Pd Component Research Articles

Fiber-supported Pd Catalysts for Cross-coupling Reaction of Aromatic and Aliphatic Terminal Alkynes

Increasing the efficiency of cross-coupling reaction under mild condition and easy catalyst separation is a key issue in the realistically chemical industry application. Here, we report that the fiber-supported Pd catalyst shows a high activity and selectivity for the cross-coupling reaction of terminal alkynes. The yield of the asymmetric 1,3-diyne can reach 83% at 80 °C and 4 h reaction time in N,N-dimethylacetamide (DMAc), and about 87% selectivity. XPS, EDS and SEM results show that Pd metal ions are successfully loaded onto the fiber surface and are reduced to produce active component of Pd (0) by terminal alkyne in reaction. We consider that Pd (0) is the active center of the catalytic cycle, the coordination of the fibers can stabilize Pd particles on the supports and increases the catalytic activity of Pd catalysts. Cu (I) plays a synergistic catalytic role. This study provides an alternative pathway for the high efficient cross-coupling reaction.

Perceptual learning induces active suppression of physically nonsalient shapes.

Visual attention can be attracted by salient-but-irrelevant features, a phenomenon called attentional capture. Accompanying attentional capture, a top-down inhibitory mechanism is usually enacted to suppress the attentional shift. Our recent study showed that a physically nonsalient shape, which may be considered as a conjunction of basic features within the form domain, can also provoke a robust capture of attention as a consequence of perceptual learning, supporting an important role of prior experience in attentional deployment. It remains unclear, however, whether prior experience can also induce attentional suppression to conjunctions of features. Here, we examine whether and in which condition the brain would initiate an active suppression process to a physically nonsalient shape which has acquired an ability to capture attention after perceptual learning. We show that detectability of a shape after perceptual learning may be a key factor determining whether the shape would be actively suppressed or not. After extensive training as a target in visual search, a physically nonsalient shape could elicit an N2pc component when it was a distractor in a visual search task or a peripheral irrelevant stimulus in a central focused attention task, indicating a capture of attention induced by perceptual learning. Following the N2pc component, a Pd component would be elicited by the trained shape only if its detectability is relatively high. These findings suggest that an active suppression process could be applied not only to salient features but also to physically nonsalient shapes. A physically nonsalient shape could improve its salience through perceptual learning and would be actively suppressed when its learned salience reaches a certain level.

Force ripple compensation in a PMLSM position servo system using periodic adaptive learning control

Force ripple deteriorates the performance of permanent magnet linear synchronous motor (PMLSM) servo systems. Using a model reference adaptive control and periodic adaptive learning control (MRAC–PALC) algorithm, this paper presents a novel compensation method to eliminate the influence of force ripple on the system performance of a position servo system under repetitive motion tasks. The key idea of the proposed method is to utilize the periodic characteristics of both force ripple and system motion. The controller consists of four components: a PD component, a feedforward component, a velocity feedback component and an MRAC–PALC compensator. The first three components are designed in a conventional way. The compensator is divided into two parts: in the 0th-iteration, an MRAC algorithm is employed to obtain the initial information, and in the ith-iteration (i≥ 1), a PALC algorithm is used to learn from the information obtained in the previous period and update the controller parameters for estimating force ripple. Moreover, a theoretical stability analysis is given via Lyapunov stability theorem, and some comparative results are provided through simulations and experiments.

Insight into restructuring of Pd-Au nanoparticles using EXAFS

We acquired Pd K-edge and Au L3-edge EXAFS spectra of two libraries of titania-supported Pd-doped Au nanoparticle catalysts representing the as-prepared and post-catalysis state. The nanoparticles have narrow particle size distributions, in the range 2.8–6.6 nm, and were synthesized to preferentially locate the palladium atoms on the surface of a gold core, with Pd mole fractions of 1.4–38%. EXAFS spectra of both the as-prepared samples and post-catalysis Pd-Au particles were collected and modeled. EXAFS refinement of all samples showed contributions from both Pd-Au and Pd-Pd scattering paths, revealing that Pd and Au components alloyed together. Pd was in a partially oxidized state as evidenced by a Pd-O scattering contribution, unlike Au. Overlaying measured coordination numbers from the libraries with predicted values, using models of surface and bulk alloying, showed that Pd restructures among Au as a result of exposure to the reaction conditions.

Different ecological processes determined the alpha and beta components of taxonomic, functional, and phylogenetic diversity for plant communities in dryland regions of Northwest China.

Drylands account for more than 30% of China’s terrestrial area, while the ecological drivers of taxonomic (TD), functional (FD) and phylogenetic (PD) diversity in dryland regions have not been explored simultaneously. Therefore, we selected 36 plots of desert and 32 plots of grassland (10 × 10 m) from a typical dryland region of northwest China. We calculated the alpha and beta components of TD, FD and PD for 68 dryland plant communities using Rao quadratic entropy index, which included 233 plant species. Redundancy analyses and variation partitioning analyses were used to explore the relative influence of environmental and spatial factors on the above three facets of diversity, at the alpha and beta scales. We found that soil, climate, topography and spatial structures (principal coordinates of neighbor matrices) were significantly correlated with TD, FD and PD at both alpha and beta scales, implying that these diversity patterns are shaped by contemporary environment and spatial processes together. However, we also found that alpha diversity was predominantly regulated by spatial structure, whereas beta diversity was largely determined by environmental variables. Among environmental factors, TD was most strongly correlated with climatic factors at the alpha scale, while with soil factors at the beta scale. FD was only significantly correlated with soil factors at the alpha scale, but with altitude, soil and climatic factors at the beta scale. In contrast, PD was more strongly correlated with altitude at the alpha scale, but with soil factors at the beta scale. Environment and space explained a smaller portion of variance in PD than in TD and FD. These results provide robust evidence that the ecological drivers of biodiversity differ among different scales and facets of diversity. Future research that focuses on the comparisons among TD, FD and PD would likely provide new insights into elucidating the underlying community assembly.

An efficient thin-walled Pd/polypyrrole hybrid nanotube biocatalyst for sensitive detection of ascorbic acid

Controllable fabrication of novel and uniform noble metal nanoparticles on a specific support with a superior catalytic or electrocatalytic performance is of significantly importance for practical applications. In this report, we demonstrated an effective way to fabricate uniform thin-walled Pd/polypyrrole (PPy) hollow nanotubes. The prepared Pd/PPy hybrid nanotubes exhibited an excellent peroxidase-like activity to oxidize a typical peroxidase substrate such as 3,3′,5,5′-tetramethylbenzidine in comparison with traditional Pd/C and Pd black catalysts. The outstanding catalytic activity of the Pd/PPy hybrid nanotubes for peroxidase mimicking could be resulting from their unique hollow characteristic and an interfacial effect between PPy and Pd components. Based on the favorable catalytic property of the Pd/PPy hybrid nanotubes, a convenient and rapid colorimetric way to sensitively determine ascorbic acid has been presented. The detection limit was around 0.062 μM and an excellent selectivity was also achieved. The developed detection system in this study could be extended to the fields of bioscience and biotechnology with promising prospects.

Electrophysiological correlates of active suppression and attentional selection in preview visual search

Advance preview of a subset of distractor objects improves the efficiency of visual search performance, but the causes and mechanisms of such preview benefits remain unclear. Here, we employed event-related potential (ERP) markers of the selective processing of preview displays and full search displays in lateralised preview search tasks where only one side of the search displays was task-relevant. Preview displays elicited a sustained positivity contralateral to the relevant side (PD component), indicative of the active suppression of distractor objects on this side. Lateralised ERP components to full search displays revealed qualitative differences between attentional selection processes on preview as compared to no-preview trials. When search displays were preceded by preview displays, attention was directly allocated to target objects, while distractors remained unattended. When all search display objects were presented simultaneously (no-preview), attention was directed non-selectively to objects on the task-relevant side, even when no target was present. These results suggest that behavioural preview effects in visual search can be accounted for by the inhibition of previewed distractors, and the subsequent rapid attentional selection of target objects on preview trials.

Statistical learning shapes distractor suppression

Even though traditionally attentional control is considered to be the result of the interaction between top-down and bottom-up mechanisms, Awh, Belopolsky and Theeuwes (2012, TICS) have suggested a theoretical framework in which this division is argued to be incomplete. They argued that the history of attentional deployments can elicit lingering selection biases, which are unrelated to top-down goals or the physical salience of items. Whereas previous work has primarily focused on target selection, here we investigated whether implicitly learned statistical regularities can influence distractor processing. We used the additional singleton task in which participants search for a salient shape singleton while ignoring a color distractor singleton. This color distractor was systematically presented more often in one location than in all other locations. Using measures of behavior, we demonstrate that for this high-probability location, both the amount of attentional capture by distractors and the efficiency of selecting the target were reduced. Measures of brain activity, specifically the Pd (distractor positivity) and N2pc components of the event-related potential, were used to track the allocation of attention and suppression to lateralized positions in the arrays. We find evidence for a Pd-like component for the high probability location, even though both the target and the distractor were presented on the vertical meridian (top and bottom) and thus could not themselves elicit a lateralized component in the ERP. When the distractor was presented at the lateralized high probability location, this also generated a Pd, while a distractor presented at a low probability location generated an N2pc. The same was found for when the target was presented at the high versus low lateralized probability location. We interpret these findings as evidence that spatial statistical regularities influence distractor processing through inhibition of high probability locations.

Hydrogen production on Pd0.01Zn0.29Mg0.7Al2O4 spinel catalyst by low temperature ethanol steam reforming reaction

This study investigated the low-temperature ethanol steam reforming (LTESR) performance of a Pd0.01Zn0.29Mg0.7Al2O4 catalyst. Although it was present in a very small amount, the Pd component was the key to the partial CO-water gas shift and CO-methanation that, eventually, helped to increase the yield of H2 during LTESR. An 80% yield of H2 was maintained even after 30 h at 450 °C on the Pd0.01Zn0.29Mg0.7Al2O4 catalyst with 100% ethanol conversion. Furthermore, the spinel structure of the catalyst remained unchanged after the reaction, and there was no increase in size owing to particle-to-particle aggregation. This study demonstrated that the Pd and Zn components could be stably located in the spinel structure of the MgAl2O4 with no sintering of the particles. Moreover, the oxygen transfer capacity of the MgAl2O4 spinel structure helped maintain the catalytic performance for long time periods by transferring oxygen to the reduced catalytic metal species (Zn or Pd) during the reaction, even though this induced oxygen defects in the spinel crystal. Overall, improved catalyst activity and an extended catalyst lifespan were observed.

Combined Electrophysiological and Behavioral Evidence for the Suppression of Salient Distractors.

Researchers have long debated how salient-but-irrelevant features guide visual attention. Pure stimulus-driven theories claim that salient stimuli automatically capture attention irrespective of goals, whereas pure goal-driven theories propose that an individual's attentional control settings determine whether salient stimuli capture attention. However, recent studies have suggested a hybrid model in which salient stimuli attract visual attention but can be actively suppressed by top-down attentional mechanisms. Support for this hybrid model has primarily come from ERP studies demonstrating that salient stimuli, which fail to capture attention, also elicit a distractor positivity (PD) component, a putative neural index of suppression. Other support comes from a handful of behavioral studies showing that processing at the salient locations is inhibited compared with other locations. The current study was designed to link the behavioral and neural evidence by combining ERP recordings with an experimental paradigm that provides a behavioral measure of suppression. We found that, when a salient distractor item elicited the PD component, processing at the location of this distractor was suppressed below baseline levels. Furthermore, the magnitude of behavioral suppression and the magnitude of the PD component covaried across participants. These findings provide a crucial connection between the behavioral and neural measures of suppression, which opens the door to using the PD component to assess the timing and neural substrates of the behaviorally observed suppression.

Low cost fabrication of highly sensitive ethanol sensor based on Pd-doped α-Fe2O3 porous nanotubes

Pure and Pd-doped α-Fe2O3 porous nanotubes (PNTs) are synthesized by a facile electrospinning approach. Different Pd dopant concentrations are introduced to investigate the dopant’s role in sensing performance. The structures and chemical compositions of the as-prepared products are examined using a series of characterization methods including XRD, EDS, SEM, TEM, XPS and BET. The gas-sensing properties of the sensor based on above PNTs are studied. And the results reveal that, compared with pure α-Fe2O3, the 3.0 wt% Pd-doped α-Fe2O3 PNTs sensors exhibit superior performance in ethanol detection (at 240 °C). The highest sensitivity reaches 65.4 for 50 ppm ethanol and the detection limit is as low as 0.1 ppm. In addition, the sensors also show excellent selectivity, good long-term stability and as well as rapid response/recovery time (8 s/30 s, respectively) to ethanol. The improvement of sensing performance is mainly attributed to the dramatic sensitization of the additional Pd components.

Neural Evidence for the Contribution of Active Suppression During Working Memory Filtering.

In order to efficiently process incoming visual information, selective attention acts as a filter that enhances relevant and suppresses irrelevant information. In this study, we used an event-related potential (ERP) approach with systematic lateralization to investigate enhancement and suppression during encoding of information into visual working memory (WM) separately. We used a change detection task in which observers had to memorize some items while ignoring other items. We found that the to-be-ignored items elicited a PD component in the ERP, suggesting that irrelevant information is actively suppressed from WM. The PD amplitude increased with distractor load and decreased with the ability to group distractors according to Gestalt principles. This suggests that the PD can be used as an indicator of how efficiently items can be suppressed from entering WM. Furthermore, while lateral memory-targets elicited a "traditional" CDA (starting ~300 ms), lateral memory-distractors elicited a sustained positivity contralateral to memory-distractors (CDAp, starting ~400 ms). In sum the results suggest that inhibition of irrelevant information is an important factor for efficient WM and is reflected in spontaneous (PD) and sustained suppression (CDAp).

Design of atomically precise Au2Pd6nanoclusters for boosting electrocatalytic hydrogen evolution on MoS2

A new Au–Pd alloy nanocluster (NC) – Au2Pd6S4(PPh3)4(C6H4F2S)6is synthesized. The NC is applied to enhance the electrocatalytic HER activity of MoS2compared with a single Pd or Au component.

Scopolamine Reduces Electrophysiological Indices of Distractor Suppression: Evidence from a Contingent Capture Task.

Limited resources for the in-depth processing of external stimuli make it necessary to select only relevant information from our surroundings and to ignore irrelevant stimuli. Attentional mechanisms facilitate this selection via top-down modulation of stimulus representations in the brain. Previous research has indicated that acetylcholine (ACh) modulates this influence of attention on stimulus processing. However, the role of muscarinic receptors as well as the specific mechanism of cholinergic modulation remains unclear. Here we investigated the influence of ACh on feature-based, top-down control of stimulus processing via muscarinic receptors by using a contingent capture paradigm which specifically tests attentional shifts toward uninformative cue stimuli which display one of the target defining features In a double-blind, placebo controlled study we measured the impact of the muscarinic receptor antagonist scopolamine on behavioral and electrophysiological measures of contingent attentional capture. The results demonstrated all the signs of functional contingent capture, i.e., attentional shifts toward cued locations reflected in increased amplitudes of N1 and N2Pc components, under placebo conditions. However, scopolamine did not affect behavioral or electrophysiological measures of contingent capture. Instead, scopolamine reduced the amplitude of the distractor-evoked Pd component which has recently been associated with active suppression of irrelevant distractor information. The findings suggest a general cholinergic modulation of top-down control during distractor processing.

(Invited) Plasmonic Driving of Chemical Reactions

Noble metal nanocrystals, possessing localized surface plasmon resonance, can interact strongly with light, efficiently converting light into heat and generating hot electrons and hot holes. Both plasmonic photothermal conversion and generation of hot charge carriers can accelerate chemical reactions. While the acceleration of chemical reactions by photothermal conversion is straightforward, the driving and acceleration of chemical reactions by plasmonic hot charge carriers represents a new research field. Plasmonic hot charge carriers can not only enhance the reaction yield and selectivity, but also introduce new reaction pathways. A full understanding of the latter process requires the knowledge of localized plasmon, electron/hole dynamics, charge transfer, and electron/hole-induced reactions. The study of plasmonic driving of chemical reactions will be rewarding in both fundamental and technological aspects.The lifetime of plasmonic hot charge carriers is on the femtosecond scale. Without utilization, they will rapidly relax, converting their energy into heat. Two approaches have mainly been developed to facilitate the utilization of plasmonic hot charge carriers. The first is the integration of Au or Ag nanocrystals with Pd or Pt nanoparticles. Au and Ag nanocrystals possess strong localized plasmon resonance, while Pd and Pt nanoparticles are excellent catalysts for a variety of chemical reactions. A combination of the two types of metal nanocrystals can lead to efficient light absorption and generation of plasmonic hot charge carriers, which can subsequently inject into molecules that are adsorbed on the Pd or Pt component. The second is the integration of plasmonic metals with semiconductors. A barrier is formed at the interface. The generated hot electrons and holes can quickly inject into the conduction or valence band and therefore get separated. The injected charge carriers can then drive chemical reactions. We have synthesized bimetallic nanocrystals as well as metal/semiconductor hybrid nanostructures to demonstrate plasmonic driving of chemical reactions by both approaches.

Suppression of irrelevant information from working memory is reflected in the PD and CDAp components of the EEG

Suppression of irrelevant information from working memory is reflected in the PD and CDAp components of the EEG

Salient-but-irrelevant stimuli cause attentional capture in difficult, but attentional suppression in easy visual search.

Search for a shape target is difficult when its shape is similar to the shape of the surrounding nontargets and easy when it is dissimilar. We asked whether interference from a salient but irrelevant color singleton depended on search difficulty as manipulated by target-nontarget similarity. We found that interference was strong in difficult searches, and the occurrence of an electrophysiological index of attentional selectivity (the N2pc component) confirmed that attention was captured by the distractor. In contrast, interference from the distractor was weak with easy searches, and the occurrence of the PD component confirmed that saliency signals from the distractor were suppressed. The results suggest that attentional suppression of salient but irrelevant distractors is only possible when search is efficient (i.e., with low target-nontarget similarity), otherwise, attentional capture occurs. Further, we analyzed the Ppc component, a positivity occurring between 100 and 200 ms after stimulus onset contralateral to a salient feature discontinuity. It has been suggested that the Ppc reflects bottom-up saliency signals, but we found the Ppc to occur only when the salient stimulus was unlikely to be selected, as in efficient searches. Thus, attentional requirements modulate the Ppc component.

The different roles of category- and feature-specific attentional control settings on attentional enhancement and inhibition.

Contingent attentional capture suggests that top-down attentional control settings (ACS) can enhance attentional processing of task-relevant properties and inhibit attentional processing of task-irrelevant properties. However, it remains unclear how ACS operates when a distractor has both task-relevant and task-irrelevant characteristics. In the present study, two lateralized ERP components, N2pc and distractor positivity (Pd), were employed as markers of attentional enhancement and inhibition, respectively. The degree of matching between a distractor and a conjunctively defined target was manipulated to illustrate attentional guidance by category-specific ACS (cACS) and feature-specific ACS (fACS), and the relative position between the distractor and the target was manipulated to isolate the processing of the distractor and the target. Experiment 1 showed that, with a long display duration for searching, a reliable N2pc component was elicited by a distractor that was feature-matched but category-mismatched (C-F+) relative to the target-defined properties, suggesting an enhancing effect of fACS. In contrast, Experiment 2 demonstrated that, with a short display duration, a Pd component was elicited by a distractor that was feature-mismatched but category-matched (C+F-) relative to the target-defined properties, suggesting an inhibitory effect of fACS. Moreover, both attentional enhancement and inhibition were only triggered by fACS but not by cACS. In summary, ACS can enhance target-relevant properties or inhibit target-irrelevant properties in response to the display duration, and fACS affects both enhancement and inhibition more than cACS.

New and unusual Pd-Tl-bearing mineralization in the Anomal'nyi deposit, Kondyor concentrically zoned complex, northern Khabarovskiy kray, Russia

AbstractNew Pd-Tl-(Bi,As)-rich compounds are described from the Anomal'nyi Cu-PGE deposit, Kondyor alkaline ultramafic complex, northeastern Russia. They occur in vein-type settings associated with bodies of 'kosvite' (magnetite-rich clinopyroxenite) in the dunite-(peridotite) core, in pegmatiticand micaceous rocks. The ore zones are substantially enriched in phlogopite; they consist of diopside, disseminated titaniferous magnetite and fluorapatite (Sr-bearing). The observed assemblages of ore minerals include sulfides of the chalcopyrite-bornite-(secondary chalcocite) associationand various species of platinum-group minerals (PGM) [isomertieite or arsenopalladinite rich in Sb, mertieite-II, mertieite-I, sobolevskite, kotulskite, merenskyite, zvyagintsevite, palarstanide, paolovite, sperrylite, maslovite or moncheite, hollingworthite and unnamed species of PGM] anda Ag-Au alloy. The oxides [Pd4(Bi,Te,Tl)O6 and Pd4(Tl,Bi,Te)O6] probably formed in situ by oxidation reactions at the expense of the associated PGM intergrowths. These involve palladium bismuthide-thallide phases, Pd5(Tl,As,Bi)and Pd5(As,Tl,Bi), which are documented here for the first time. A fairly evolved environment, enriched in Cu, Pd, Te, Bi, Pb and volatile components, is indicated for the vein-type deposit at Anomal'nyi.

Enhanced Thermal Stability of Pd/Ce–Sn–O Catalysts for CO Oxidation Prepared by Plasma-Arc Synthesis

The plasma-arc (PA) method was applied for the highly efficient synthesis of Pd/Ce–Sn–O catalysts for CO oxidation. Using the PA sputtering of a graphite electrode together with Pd, Ce and Sn metallic components in inert atmosphere, a PdCeSnC composite was obtained. After the subsequent calcination in oxygen over the temperature range of 600–1000 °C, the initial composites were transformed into active catalysts of CO oxidation at low temperatures (LTO CO). Catalytic testing showed that these PA-prepared Pd/Ce–Sn–O catalysts were characterized by unusually high thermal stability. The catalysts demonstrated the excellent LTO CO performance after calcination at 1000 °C. According to the XRD and HRTEM observations, the Pd/Ce–Sn–O catalysts can be described as heterogeneous structures consisting of small CeO2 and SnO2 particles that interact with each other, forming extended grain boundaries and a composite structure. The TPR-CO and XPS methods detected highly dispersed Pd species in the active catalysts, namely Pd2+ in the lattice of ceria (a Pd-ceria solid solution) and the PdOx clusters on the surface. Deactivation of the Pd/Ce–Sn–O is governed by decomposition of the Pd-ceria solid solution accompanied by the sintering of the PdOx clusters and formation of the metallic and oxide palladium nanoparticles. Oxygen species with high mobility in the Pd/Ce–Sn–O catalyst were detected by a TPR-CO method. The amount of the highly mobile oxygen species is in five times higher for the Pd/Ce–Sn–O catalyst then for the Pd/CeO2 sample. Promising perspectives of the plasma-arc application for catalyst the synthesis of with improved properties are discussed.