Active Pd Research Articles

Wide range temperature stability of palladium on ceria-praseodymia catalysts for complete methane oxidation

Catalytic oxidation is the most effective technology to control methane emissions from both mobile and stationary sources. Palladium-based materials are widely viewed as the most active catalysts for the methane abatement reaction, even though the high-temperature PdO/Pd transition is linked to a decrease in catalytic activity. Aimed at minimizing this phenomenon, this work compares the catalytic activity and the thermal stability of different Pd-impregnated cerium-praseodymium mixed oxides prepared via Solution Combustion Synthesis. Although the palladium deposition on pure ceria allows obtaining a highly active system, the introduction of praseodymium enhances the thermal stability of the catalyst in an extended temperature range. X-ray photoelectron spectra show that the presence of praseodymium retains Pd in a more oxidized form, thus stabilizing the high-temperature active phase. This effect, as evident from X-ray diffractograms and Raman analyses, was attributed to a strong interaction of palladium particles with praseodymium, thereby hindering their reduction to the metallic form. Moreover, Pr doping played a significant role during methane oxidation in the presence of 5% H2O, improving both activity and stability compared to Pd on pure ceria. On the whole, Pd/Ce90Pr10 (2 wt% palladium supported on a mixed oxide with a praseodymium content of 10% on a cerium-praseodymium molar basis) was found to be the most promising catalyst amongst the studied materials in both dry and wet conditions, benefitting from the synergistic effect of ceria and praseodymia in improving the Pd activity and stability.

Molecular study of Pompe disease in Egyptian infants

BackgroundPompe disease (PD) is a serious genetic disorder caused by deficiency of acid α-glucosidase (GAA) and subsequent glycogen accumulation inside lysosomes. This study included a cohort of 5 Egyptian infants (1–8 months old) with far lower than average normal GAA activity and clinical signs of PD in 4 of the 5 cases. The fifth case was discovered by newborn screening (NBS). Molecular analysis of the GAA gene was performed to confirm the diagnosis and identify the underlying mutation.ResultsThe study identified the causative mutations [c.1193T > C (p.Leu398Pro), c.1134C > G (p.Tyr378*) & c.1431del (p.Ile477Metfs*43)] in 4 cases. However, molecular analysis reversed the expected pathologic state in the fifth infant, where his reduced enzymatic activity was related to the presence of pseudodeficiency allele c.868A > G (p.Asn290Asp) in addition to heterozygous disease-causing mutation c.2238G > C (p.Trp746Cys).ConclusionThis study presents the first molecular analysis of GAA gene in Egypt and has thrown some light on the importance of PD molecular diagnosis to provide precise diagnosis and enable therapeutic commencement in affected subjects.

Dynamic patterns of teachers’ professional development participation and their relations with socio-demographic characteristics, teacher self-efficacy, and job satisfaction

This study examined the dynamic patterns of teachers' participation in various topics of PD activities to better understand the individual differences in PD experience of teachers. Using Teaching and Learning International Survey 2018 U.S. data (n = 2411), we conducted a latent class analysis and identified five distinct profiles. Moreover, we found that these profiles were associated with teachers' socio-demographics as well as their self-efficacy and job satisfaction. This study adds to the literature by providing a more nuanced understanding of teachers’ PD experience and highlights the importance of supporting teachers to participate in various topics of PD.

Bimetallic PdAg nanoparticles for enhanced electrocatalysis of ethanol oxidation reaction

The exploration of bimetallic Pd-based catalysts has become a hot-spot for the application of high performance electrocatalysts with long term stability in fuels cell. In this work, alloyed Pd x Ag 1 nanoparticles (NPs) ( x = 8, 11, 14, 17, and 20) are synthesized via a solvothermal synthesis approach. The morphologies and compositions of alloyed PdAg NPs are characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The optimized Pd 14 Ag 1 NPs exhibited excellent current activity in ethanol oxidation reaction (EOR) of 2430 mA mg −1 in an alkaline ethanol solution, 3.3 times higher than commercial Pd/C counterpart (727 mA mg −1 ), closely related to the change of electron structure and surface active sites. In addition, compared with other PdAg NPs and commercial Pd/C catalysts, Pd 14 Ag 1 NPs performs better antitoxicity, lower reaction barrier, and better long-term stability. Experimental results show that higher catalytic temperature, higher pH values, and higher ethanol concentration should favor the oxidation of ethanol. • Alloyed Pd x Ag 1 nanoparticles are synthesized via solvothermal synthesis. • The catalytic activity of Pd 14 Ag 1 NPs is much higher than commercial Pd/C. • The effects of temperature as well as concentration of KOH/C 2 H 5 OH were discussed.

Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au-Pd Nanoparticles through Redox Switching of SnOx.

A balance between catalytic activity and product selectivity remains a dilemma for the partial oxidation processes because the products are prone to be overoxidized. In this work, we report on the partial oxidation of benzyl alcohol using a modified catalyst consisting of nanosized Au-Pd particles (NPs) with tin oxide (SnOx) deposited on a mesoporous silica support. We found that the SnOx promotes the autogenous reduction of PdO to active Pd0 species on the Au-Pd NP catalyst (SnOx@AP-ox) before H2 reduction, which is due to the high oxophilicity of Sn. The presence of active Pd0 species and the enhancement of oxygen transfer by SnOx led to high catalytic activity. The benzaldehyde selectivity was enhanced with the increase of SnOx content on catalyst SnOx@AP-ox, which is ascribed to the modulated affinity of reactants and products on the catalyst surface through the redox switching of Sn species. After H2 reduction, SnOx was partially reduced and Au-Pd-Sn alloy was formed. The formation of Au-Pd-Sn alloy weakened both the catalytic synergy of Au-Pd alloy NPs and the adsorption of benzyl alcohol on the reduced catalyst, thus leading to low catalytic activity.

Pd(4-R3Si-IPr)(allyl)Cl]/K2CO3/EtOH: A highly effective catalytic system for the Suzuki-Miyaura cross-coupling reaction

A series of R3Si-NHC-Pd complexes 1Pd-7Pd was successfully tested as a pre-catalyst for the Suzuki-Miyaura cross-coupling reaction of aryl chlorides and arylboronic acid derivatives to form a wide range of valuable biphenyl products. Use of the readily available weakly basic potassium carbonate as a base and the highly polar protic ethanol as the reaction solvent gave the target coupling products in good-to-excellent yields. The experimental data pointed to the crucial importance of the preliminary pre-catalyst activation step [i.e., the conversion of Pd(II) to Pd(0)], which is remarkably facilitated by the electron-donating trialkylsilyl groups on the NHC ligands of 1Pd–7Pd, thereby rendering them superior compared to the commercially available IPr-Pd complexes. Computational analysis revealed the mechanism of the Pd(II)→Pd(0) activation step, demonstrating the critical role of the reaction solvent and the base in the preference of our 1Pd–7Pd pre-catalysts, for which this step is both thermodynamically and kinetically more feasible.

Pharmacodynamic measures within tumors expose differential activity of PD(L)-1 antibody therapeutics

Macromolecules such as monoclonal antibodies (mAbs) are likely to experience poor tumor penetration because of their large size, and thus low drug exposure of target cells within a tumor could contribute to suboptimal responses. Given the challenge of inadequate quantitative tools to assess mAb activity within tumors, we hypothesized that measurement of accessible target levels in tumors could elucidate the pharmacologic activity of a mAb and could be used to compare the activity of different mAbs. Using positron emission tomography (PET), we measured the pharmacodynamics of immune checkpoint protein programmed-death ligand 1 (PD-L1) to evaluate pharmacologic effects of mAbs targeting PD-L1 and its receptor programmed cell death protein 1 (PD-1). For PD-L1 quantification, we first developed a small peptide-based fluorine-18-labeled PET imaging agent, [18F]DK222, which provided high-contrast images in preclinical models. We then quantified accessible PD-L1 levels in the tumor bed during treatment with anti-PD-1 and anti-PD-L1 mAbs. Applying mixed-effects models to these data, we found subtle differences in the pharmacodynamic effects of two anti-PD-1 mAbs (nivolumab and pembrolizumab). In contrast, we observed starkly divergent target engagement with anti-PD-L1 mAbs (atezolizumab, avelumab, and durvalumab) that were administered at equivalent doses, correlating with differential effects on tumor growth. Thus, we show that measuring PD-L1 pharmacodynamics informs mechanistic understanding of therapeutic mAbs targeting PD-L1 and PD-1. These findings demonstrate the value of quantifying target pharmacodynamics to elucidate the pharmacologic activity of mAbs, independent of mAb biophysical properties and inclusive of all physiological variables, which are highly heterogeneous within and across tumors and patients.

Immobilization of Pd(0) nanoparticles on gemini quaternary ammonium functionalized polyacrylonitrile fibers as highly active catalysts for heck reactions and 4-nitrophenol reduction

Palladium salts and Pd(0) nanoparticles were immobilized on a series of amine and quaternary ammonium functionalized polyacrylonitrile fibers (PANFs) to prepare functionalized fiber catalysts. The catalytic activities of these materials for Heck reaction were investigated. Among which, the Gemini quaternary ammonium fiber immobilized Pd(0) nanoparticles catalyst PANGQAF-Pd(0) exhibited the best catalytic activity, which was able to effectively catalyze Heck reaction and 4-nitrophenol (4-NP) reduction with high yields of 76–99%. And the catalyst can tolerate an extensive scope of substrates under mild reaction conditions. In addition, PANGQAF-Pd(0) was easily recovered, and it can be reused 10 times with little decrease in catalytic activity and low Pd leaching (only 3.69%). The experimental results confirmed that Pd(II) was converted into Pd(0) during the coupling reactions, which helped to promote the reaction. This explains why the catalytic activity of PANF-immobilized Pd(0) is better than that of PANF-immobilized Pd(II). Accordingly, possible mechanisms for the catalytic Heck reaction and reduction reaction of PANGQAF-Pd(0) were proposed.

Experimental evidence for the direct involvement of Pd(0) and Pd(II) anionic phosphine complexes in the Mizoroki–Heck coupling reaction

The role of ionic Pd species in the catalytic systems used for cross-coupling reactions has been revised in recent years, mainly utilizing in situ analytical techniques to detect catalyst species in the reaction mixture. The possible inclusion of phosphine molecules in the active Pd complexes is still debated. We have carried out a comparative study on the differential selectivity of the Mizoroki–Heck reaction with competition between two aryl halides or two alkenes to elucidate the active Pd species in different types of catalytic systems, including those favoring the formation of ionic complexes. The sensitivity of the reaction differential selectivity of two competing aryl halides to the additives of tertiary phosphine and halide salts points to the catalytic activity of anionic Pd(0) complexes containing at least one phosphine ligand when the phosphine-containing catalytic systems are used. The changes of the reaction differential selectivity of two competing alkenes to phosphine and halide salt allow to propose the entrance of both phosphine and halide ions into the coordination sphere of active Pd(II) complexes possessing anionic character. In addition, evidence for the effect of phosphine ligand and salt additives on the composition of the active Pd complexes that determine the regioselectivity of the reaction is presented. The data obtained indicate the decisive role of anionic Pd species in the Mizoroki–Heck reaction using both phosphine-free and phosphine-containing catalytic systems.

Metastable Nanoporous Palladium Evolving from Palladium Nanocrystals

AbstractNanoporous metals can be used in many technological applications, and continuous interest has been focused on their preparation. In this study, we describe a different type of preparation method, in which nanoporous palladium (Pd) is prepared from Pd nanocrystals by the elimination of stabilizers. The resulting nanoporous Pd has a bimodal pore structure with an extensive surface area, and its surfaces are electrochemically accessible and exhibit higher catalytic activity toward ethanol electrooxidation than that of the commercial Pd black catalyst. An interesting feature is that the atomic surface structure can be sensitively altered by the preparation temperature and solvent, thereby increasing the catalytic activity of nanoporous Pd. The proposed method is simple and available for mass production and is expected to be a new alternative for producing electrochemically active nanoporous Pd.

Facile and fast decoration of SnO2 nanowires with Pd embedded SnO2-x nanoparticles for selective NO2 gas sensing

The typical methods used to improve the sensing properties of metal oxide nanowire-based gas sensors include decoration of a metal catalyst on the surface of nanowires or generation of surface defects. In this study, we suggest a process for preparing a Pd metal catalyst surrounded in SnO2-x with a large number of structural defects on the surface of SnO2 nanowires for gas sensing applications. Initially, SnO2 nanowires were prepared using a simple vapor-liquid-solid method and Pd-embedded SnO2-x-decoration was achieved by flame chemical vapor deposition. Gas sensing studies demonstrated the promising effects of Pd-embedded SnO2-x-decoration. The underlying sensing mechanism was studied in detail and explained in terms of generation of oxygen defects, catalytic activity of Pd, and formation of heterojunctions in the sensing material. The results of the present study clearly demonstrate the usefulness of this simple and fast approach to significantly enhance the gas sensing properties of metal oxide nanowires.

Attempt to Understand the Degradation Process of GFRP Insulator with Void Defect at Cryogenic Temperature

Glass Fiber Reinforced Plastic (GFRP) is usually employed as the insulator material of superconducting cable terminal, owing to its excellent mechanical properties and insulation strength at cryogenic temperature. However, in the presence of a void defect, both the insulation life span and mechanical strength of GFRP decrease significantly at superconducting temperature conditions. In this paper, efforts have been made to investigate the degradation process of GFRP at cryogenic temperature and give insight into its degradation mechanism. By comparing PD activities at 278.7 K, 223 K and 153 K in initial phase of aging, it is found that PDs are inclined to be inhibited at lower temperature. Experiments indicate that the deposited charge accumulation and mechanical properties degradation, instead of chemical aging and PD energy, play a crucial part in dielectric degradation. At cryogenic temperatures, the local heat accumulation brought by PDs increases the material internal mechanical stress, and the accumulation of deposited charges causes instantaneous energy release. On the basis of the decrease of the mechanical properties of the material, the crack expands rapidly, which leads to the dielectric failure of the material. In conclusion, the degradation of GFRP at cryogenic temperature is the result of the combined effects of deposited charge accumulation and mechanical properties decline.

Integrating perspectives of patients, healthcare professionals, system developers and academics in the co-design of a digital information tool.

Patients diagnosed with cancer who are due to commence radiotherapy, often, despite the provision of a considerable amount of information, report a range of unmet information needs about the treatment process. Factors such as inadequate provision of information, or the stressful situation of having to deal with information about unfamiliar things, may influence the patient's ability to comprehend the information. There is a need to further advance the format in which such information is presented. The composition of information should be tailored according to the patient's individual needs and style of learning. The PD methodology is frequently used when a technology designed artefact is the desired result of the process. This research is descriptive of its kind and provides a transparent description of the co-design process used to develop an innovative digital information tool employing PD methodology where several stakeholders participated as co-designers. Involving different stakeholders in the process in line with recommended PD activities enabled us to develop a digital information tool that has the potential to be relevant and user-friendly for the ultimate consumer. Facilitating collaboration, structured PD activities can help researchers, healthcare professionals and patients to co-design patient information that meets the end users' needs. Furthermore, it can enhance the rigor of the process, ensure the relevance of the information, and finally have a potential to employ a positive effect on the reach of the related digital information tool.

Highly dispersed Pd nanoparticles for electrocatalytic dechlorination: Positive and negative effects of carbon supports

It is generally known that carbon supports with a large surface area are essential for dispersion of Pd catalysts and adsorption of pollutants (e.g., chlorinated compounds), thus enabling enhanced mass transfer and increased reaction kinetics. However, we demonstrate that, in spite of contributing to achieving highly dispersed Pd nanoparticles, a high-surface-area carbon support favoring fast adsorption of 2,4-dichlorophenol negatively impacts the catalytic activity of Pd. Comparisons of catalytic performance between Pd/activated carbon (AC) catalysts with different mass loadings in a 3D electrochemical dechlorination reactor suggested that Pd(60%)/AC outperformed Pd(10%)/AC, although the latter had smaller Pd catalysts and the amount of Pd was same in these experiments. We found that the dechlorination rate constant was inversely correlated to the adsorption rate constant at Pd loadings from 10% to 60%. We further verified that the use of C3N4, an optimal carbon support with low surface area that allows good dispersion of Pd nanoparticles (10%), is critical in accelerating the dechlorination reaction kinetics due to the improved accessibility of active sites to the pollutants. This study provides information on how to select optimal supporting materials with desirable features that avoid catalyst aggregation and pre-adsorption of pollutants when the supported Pd catalysts are used as the moveable particle electrodes.

Small heterodimer partner (SHP) aggravates ER stress in Parkinson\u2019s disease-linked LRRK2 mutant astrocyte by regulating XBP1 SUMOylation

BackgroundEndoplasmic reticulum (ER) stress is a common feature of Parkinson’s disease (PD), and several PD-related genes are responsible for ER dysfunction. Recent studies suggested LRRK2-G2019S, a pathogenic mutation in the PD-associated gene LRRK2, cause ER dysfunction, and could thereby contribute to the development of PD. It remains unclear, however, how mutant LRRK2 influence ER stress to control cellular outcome. In this study, we identified the mechanism by which LRRK2-G2019S accelerates ER stress and cell death in astrocytes.MethodsTo investigate changes in ER stress response genes, we treated LRRK2-wild type and LRRK2-G2019S astrocytes with tunicamycin, an ER stress-inducing agent, and performed gene expression profiling with microarrays. The XBP1 SUMOylation and PIAS1 ubiquitination were performed using immunoprecipitation assay. The effect of astrocyte to neuronal survival were assessed by astrocytes-neuron coculture and slice culture systems. To provide in vivo proof-of-concept of our approach, we measured ER stress response in mouse brain.ResultsMicroarray gene expression profiling revealed that LRRK2-G2019S decreased signaling through XBP1, a key transcription factor of the ER stress response, while increasing the apoptotic ER stress response typified by PERK signaling. In LRRK2-G2019S astrocytes, the transcriptional activity of XBP1 was decreased by PIAS1-mediated SUMOylation. Intriguingly, LRRK2-GS stabilized PIAS1 by increasing the level of small heterodimer partner (SHP), a negative regulator of PIAS1 degradation, thereby promoting XBP1 SUMOylation. When SHP was depleted, XBP1 SUMOylation and cell death were reduced. In addition, we identified agents that can disrupt SHP-mediated XBP1 SUMOylation and may therefore have therapeutic activity in PD caused by the LRRK2-G2019S mutation.ConclusionOur findings reveal a novel regulatory mechanism involving XBP1 in LRRK2-G2019S mutant astrocytes, and highlight the importance of the SHP/PIAS1/XBP1 axis in PD models. These findings provide important insight into the basis of the correlation between mutant LRRK2 and pathophysiological ER stress in PD, and suggest a plausible model that explains this connection.

Comparative Study of the Efficiency of Different Noble Metals Supported on Hydroxyapatite in the Catalytic Lean Methane Oxidation under Realistic Conditions.

The combustion of lean methane was studied over palladium, rhodium, platinum, and ruthenium catalysts supported on hydroxyapatite (HAP). The samples were prepared by wetness impregnation and thoroughly characterized by BET, XRD, UV-Vis-NIR spectroscopy, H2-TPR, OSC, CO chemisorption, and TEM techniques. It was found that the Pd/HAP and Rh/HAP catalysts exhibited a higher activity compared with Pt/HAP and Ru/HAP samples. Thus, the degree of oxidation of the supported metal under the reaction mixture notably influenced its catalytic performance. Although Pd and Rh catalysts could be easily re-oxidized, the re-oxidation of Pt and Ru samples appeared to be a slow process, resulting in small amounts of metal oxide active sites. Feeding water and CO2 was found to have a negative effect, which was more pronounced in the presence of water, on the activity of Pd and Rh catalysts. However, the inhibiting effect of CO2 and H2O decreased by increasing the reaction temperature.

Self-Powered Broadband Photodetector and Sensor Based on Novel Few-Layered Pd3(PS4)2 Nanosheets.

Optoelectronics and sensing devices are of enormous importance in our modern lives, which has propelled the scientific community to explore new two-dimensional (2D) nanomaterials to meet the requirements of future devices. Herein, we present the exfoliation of palladium thiophosphate (Pd3(PS4)2) by mechanical shear force exfoliation. The Pd3(PS4)2-based photoelectrochemical (PEC) device demonstrated self-powered broadband photodetection in the range of 385-940 nm with an unprecedented responsivity of 2 A W-1 and a specific detectivity of about 8.67 × 1011 cm Hz1/2 W-1 under the illumination of 420 nm LED light. The crucial parameters such as photoresponsivity, response, and recovery time of the device can be controlled by an externally applied voltage and the analyte concentration. Moreover, Pd3(PS4)2-based vapor-sensing devices exhibited frequency-dependent selective acetone sensing in the presence of other organic vapors with an ultrafast response and a recovery time of less than 1 s. Finally, the photocatalytic activity of Pd3(PS4)2 was revealed, which can be attributed to the presence of an appropriate band alignment with the catalytic activity of Pd. This novel material with the aforementioned fascinating phenomenon will pave the way toward practical future applications in optoelectronics and sensing.

Sensitive H2 gas sensors based on SnO2 nanowires

Sensitive H2 gas sensors are highly desirable for the prediction and early-warning of H2 leakage. Low-dimensional nanostructures of metal oxide semiconductor emerge as promising materials candidates, but it remains a challenge to preserve the nanostructures in the real sensors. In this work, we demonstrated highly sensitive H2 gas sensors based on porous network of SnO2 nanowires that exhibited ultrasmall diameter ∼ 2 nm. Colloidal SnO2 nanowires synthesized via a solvothermal process were drop-coated onto the commercial alumina substrates, followed by in-situ annealing treatment at 350 °C to remove the surface ligands. The sensors exhibited sensitive response with linear dependence on the H2 gas concentration ranging from 2 ppm to 100 ppm when operated at 250°C. Typically, the sensor had a response of 13 toward 40 ppm of H2, with the response and recovery time being 15 s and 31 s, respectively. To further improve the sensor performance, Palladium doped SnO2 nanowires were thoroughly investigated. It’s shown that, the operating temperature of the sensor decreased from 250 °C to 150 °C after Pd doping, and the response and recovery time decreased to 6 s/3 s. The superb sensitivity was attributed to the enhanced gas reception, electron transport as well as utility factor owing to the network nanostructure of ultrathin SnO2 nanowires and catalytic activity of Pd, according to theoretical calculation and adsorption kinetics studies. Combined with the excellent solution processability, the colloidal SnO2 nanowires are potentially attractive for next-generation gas sensors with lower power consumption and integration with silicon-based substrates.

Activity of Pdn (n = 1–5) Clusters on Alumina Film on Ni3Al(111) for CO Oxidation: A Molecular Beam Study

Single atom catalyst (SAC) is a vivid new area of research in catalysis. However, the activity in CO oxidation of isolated Pt or Pd atoms, generally supported on an oxide powder, is still controversial. Furthermore, the steady state activity of few atoms clusters is still not yet quantitatively known. In this work we study, by molecular beam reactive scattering (MBRS), the activity of Pd$_{\rm n}$ ($n$ = 1-5) clusters, grown on a nanostructured alumina films on a Ni$_3$Al(111) surface. It is shown that the single atoms are not active at 473 K but they diffuse and coalesce at 533K forming larger clusters. The activity of a cluster is proportional to the number of atoms it contains (n=2-5). At 533 K, the activity per (surface-) atom, which is the turnover frequency (TOF), is constant. Its value is close to those obtained for large clusters of 181$\pm$13 atoms and Pd (111) extended surfaces, in the same experimental conditions.

Palladium Nanoparticles on Covalent Organic Framework Supports as Catalysts for Suzuki–Miyaura Cross-Coupling Reactions

Suzuki–Miyaura cross-coupling (SMC) reaction by palladium (Pd) catalysis is widely used in cross-coupling chemistry synthesis for C—C bond formation, yet the biaryl products are generally lacking halo substituents due to highly active palladium species. Suitable catalysts according to this property for the region-selective SMC synthesis of biaryl derivatives with halo substituents did not receive due and sufficient attention. Here, we report the facile synthesis of a covalent organic frameworks (COFs)-supported nanoparticles Pd catalyst that can region-selectively catalyze the SMC reaction of aryl boronic acids and aryl halides, especially with halogenated aryl boronic acids. The methodology exhibits mild operating conditions, broad functional group tolerance, and environmental friendliness and can be strategically applied for cross-coupling scenarios governed by sequential transition metal catalysts to build with or without a halo-substituted moiety. The Pd/COF-SMC nanoparticles catalysts are stable and reusable and succeed in synthesizing halo-substituted biaryl products in excellent yield, which avoids the homocoupling of halogenated aryl boronic acid. The most outstanding advantage is the precise regulation of nanoparticles Pd activity with the well-designed COF ligand.