Recovery of Platinum and Palladium from Spent Automotive Catalysts: Study of a New Leaching System Using a Complete Factorial Design

The recovery of materials and energy from end-of-life products is increasingly a fundamental factor in the sustainable development of various countries. Recovering metals from different types of waste is not only a practice in support of the environment, but is also a profitable economic activity. For this reason, exhausted automotive catalysts can become renewable sources of critical raw materials such as Pt, Pd, and Rh. However, recovering Pt and Pd from spent catalysts through an efficient, economical, and green method remains a challenge. This article presents a new leaching process for the hydrometallurgical recovery of Pt and Pd from exhausted automotive catalysts. The leaching solution consists of an aqueous mixture of hydrochloric acid, two organic acids (citric acid and acetic acid) and hydrogen peroxide. A complete factorial plan on two levels (2k) was performed in order to evaluate the main effects of the analyzed factors and their interactions. The factors that were presumed to be the most influential on the leaching of Pt and Pd were the concentrations of the different reagents and the reaction time. The optimal circumstances for achieving the largest recovery (over 80% Pt and 100% Pd) were achieved using the following conditions: a concentration of HCl of 5 M, a concentration of H2O2 of 10% wt./vol., a concentration of C2H4O2 of 10%vol./vol., and a reaction time of 3 h.

News-based uncertainty measures and returns on prices of precious metals: evidence from regime switching and time-varying causality approach

PurposeThe study aims to examine the relationship among economic policy uncertainty (EPU), geopolitical-risks (GPR), the interaction (EPGR) of EPU and GPR and the returns of gold, silver, platinum, palladium and rhodium using monthly data from January (1997) to May (2021).Design/methodology/approachThe paper employs the Markov-switching and the novel Shi et al. (2020) bootstrap time-varying Granger-causality approach.FindingsThough the Markov-switching shows variation in the responses of precious metals to EPU, GPR and EPGR across low and high states, the paper observes the safe-haven potential of the precious metals in the high regime while the hedging potency is also evident in the results. To further substantiate the safe-haven and hedging properties, the time-varying Granger-causality shows the causal effect of EPU on all the selected precious metal returns coinciding with global events. While the authors show that GPR Granger causes platinum, palladium and rhodium consistently under the rolling/recursive-evolving tests, the authors cannot find the causal effect of GPR on gold and silver returns across the algorithms. The paper also observes persistence in the causal effect of EPGR on palladium and platinum across all the algorithms, while gold and rhodium only show consistency in the responses under the rolling- and recursive-evolving algorithms given the conditions of homoscedasticity and heteroscedasticity.Practical implicationsThe authors' results are essential to investors and policymakers since both typically leverage the hedging and safe-haven characteristics of precious metals to obviate downside risks during highly uncertain periods.Originality/valueThe authors' techniques allow examining the hedging and safe-haven properties of precious metals across regimes and date-stamp critical periods of causation inherent in the relationship.

Forecasting the volatility of precious metals prices with global economic policy uncertainty in pre and during the COVID-19 period: Novel evidence from the GARCH-MIDAS approach

Economic policy is a major determinant of investment and financial decisions;Moreover, prices of precious metals are highly influenced by any uncertainty recorded in the global economic policy. Therefore, the prime consideration of the authors is to assess how global economic policy uncertainty influences the volatility of precious metals prices;particularly "gold, palladium, platinum, and silver” in the pre and during the COVID-19 pandemic. This research analyzed the full sample period (the 1997–2022), pre-COVID period (1997–2019), and during the COVID period (2020−2022) to evaluate the impact during different sample periods. Therefore, the GARCH-MIDAS approach is employed at the data set of different frequencies, i.e., monthly data of GEPU and daily data of precious metals. The results reveal a significant nexus between global GEPU and precious metals price volatility. The findings infer that any uncertainty recorded in global economic policy escalate the price volatility of gold, palladium, platinum, and silver prices. The present study increments the existing literature and provides insights for future scholars, investors, and policymakers. © 2023 Elsevier B.V.

Electrocatalytic Palladium Nanoclusters as Versatile Indicators of Bioassays: Rapid Electroanalytical Detection of SARS-CoV-2 by Reverse Transcription Loop-Mediated Isothermal Amplification.

Quantitative polymerase chain reaction (qPCR) is considered the gold standard for pathogen detection. However, improvement is still required, especially regarding the possibilities of decentralization. Apart from other reasons, infectious diseases demand on-site analysis to avoid pathogen spreading and increase treatment efficacy. In this paper, the detection of SARS-CoV-2 is carried out by reverse transcription loop-mediated isothermal amplification, which has the advantage of requiring simple equipment, easily adaptable to decentralized analysis. It is proposed, for the first time, the use of palladium nanoclusters (PdNCs) as indicators of the amplification reaction at end point. The pH of the medium decreases during the reaction and, in turn, a variation in the catalytic activity of PdNCs on the oxygen reduction reaction (ORR) can be electrochemically observed. For the detection, flexible and small-size screen-printed electrodes can be premodified with PdNCs, which together with the use of a simple and small electrochemical equipment would greatly facilitates their integration in field-deployable devices. This would allow a faster detection of SARS-CoV-2 as well as of other future microbial threats after an easy adaptation.

Biogenic metal nanomaterials to combat antimicrobial resistance

Antimicrobial resistance is one of the biggest problems that the healthcare system faces nowadays, with an increasing burden due to the COVID-19 pandemic. Different alternatives to the current treatments of bacterial infections have been studied far away from the use of traditional antibiotics. One of them is nanotechnology, which proposes a suitable solution without the associated problems. Still, the production of different nanomaterials often shows disadvantages, such as producing toxic by-products or the need for functionalization to deliver a suitable therapeutic effect. The implementation of green nanotechnology in nanomaterials synthesis shows great potential, with specific implementation in metal-based nanomaterials. As such, this chapter revised the state of biogenic or biologically produced metal nanoparticles produced by bacteria, fungi, and plant extracts with antimicrobial applications against antibiotic-resistant strains. The chapter summarizes and discusses some of the newest advances in the field to demonstrate that these nanostructures can become a significant enhancement in the fight towards superbugs. © 2022 Elsevier Inc. All rights reserved.

Metallic natural resources commodity prices volatility in the pandemic: Evidence for silver, platinum, and palladium

The current study investigates volatility in natural resource commodity prices in the case of the US. Particularly, this study focused on the rarely explained indicators of natural resources, including palladium, platinum, and silver price volatility, from February 28, 2012, to March 18, 2020. Since the Covid-19 pandemic creates havoc in the global economic system, that creates uncertainty in the natural resources market. Therefore, the period of the Covid-19 pandemic is also considered in the empirical investigation. This study uses the traditional autoregressive conditional heteroscedasticity (ARCH) approach, which reveals that the ARCH effect is valid in the mentioned variables in both the pre and post Covid-19 pandemic periods. Besides, this study also employed the threshold generalized autoregressive conditional heteroscedasticity (TGARCH) and exponential generalized autoregressive conditional heteroscedasticity (EGARCH) models to analyze shock asymmetry. The estimated outcomes asserted that platinum and silver prices are more sensitive to negative shocks such as the Covid-19 pandemic. However, positive shocks play a more influential role in palladium price volatility. Thus, the shock asymmetry is valid for all three metallic resources. Based on the empirical findings, this study suggests implementing price ceiling policies. Besides, metallic resources hedging and the imposition of strong regulations in the financial market could help reduce volatility in natural resources.

Advances in Synthetic Strategies and Medicinal Importance of Benzofurans: A Review

Out of the many heterocycles that exhibit pharmaceutical and therapeutic properties, benzofurans remain the most eye-catching to scientists ever since their discovery. From being present in natural products to synthetic analogs they show diverse biological properties which are used to treat various diseases. Interestingly, some of the benzofuran hybrids were docked against COVID-19 Main Protease and it showed appealing results. Apart from medicinal properties it also exhibits some non-drug applications. The structure activity relationship of benzofuran derivatives in many infections draws attention to the extent where drugs can be produced in a short time span which highlights their significance in medicinal chemistry. There are considerable reaction schemes to synthesize this moiety either simple one pot reactions or multistep. Here, we emphasize on the chemistry of benzofurans, synthesis and its derivatives in the recent years, some of which show notable anti-tumor, anti-fungal, anti-mycobacterial and anti-oxidant activities.

The dual therapeutic effect of metformin nuclei-based drugs modified with one of Tulbaghia violacea extract compounds

Novel Schiff base was synthesized from the condensation reaction of metformin with [4-(Diethylamino) benzaldehyde (NBM). Different metal complexes were prepared using Pd (II), Pt (II), Cu (II), and V (IV) metal ions. All complexes showed the nonelectrolytic behavior. So, the expected molecular formulas for complexes were [Pd (NBM)Cl2], [Pt (NBM)Cl2], [Cu (NBM)2Cl2] and [VO (NBM)2]. The cytotoxicity of (NBM) Schiff base and its metal complexes on human cancer cell line, MCF-7, was investigated. V (IV) and Cu (II) complexes showed potential blood glucose lowering effect higher than the commercial metformin drug. VO (II) complex has superior antioxidant activity more than the other synthesized compounds and the standard ascorbic acid. Molecular docking investigation proved the presence of interesting interactions between all synthesized compounds with the active site amino acids of EGFR tyrosine kinase (anticancer activity). The molecular docking of metal complexes has observed effective inhibition for the specific mTOR protein that is expected to aid the growth of the COVID-19 virus. © 2022 John Wiley & Sons, Ltd.

On the stylized facts of precious metals’ volatility: A comparative analysis of pre- and during COVID-19 crisis

The main aim of this paper is to investigate the stylized facts associated with the volatility of precious metals before and during the COVID-19 pandemic using GARCH-type models. In particular, we employ an ARMA-GARCH, ARMA-EGARCH and ARMA-FIGARCH framework to account for volatility clustering, asymmetry and long memory in the volatility of gold, silver, platinum and palladium. Based on structural breaks, we divide the whole sample into sub-samples and find that the breakpoints occurred after the declaration of COVID-19 pandemic. Our results show a very distinct behaviour in the memory of the four metals before and during the crisis. While there is a moderate persistence in the full sample and in the pre-COVID-19 sub-period for the four metals, this effect vanishes after the crisis outburst. Positive asymmetric effects are also found in gold and silver volatilities, which intensify during COVID-19 phase. We ascribe this phenomenon to the hedge/safe-haven properties of these metals. By contrast, a diverse pattern is observed in the palladium and platinum volatilities, which display negative asymmetries before the pandemic, in tandem of financial markets. After the crisis, these metals show mixed evidence. Moreover, we argue that COVID-19 significantly affects the volatility of precious metals. © 2022 Elsevier B.V.

Functionalization of Porphyrins Using Metal-Catalyzed C–H Activation

The review is devoted to the C–H functionalization of porphyrins. Porphyrins exhibit the properties of organic semiconductors, light energy converters, chemical and electrochemical catalysts, and photocatalysts. The review describes the iridium- and palladium-catalyzed direct functionalization of porphyrins, with more attention given to the results obtained in our laboratory. The development and improvement of synthetic methods that do not require preliminary modification of the substrate with various functional groups are extremely important for the preparation of new organic materials based on porphyrins. This makes it possible to simplify the synthetic procedure, to make the synthesis more economical, environmentally safe, and simple to perform.

Evaluation of a photoelectrochemical platform based on strontium titanate, sulfur doped carbon nitride and palladium nanoparticles for detection of SARS-CoV-2 spike glycoprotein S1.

This work aims to develop a photoelectrochemical (PEC) platform for detection of SARS-CoV-2 spike glyprotein S1. The PEC platform is based on the modification of a fluorine-doped tin oxide (FTO) coated glass slide with strontium titanate (SrTiO3 or ST), sulfur-doped carbon nitride (g-C3N4-S or CNS) and palladium nanoparticles entrapped in aluminum hydroxide matrix (PdAlO(OH) or PdNPs). The PEC platform was denoted as PdNPs/CNS/ST/FTO and it was characterized by SEM, TEM, FTIR, DRX, and EIS. The PEC response of the PdNPs/CNS/ST/FTO platform was optimized by evaluating the effects of the concentration of the donor molecule, the nature of the buffer, pH, antibody concentration, potential applied to the working electrode, and incubation time. The optimized PdNPs/CNS/ST/FTO PEC platform was modified with 5 µg mL-1 of antibody for determination of SARS-CoV-2 spike glycoprotein S1. A decrease in the photocurrent was observed with an increase in the concentration of SARS-CoV-2 from 1 fg mL-1 to 1000 pg mL-1 showing that the platform is a promising alternative for the detection of S1 protein from SARS-CoV-2. The designed PEC platform exhibited recovery percentages of 96.20% and 109.65% in artificial saliva samples.

Performance of Pd catalyst supported on trimetallic nanohybrid Zr–Al–La in hydrogenation of ethylanthraquinone

In light of the recent COVID-19 pandemic, the demand for hydrogen peroxide has increased significantly due to its widespread use in disinfectant formulations. The present study aims to develop an efficient nanohybrid material as catalyst support for the successful hydrogenation of ethylanthraquinone for the production of hydrogen peroxide. Co-precipitation and wet impregnation methods were used to prepare nanohybrid Zr–Al–La supported Pd catalyst (Pd/Zr–Al–La). The high surface area (146.56 m2/g) of Zr–Al–La makes it suitable to use as support and causes to lower the mass transfer resistance and dispersion of active metal. XRF, BET, FTIR, and TGA were used to characterize the developed catalyst. The catalytic activity of the developed catalyst was studied using a high-pressure autoclave reactor to obtain a notable yield of H2O2 as 93.8% at 75 °C, 0.3 MPa, and 0.5 g of catalyst dose, a significant enhancement over the traditional Pd catalyst with Al2O3 support (63%) with the loss of active quinone compound. The mass transfer limitation of the reaction is high using only a Pd catalyst. The calculated mass transfer resistance of the reaction over Pd/Zr–Al–La catalyst was found to be moderate with a diffusion coefficient of the reactant (H2) as 0.0133 × 10−6 m2/s at 75 °C. It was also verified and confirmed with the Thiele modulus (calculated as 0.0314), no mass transfer resistance. The effectiveness factor (η s ) was found to be 1.0, indicating the negligible mass transfer resistance in the hydrogenation reaction using Pd/Zr–Al–La catalyst. [ FROM AUTHOR] Copyright of International Journal of Chemical Reactor Engineering is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)

A Review of Recovery of Palladium from the Spent Automobile Catalysts

The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.

Pt-, Rh-, Ru-, and Cu-Single-Wall Carbon Nanotubes Are Exceptional Candidates for Design of Anti-Viral Surfaces: A Theoretical Study.

As SARS-CoV-2 is spreading rapidly around the globe, adopting proper actions for confronting and protecting against this virus is an essential and unmet task. Reactive oxygen species (ROS) promoting molecules such as peroxides are detrimental to many viruses, including coronaviruses. In this paper, metal decorated single-wall carbon nanotubes (SWCNTs) were evaluated for hydrogen peroxide (H2O2) adsorption for potential use for designing viral inactivation surfaces. We employed first-principles methods based on the density functional theory (DFT) to investigate the capture of an individual H2O2 molecule on pristine and metal (Pt, Pd, Ni, Cu, Rh, or Ru) decorated SWCNTs. Although the single H2O2 molecule is weakly physisorbed on pristine SWCNT, a significant improvement on its adsorption energy was found by utilizing metal functionalized SWCNT as the adsorbent. It was revealed that Rh-SWCNT and Ru-SWCNT systems demonstrate outstanding performance for H2O2 adsorption. Furthermore, we discovered through calculations that Pt- and Cu-decorated SWNCT-H2O2 systems show high potential for filters for virus removal and inactivation with a very long shelf-life (2.2 × 1012 and 1.9 × 108 years, respectively). The strong adsorption of metal decorated SWCNTs and the long shelf-life of these nanomaterials suggest they are exceptional candidates for designing personal protection equipment against viruses.

Development of flexible electrochemical impedance spectroscopy-based biosensing platform for rapid screening of SARS-CoV-2 inhibitors.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the cells through the binding of its spike protein (S-protein) to the cell surface-expressing angiotensin-converting enzyme 2 (ACE2). Thus, inhibition of S-protein-ACE2 binding may impede SARS-CoV-2 cell entry and attenuate the progression of Coronavirus disease 2019 (COVID-19). In this study, an electrochemical impedance spectroscopy-based biosensing platform consisting of a recombinant ACE2-coated palladium nano-thin-film electrode as the core sensing element was fabricated for the screening of potential inhibitors against S-protein-ACE2 binding. The platform could detect interference of small analytes against S-protein-ACE2 binding at low analyte concentration and small volume (0.1 µg/mL and ~1 µL, estimated total analyte consumption < 4 pg) within 21 min. Thus, a few potential inhibitors of S-protein-ACE2 binding were identified. This includes (2S,3aS,6aS)-1-((S)-N-((S)-1-Carboxy-3-phenylpropyl)alanyl)tetrahydrocyclopenta[b] pyrrole-2-carboxylic acid (ramiprilat) and (2S,3aS,7aS)-1-[(2S)-2-[[(2S)-1-Carboxybutyl]amino]propanoyl]-2,3,3a,4,5,6,7,7a-octahydroindole-2-carboxylic acid (perindoprilat) that reduced the binding affinity of S-protein to ACE2 by 72% and 67%; and SARS-CoV-2 in vitro infectivity to the ACE2-expressing human oral cavity squamous carcinoma cells (OEC-M1) by 36.4 and 20.1%, respectively, compared to the PBS control. These findings demonstrated the usefulness of the developed biosensing platform for the rapid screening of modulators for S-protein-ACE2 binding.

Stable dechlorination of Trichloroacetic Acid (TCAA) to acetic acid catalyzed by palladium nanoparticles deposited on H2-transfer membranes.

Trichloroacetic acid (TCAA) is a common disinfection byproduct (DBP) produced during chlorine disinfection. With the outbreak of the Coronavirus Disease 2019 (COVID-19) pandemic, the use of chlorine disinfection has increased, raising the already substantial risks of DBP exposure. While a number of methods are able to remove TCAA, their application for continuous treatment is limited due to their complexity and expensive or hazardous inputs. We investigated a novel system that employs palladium (Pd0) nanoparticles (PdNPs) for catalytic reductive dechlorination of TCAA. H2 was delivered directly to PdNPs in situ coated on the surface of bubble-free hollow-fiber gas-transfer membranes. The H2-based membrane Pd film reactor (H2-MPfR) achieved a high catalyst-specific TCAA reduction rate, 32 L/g-Pd/min, a value similar to the rate of using homogeneously suspended PdNP, but orders of magnitude higher than with other immobilized PdNP systems. In batch tests, over 99% removal of 1 mM TCAA was achieved in 180 min with strong product selectivity (≥ 93%) to acetic acid. During 50 days of continuous operation, over 99% of 1 mg/L influent TCAA was removed, again with acetic acid as the major product (≥ 94%). We identified the reaction pathways and their kinetics for TCAA reductive dechlorination with PdNPs using direct delivery of H2. Sustained continuous TCAA removal, high selectivity to acetic acid, and minimal loss of PdNPs support that the H2-MPfR is a promising catalytic reactor to remove chlorinated DBPs in practice.