Ethylene Selectivity Research Articles

CH4 Carbonylation to Acetic Acid Using H2O as an Oxidant on a Rh-Functionalized UiO-67 Combined with Oriented External Electric Fields: Selectivity and Mechanistic Insights from DFT Calculations.

Acetic acid (CH3COOH), as an industrially important petrochemical product, is predominantly produced via multistep energy-intensive processes. The development of a rhodium single-site heterogeneous catalyst has received considerable attention due to its potential to transform CH4 into CH3COOH in a single step. Herein, the reaction mechanism for the generation of CH3COOH from CH4, CO, and H2O catalyzed by Rh-functionalized metal-organic framework (MOF) UiO-67 and the selectivity of products CH3COOH, formic acid (HCOOH), methanol (CH3OH), and acetaldehyde (CH3CHO) under the oriented external electric fields (OEEFs) were systematically explored by density functional theory (DFT) calculations. The results reveal that the insertion of CO into Rh-CH3 is the rate-determining step with a free energy barrier of 21.0 kcal/mol in CH4 carbonylation to CH3COOH. Upon applying an OEEF of Fx = +0.0050 au along the C-C bond, the rate-determining step shifts toward H2O decomposition with the barrier of 19.6 kcal/mol, significantly improving the selectivity for CH3COOH production, compared to the major competitive HCOOH route. The Brønsted-Evans-Polanyi (BEP) relationships between key transition states, field strength, and NPA charge transfer were established. This study may guide the rational design of atomically dispersed MOF catalysts for the selective coconversion of CH4 and CO to CH3COOH using H2O as the oxidant under the OEEF.

Interface engineering to construct heterostructured MoO3/SmMn2O5 for chemical looping oxidative dehydrogenation of ethane

Electronic structure and lattice oxygen in metal oxides play important roles in the chemical looping oxidative dehydrogenation of ethane. Herein, an interface strategy is proposed to tailor electronic structure and activate lattice oxygen of mullite SmMn2O5 via the interface fabrication with MoO3 for enhancing the reactivity of the sample. The optimized 2MoO3/SmMn2O5 oxygen carrier exhibited 50 % ethane conversion and 83.9 % ethylene selectivity higher than that of pure SmMn2O5 and pure MoO3. Density functional theory simulations and characterization results revealed that the interface of MoO3/SmMn2O5 regulated the d-band center, which tailored the adsorption of ethane. Besides, the interface of MoO3/SmMn2O5 also caused the charge transfer from Mn atoms in SmMn2O5 to O atoms in MoO3 and SmMn2O5, leading to a reduction of the Mn-O bond strength and an enhancement in the activity of the lattice oxygen and Oads. This study provides useful insights to regulate electronic structure and activate lattice oxygen of oxygen carrier through interfacial engineering for the practical application of ethane chemical looping oxidative dehydrogenation.

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism.

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen-containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming-induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual-cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol-to-hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using "mobility-dependent" solid-state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual-cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene-based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming-induced changes in the organic reaction mechanisms with inorganic material aspects.

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen‐containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming‐induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual‐cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol‐to‐hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using “mobility‐dependent” solid‐state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual‐cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene‐based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming‐induced changes in the organic reaction mechanisms with inorganic material aspects.

On the Role of Anions in Solid Catalysts with Ionic Liquid Layer (SCILL) for the Selective Hydrogenation of Highly Concentrated Acetylene Streams.

Electric plasma assisted pyrolysis of methane represents a highly promising greener alternative to produce ethylene from biogas and renewable energies compared to conventional steam cracking of naphtha. The mediocre performance of typical Pd-Ag catalysts for the downstream purification of the substantially higher concentrated acetylene impurities (≥15 vol.-%) in those ethylene streams via selective hydrogenation is yet limiting economic interest. Following the concept of solid catalysts with ionic liquid layer (SCILL), we have modified an intrinsically non-selective palladium catalyst with imidazolium based ionic liquids varying among 10 different anions and investigated them in this reaction. The best performing [C4C1IM][MeSO4]-SCILL reaches an outstanding average ethylene selectivity over 20 h on-stream of 82 % at full acetylene conversion without any sign of deactivation, clearly outperforming conventional Pd-Ag catalysts. By varying parameters like ionic liquid (IL) loading, temperature, feed gas composition, cations, and by using XPS for surface analysis we could gain a very comprehensive understanding of the underlying mechanisms that reduce the competing over-hydrogenation and oligomerisation side-reactions.

Ag-Mediated Growth of Au/Ag-Cu Ternary Heterostructures for Selective Electrochemical CO2 Reduction.

Copper (Cu)-based nanocatalysts play crucial roles in the electrochemical CO2 reduction reaction (ECO2RR) for sustainable energy resources. Particularly, Cu-based nanostructures incorporating Au and Ag are promising, offering enhanced activity, selectivity, and stability. However, precise control over the structure and composition of heterostructures remains challenging, hindering the development of highly efficient catalysts. Herein, we present a silver (Ag) transition-layer-mediated approach to synthesize ternary heterostructures with two specific morphologies, namely, Au/Ag-Cu-side and Au/Ag-Cu-tip, which exhibit different Ag-Cu interface epitaxial patterns. The two heterostructures achieve high C2 product selectivity in ECO2RR. Especially, the Au/Ag-Cu-side structure achieves 50.3% C2 selectivity with 35.5% ethanol, while the tip structure shows higher ethylene selectivity. Our study reveals the impact of the Ag layer in directing deposition sites on heterostructure growth and further facilitating the design of multicomponent Cu-based catalysts with enhanced structural integrity and ECO2RR performance.

Ru-WOX-doped biochar for selective ethylene glycol production from cellulose hydrogenolysis: Unravelling the role of WOX in adjusting acid-metal balance

Ru-WOX composites are usually bi-functional catalysts for cellulose hydrogenolysis, but the proportion/synergism of Ru (metal) and WOX (acidity) are mismatched/unclear, this leads to low ethylene glycol (EG) yield. In this work, we doped Ru‑WOX on low-costed biochar for cellulose hydrogenolysis. The acid-metal balance was adjusted by change the WOX load, and our results show that the activity and EG yield have the order of Ru-30WOX-C > Ru-40WOX-C > Ru-20WOX-C > Ru-10WOX-C, and it is interesting found that a linear relationship between acid/metal ratio and EG yield. Under the optimum conditions (240 °C, 3 MPa and 3 h), Ru-30WOX-C catalyst can achieve 100% cellulose conversion and 61.3% EG yield. 30%WOX facilitates Ru dispersion/reduction, and provides rich acid sites, accompanied by a large number of acid centers (oxygen vacancies), this more easily adsorbed cellulose monomer and activated glucose to glycolaldehyde, and benefit to EG productive. This work provides a guidance to design new bio-functional catalysts for biomass conversion.

Catalytic performance of a single atom Pd1Ag10/Al2O3 catalyst for the selective hydrogenation of acetylene: The role of CO-induced segregation

The single-atom Pd catalysts based on silver-rich bimetallic compositions are known for their extremely high ethylene selectivity in the acetylene hydrogenation reaction; however, their activity is noticeably lower than that of traditional monometallic Pd catalysts. The aim of the work was to apply a method of CO-induced segregation to increase the concentration of single atom Pd1 sites on the surface of Pd1Ag10/Al2O3 catalyst without noticeable formation of multiatomic Pdn (n ≥ 2) ensembles. It has been experimentally established by DRIFTS-CO and XPS methods that the effect of 30 vol% CO exposure temperature on the increase of surface Pd1 sites concentration in the range of 50 to 350 °C has a volcano-like dependence with a maximum at ∼ 200–250 °C. The catalytic tests show a considerable enhancement in activity for samples treated in CO at 200–250 °C (the temperature of 100 % acetylene conversion is reduced by ∼ 30 °C), while the C2H4 selectivity was similar for both freshly reduced and CO-treated catalysts. These results demonstrate the use of CO-induced segregation as a promising method for the controlled increase in the concentration of isolated Pd1 sites to improve the activity of silver-rich palladium catalyst without compromising its selectivity.

Enhancement of ethylene selectivity in chemical looping oxidative dehydrogenation of ethane using manganese-based redox catalysts supported on HY zeolite

As the crucial role of zeolite catalysts becomes increasingly prominent in refining and petrochemical industries, this study introduces a novel application of xMn / HY catalysts in ethane catalytic dehydrogenation via Chemical Looping Oxidative Dehydrogenation (CL-ODH). The synergistic effect of manganese oxides on the HY framework and a moderate amount of acidic sites within the catalyst facilitates the cleavage of C-H bonds and the desorption of olefins, which are vital for advancing ethane CL-ODH. We identified the reasons for maintaining high ethylene selectivity using advanced characterization techniques such as XRD, SEM, TEM, BET, H2-TPR, NH3-TPD, and Py-IR. Notably, under optimized conditions at 700 °C with a gas time-space velocity (GHSV) of 1800 mL·h−1·g−1, the 3Mn/HY catalyst achieved approximately 97.1 % selectivity for ethylene and a 22.7 % conversion of ethane. These findings present a scalable route for ethylene production, showcasing significant industrial relevance by potentially reducing energy costs and improving yield.

Enhancing selectivity through forced dynamic operation with intraparticle diffusion limitations: Ethane oxidative dehydrogenation

During steady state operation (SSO) of industrial fixed-bed reactors diffusion limitations are often present. Well-known impacts include the reduced rate of a positive order reaction and reduced selectivity of the desired intermediate product in a sequential reaction system. This work presents an approach for circumventing diffusion limitations through forced dynamic operation (FDO) of metal oxide catalyzed partial oxidation reactions. Through coupled experiments and modeling, we examine the use of FDO to mitigate selectivity losses of the intermediate product in a parallel-consecutive reaction. With the oxidative dehydrogenation (ODH) of ethane (C2H6) to ethylene (C2H4) over an Al2O3 supported VOx catalyst as the model reaction system, FDO is shown to mitigate undesired C2H4 overoxidation to COx that predominates in steady state diffusion-limited pellets, resulting in C2H4 selectivities that are 15 % (absolute) higher compared to SSO in 2.6 mm catalyst pellets. A kinetic model reveals that FDO beneficially alters the distribution of chemisorbed (O*) and lattice (OL) oxygen, which respectively primarily participate in reactions consuming C2H4 and C2H6. FDO is shown to lead to less detrimental impact of diffusion on the ethylene selectivity and yield compared to SSO. During FDO, generated C2H4 reacts with unselective O*, leaving behind selective OL. The reduced bulk phase O2 in the reductive half cycle leads to accumulation of OL, suppressing C2H4 overoxidation. This effect is amplified via C2H4 trapping in the catalyst pellet. Thus, larger catalyst pellets exhibit selectivities that more rapidly increase with reduction time, inducing higher FDO cycle averages compared to SSO. The findings raise the prospect of applying FDO through feed switching or chemical looping as a way to increase intermediate yield in the class of partial oxidation reactions.

Unlocking Copper-Free Interfacial Asymmetric C-C Coupling for Ethylene Photosynthesis from CO2 and H2O.

Solar-driven carbon dioxide (CO2) reduction into C2+ products such as ethylene represents an enticing route toward achieving carbon neutrality. However, due to sluggish electron transfer and intricate C-C coupling, it remains challenging to achieve highly efficient and selective ethylene production from CO2 and H2O beyond capitalizing on Cu-based catalysts. Herein, we report a judicious design to attain asymmetric C-C coupling through interfacial defect-rendered tandem catalytic centers within a sulfur-vacancy-rich MoSx/Fe2O3 photocatalyst sheet, enabling a robust CO2 photoreduction to ethylene without the need for copper, noble metals, and sacrificial agents. Specifically, interfacial S vacancies induce adjacent under-coordinated S atoms to form Fe-S bonds as a rapid electron-transfer pathway for yielding a Z-scheme band alignment. Moreover, these S vacancies further modulate the strong coupling interaction to generate a nitrogenase-analogous Mo-Fe heteronuclear unit and induce the upward shift of the d-band center. This bioinspired interface structure effectively suppresses electrostatic repulsion between neighboring *CO and *COH intermediates via d-p hybridization, ultimately facilitating an asymmetric C-C coupling to achieve a remarkable solar-to-chemical efficiency of 0.565% with a superior selectivity of 84.9% for ethylene production. Further strengthened by MoSx/WO3, our design unveils a promising platform for optimizing interfacial electron transfer and offers a new option for C2+ synthesis from CO2 and H2O using copper-free and noble metal-free catalysts.

Efficient sorbent/catalyst composites for CO2-mediated oxidative dehydrogenation of ethane via isothermal integrated CO2 capture and utilization

The isothermal integrated CO2 capture and utilization to produce ethylene (ICCU-ODHE) performances of dual functional materials (DFM) were improved by doping five transition metal elements (Fe, Co, Ni, Cu, Zn). The results show that the DFM doped with Zn exhibits excellent ICCU-ODHE performance with an ethylene yield of 35.1 %. The results based on in-situ XPS and DFT calculation show that the doping transition metal elements can reduce the energy barriers for activating ethane and CO2. It is mainly because doping transition metal elements with strong electronegativity can increase the coordinative unsaturated Cr3+ ions to adsorb more ethane molecules, meanwhile, the doping also reduces the charge density of Cr3+ and generates additional unfilled electron orbitals facilitating charge transfer to improve the CO2 and ethane activation. However, the decrease in charge density can increase the difficulty of ethylene desorption and reduce the ethylene selectivity. In addition, the cyclic regeneration experiment shows that the ICCU-ODHE performance of DFM can decrease with the increase of cycles, however, significant performance restoration is achievable after regeneration in the air at 650 °C, attributed to the limited graphitization of coke deposition on the DFM.

Continuous process design of the microwave chemical recycling of waste plastics using microwave-absorbing heating elements

Conventional pyrolysis methods to chemically recycle plastic waste require significant energy input owing to inefficient energy transfer from the heat sources to plastics and the generation of excess CO2. Accordingly, there is an urgent need to develop alternative methods for the chemical recycling of waste plastics to limit global warming. In this study, the use of microwaves (MWs) as an efficient energy source for pyrolysis and chemical recycling. However, because plastic is transparent to MW energy, a method that utilizes carbon materials as MW-absorbing heating elements (MWAHEs) was developed. This method directly converted high-density polyethylene (HDPE) into light chemicals in up to 94% yield with 45% ethylene selectivity. A two-stage pyrolysis system incorporating MWAHE-assisted MW pyrolysis was also developed to produce light chemicals in 95% yield with 49% ethylene selectivity. From a chemical engineering perspective, this two-step pyrolysis system is an efficient and feasible method for producing valuable light olefins. This study also demonstrates that MWAHE assisted MW pyrolysis is effective for the chemical recycling of plastic waste. This study offers potential solutions for the environmental problems posed by plastic waste by developing efficient and scalable methods for its chemical recycling.

Prediction of catalytic performance of metal oxide catalysts for alkyne hydrogenation reaction based on machine learning

In the field of catalyst design, machine learning is gaining significant attention, especially in situations where data is limited. Facing this challenge, we have developed a neural network model that enhances predictive accuracy through the careful selection of catalyst descriptors and feature engineering, aiming to predict the conversion rate and selectivity of the acetylene semi-hydrogenation reaction. Our model has identified promising metal oxide catalysts, such as CuO, ZnO, and V2O5, for the acetylene semi-hydrogenation reaction, and these predictions have been experimentally validated. Among them, CuO achieved an acetylene conversion of 99.6 % and an ethylene selectivity of 90 % at 50–100°C, which is unprecedented at the reaction space velocity we tested. This high activity at relatively low temperatures indicates a more promising industrial application. Looking ahead, machine learning will play a pivotal role in catalyst design, accelerating the discovery and industrial application of new materials.

Multisite-assisted design of asymmetric silicon-bridged diphosphine ligands for selective ethylene tri-/tetramerization

A series of novel silicon-bridged asymmetric diphosphine ligands (PNSiP-type L1-L3 and PCSiP-type L4) and their corresponding Cr(Ⅲ) catalysts have been synthesized and evaluated for ethylene tri-/tetramerization. When DMAO/AlEt3 was used as a co-catalyst, catalyst 1 based on ligand L1, with a cyclopentyl group on the N atom and two methyl groups on the Si atom, showed the highest catalytic activity of 8.21 kg g-1 Cr/h with 90.45 % combined (60.53 % 1-C6= + 29.92 % 1-C8=) selectivity. Moreover, the catalytic system based on catalyst 1 achieved a remarkable selectivity for 1-C8= of 62.58 % at 15 °C, even though polymers were the main products. Catalyst 2 based on ligand L2, bearing a cyclopentyl group at N and one methyl and one phenyl group on the Si moiety, exhibited a catalytic activity of 8.09 kg g-1 Cr/h accompanied with 71.61 % 1-C6= and 14.12 % 1-C8=product selectivity. Catalyst 3 based on ligand L3 having an isopropyl group on the N atom and two methyl groups on the Si atom, displayed 6.95 kg g-1 Cr/h catalytic activity with 69.06 % 1-C6= and 17.88 % 1-C8=product selectivity. Catalyst 4 based on PCSiP-type ligand L4, showed poor catalytic activity and 79.15 % of high 1-C6= selectivity. Compared with the previously reported long-chain Cr(Ⅲ) catalysts based on silicon-bridged diphosphine ligands (PNSiCP-/PCSiCP-type), Cr(Ⅲ) catalysts based on short-chain PNSiP-type and PCSiP-type ligands designed in this work exhibited higher ethylene oligomerization performance. Among them, PNSiP-type ligands are more inclined to generate 1-C8= than PCSiP-type ligand, and reducing the steric bulk of substituents on the Si atom in PNSiP-type ligands is also beneficial for 1-C8= generation. Density functional theory (DFT) calculations also revealed that the PNSiP-type catalysts could exhibit excellent ethylene trimerization performance. The DFT calculations thus provide a theoretical foundation for a deeper understanding of the ethylene tri-/tetramerization mechanism and designing of new ligand structures.

Green hydrogen and acetaldehyde production via photo-induced thermal dehydrogenation of bioethanol over a highly dispersed CuS/ TiO2 catalyst

The emergence of global warming issues has triggered the interest in producing carbon-neutral energy sources and fossil-based chemicals from affordable and renewable feedstocks (e.g., bio-ethanol). Herein, the synthesis of highly dispersed CuS/TiO2 photothermal catalysts is reported for simultaneously converting ethanol into hydrogen and acetaldehyde under simulated sunlight. The catalyst achieved a hydrogen evolution rate of 51.61 mmol g−1 h−1 and an acetaldehyde production rate of 48.63 mmol g−1 h−1, with a maximal acetaldehyde selectivity of 97% among carbon-containing products. Compared to pristine TiO2, the introduction of plasmonic CuS largely extended the light adsorption range and enhanced the photothermal performance, whilst the formation of heterojunction structure improved the charge transfer and separation efficiency. The density functional theory calculation results demonstrate that CuS/TiO2 composite interfaces could significantly lower the activation energy of ethanol dehydrogenation reaction and improve hydrogen evolution reaction ability. This study provides deep insight into understanding and optimizing hot carrier dynamics in photothermal catalytic systems.

Light-driven methanol-to-olefins catalysis over W18O49/SAPO-34 hierarchical nanocomposite with strong photothermal effect

Solar-light-driven photothermal catalysis attracts attention because of the significant energy savings and environmental friendliness compared with thermal catalysis. In the present work, W18O49/SAPO-34 composite materials with hierarchical pore networks were constructed by a simple hydrothermal method, and applied into photothermal catalysis for methanol-to-olefins transformation. In combination of the broaden light absorption of W18O49 and moderate acid site of SAPO-34, the W18O49/SAPO-34 composite showed a rapid temperature rise on the surface of the catalysts due to the strong photo-to-thermal effect of W18O49. Methanol conversion of ∼ 90 % and ethylene selectivity of ∼ 60 % were achieved for the optimized W18O49/SAPO-34 catalyst, much higher than that of bare W18O49 and SAPO-34. The excellent methanol dehydration performance was attributed to the strong plasmonic absorption in the visible and near infrared light, the efficient photothermal conversion effect by localized plasmon heating on the W18O49 nanorods, and synergistic catalysis between W18O49 and SAPO-34. This photothermal catalyst showed great potential in the industrial applications of photocatalytic methanol-to-olefins conversion.

Scaling CO2 Electrolyzer Cell Area from Bench to Pilot.

To contribute meaningfully to carbon dioxide (CO2) emissions reduction, CO2 electrolyzer technology will need to scale immensely. Bench-scale electrolyzers are the norm, with active areas <5 cm2. However, cell areas on the order of 100s or 1000s of cm2 will be required for industrial deployment. Here, we study the effects of increasing cell area, scaling over 2 orders of magnitude from a 5 cm2 lab-scale cell to an 800 cm2 pilot plant-scale cell. A direct scaling of the bench-scale cell architecture to the larger area results in a ∼20% drop in ethylene (C2H4) selectivity and an increase in the parasitic hydrogen (H2) evolution reaction (HER). We instrument an 800 cm2 electrolyzer cell to serve as a diagnostic tool and determine that nonuniformities in electrode compression and flow-influenced local CO2 availability are the key drivers of performance loss upon scaling. Machining of an initial 800 cm2 cell results in a standard deviation in MEA compression that is 7-fold that of a similarly produced 5 cm2 cell (0.009 mm). Using these findings, we redesign an 800 cm2 cell for compression tolerance and increased CO2 transport and achieve an H2 FE in the revised 800 cm2 cell similar to that of the 5 cm2 case (16% at 200 mA cm-2). These results demonstrate that by ensuring uniform compression and fluid flow, the CO2 electrolyzer area can be scaled over 100-fold and retain C2H4 selectivity (within 10% of small-scale selectivity).

Selective hydrogenation of acetylene over Pd/β-Mo2C catalyst: Experimental and theoretical studies

Molybdenum carbide is a promising support to tune the metal reactivity, which originates from the interaction between metal and support. In this work, Pd/β-Mo2C was prepared using a deposition-precipitation method for selective hydrogenation of acetylene. The high temperature calcination is employed to modulate the interaction between Pd and β-Mo2C. The Pd/β-Mo2C catalyst calcined at 600 °C exhibits significant promotion in selective hydrogenation, which shows 100 % acetylene conversion and 81.4 % ethylene selectivity at 160 °C. The activity promotion originates from the enhanced electronic metal-support interaction, which induces a shift of Pd 3d to higher binding energy. Besides, the Pd species become atomically dispersed after calcination. The changes in geometric and electronic structure suppress the formation of Pd hydrides, which consequently inhibits the excessive hydrogenation capacity of Pd. The structure variation also affects the adsorption of ethylene. No strong adsorbed ethylene (di-σ bonded ethylene) can be identified, which is conducive to the improvement of ethylene selectivity. Density functional theoretical (DFT) calculations confirm that Pd on β-Mo2C is positively charged. The desorption energy of C2H4* (0.78 eV) is significantly lower than that of further hydrogenation (1.45 eV), which explains the improved ethylene selectivity of the calcinated catalyst. The present study indicates calcination is an effective method to tune the activity of Pd/β-Mo2C for reactions beyond selective hydrogenation of acetylene.

Performance of PdAu/Al2O3 egg-shell catalyst with isolated Pd1 sites for selective hydrogenation of acetylene

A herein proposed PdAu/Al2O3 egg-shell catalyst for selective acetylene hydrogenation combines two factors to provide perfect performance: isolation of Pd1 active sites by Au and an egg-shell distribution of the active phase across the catalyst pellets. The PdAu/Al2O3 catalyst exhibits high acetylene hydrogenation activity at the level of Pd-catalysts and high intrinsic ethylene selectivity of Au-catalysts.