu alloys. The improved performance is observed both for nanoparticles and nanoporous NiCu alloys. The improvement in the long-term stability of the catalysts is attributed to the stabilization of Cu against sintering. Our characterization data show that Ni is atomically dispersed in Cu. The comparison of the catalytic performance of highly dilute alloy nanoparticles with banoporous materials is useful to guide the design of novel mesoporous catalyst architectures for selective dehydrogenation reactions. (C) 2017 Elsevier B.V. All rights reserved.

CO hydrogenation to higher alcohols (C2+OH) provides a promising route to convert coal, natural gas, shale gas, and biomass feedstocks into value-added chemicals and transportation fuels. However, the development of nonprecious metal catalysts with satisfactory activity and well-defined selectivity toward C2+OH remains challenging and impedes the commercialization of this process. Here, we show that the synergistic geometric and electronic interactions dictate the activity of Cu-0-chi-Fe5C2 binary catalysts for selective CO hydrogenation to C2+OH, outperforming silica-supported precious Rh-based catalysts, by using a combination of experimental evidence from bulk, surface-sensitive, and imaging techniques collected on real and high-performance Cu-Fe binary catalytic systems coupled with density functional theory calculations. The closer is the d-band center to the Fermi level of Cu-0-chi-Fe5C2(510) surface than those of chi-Fe5C2(510) and Rh(111) surface, and the electron-rich interface of Cu-0-chi-Fe5C2(510) due to the delocalized electron transfer from Cu-0 atoms, facilitates CO activation and CO insertion into alkyl species to C-2-oxygenates at the interface of Cu-0-chi-Fe5C2(510) and thus enhances C2H5OH selectivity. Starting from the CHCO intermediate, the proposed reaction pathway for CO hydrogenation to C2H5OH on Cu-0-chi-Fe5C2(510) is CHCO + (H) -> CH2CO + (H) -> CH3CO + (H) -> CH3CHO + (H) -> CH3CH2O + (H) -> C2H5OH. This study may guide the rational design of high-performance binary catalysts made from earth-abundant metals with synergistic interactions for tuning selectivity.

An efficient and direct method of catalytic conversion of methane to liquid methanol and other oxygenates would be of considerable practical value. However, it remains an unsolved problem in catalysis, as typically it involves expensive or corrosive oxidants or reaction media that are not amenable to commercialization. Although methane can be directly converted to methanol using molecular oxygen under mild conditions in the gas phase, the process is either stoichiometric (and therefore requires a water extraction step) or is too slow and low-yielding to be practical. Methane could, in principle, also be transformed through direct oxidative carbonylation to acetic acid, which is commercially obtained through methane steam reforming, methanol synthesis, and subsequent methanol carbonylation on homogeneous catalysts. However, an effective catalyst for the direct carbonylation of methane to acetic acid, which might enable the economical small-scale utilization of natural gas that is currently flared or stranded, has not yet been reported. Here we show that mononuclear rhodium species, anchored on a zeolite or titanium dioxide support suspended in aqueous solution, catalyse the direct conversion of methane to methanol and acetic acid, using oxygen and carbon monoxide under mild conditions. We find that the two products form through independent pathways, which allows us to tune the conversion: three-hour-long batch-reactor tests conducted at 150 degrees Celsius, using either the zeolite-supported or the titanium-dioxide-supported catalyst, yield around 22,000 micromoles of acetic acid per gram of catalyst, or around 230 micromoles of methanol per gram of catalyst, respectively, with selectivities of 60-100 per cent. We anticipate that these unusually high activities, despite still being too low for commercial application, may guide the development of optimized catalysts and practical processes for the direct conversion of methane to methanol, acetic acid and other useful chemicals.