This review covers the structure of, and chemical reactions on, well-defined cerium oxide surfaces. Ceria, or mixed oxides containing ceria, are critical components in automotive three-way catalysts ...due to their well-known oxygen storage capacity. Ceria is also emerging as an important material in a number of other catalytic processes, particularly those involving organic oxygenates and the water–gas shift reaction. Ceria׳s acid–base properties, and thus its catalytic behavior, are closely related to its surface structure where different oxygen anion and cerium cation environments are present on the low-index structural faces. The actual structure of these various faces has been the focus of a number of theoretical and experimental investigations. Ceria is also easily reducible from CeO2 to CeO2−X. The presence of oxygen vacancies on the surface often dramatically alters the adsorption and subsequent reactions of various adsorbates, either on a clean surface or on metal particles supported on the surface. Most surface science studies have been conducted on the surfaces of thin-films rather than on the surfaces of bulk single crystal oxides. The growth, characterization and properties of these thin-films are also examined.
Although there are only a few known examples of supported single-atom catalysts, they are unique because they bridge the gap between homogeneous and heterogeneous catalysis. Here, we report the CO ...oxidation activity of monodisperse single Pt atoms supported on an inert substrate, θ-alumina (Al2O3), in the presence of stoichiometric oxygen. Since CO oxidation on single Pt atoms cannot occur via a conventional Langmuir–Hinshelwood scheme (L–H scheme) which requires at least one Pt–Pt bond, we carried out a first-principles density functional theoretical study of a proposed pathway which is a variation on the conventional L–H scheme and inspired by the organometallic chemistry of platinum. We find that a single supported Pt atom prefers to bond to O2 over CO. CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO2, leaving an oxygen atom on Pt. Subsequent reaction with another CO molecule regenerates the single-atom catalyst. The energetics of the proposed mechanism suggests that the single Pt atoms will get covered with CO3 unless the temperature is raised to eliminate CO2. We find evidence for CO3 coverage at room temperature supporting the proposed mechanism in an in situ diffuse reflectance infrared study of CO adsorption on the catalyst’s supported single atoms. Thus, our results clearly show that supported Pt single atoms are catalytically active and that this catalytic activity can occur without involving the substrate. Characterization by electron microscopy and X-ray absorption studies of the monodisperse Pt/θ-Al2O3 are also presented.
The surface chemistry and catalytic activity of small alcohols (methanol, ethanol, and propan-2-ol) were studied over LaMnO3(100) and La0.7Sr0.3MnO3(100) thin films. The observed C-containing ...products corresponded to products typically associated with dehydrogenation (methanal, ethanal, and propanone), dehydration (ethene and propene), and oxidation (CO x ). No coupling products were observed. Two types of temperature-programmed reaction experiments (TPR) were performed: pre-exposure TPR (PE-TPR) experiments in which the reactant is preadsorbed and the temperature is then ramped, as well as continuous exposure TPR (CE-TPR) experiments during which the reactants are continuously introduced and the temperature is ramped. Mechanistic pathways are proposed based on the results and literature, including removal of lattice oxygens by surface hydrogens, organic intermediates adsorbed in oxygen vacancies, C–H bond breaking by alkoxy disproportionation reactions, and direct C–H bond breaking. The vacancy related pathways are suppressed by the Sr substitution. The data are interpreted to indicate that Sr substitution causes vacancies to bind adsorbates less strongly, resulting in decreased catalytic activity for the vacancy-mediated reactions in the study. Sr substitution increases the ratio of alkene production to aldehyde/ketone production. Catalytic turnover frequencies are reported for the C-containing products for the temperatures of 650 and 750 K for both surfaces.
The measurement of volumetric titer is an integral step in the assessment and selection of a production cell line and cell culture process. The production of monoclonal antibodies (mAbs), a major ...class of therapeutic proteins, in Chinese Hamster Ovary (CHO) cell lines is challenging due to the clone-to-clone variations in the intrinsic capability to secrete a biologically complex protein. The measurement of intracellular mAb concentration could be a valuable tool to determine the ratio of intracellular to secreted product and be part of the evaluation of potential mAb productive cell lines. High throughput automation is a valuable tool that is used in bioprocess development to reduce work intensive steps. When coupled with the Simple Western (Wes) platform, automated capillary electrophoresis is an efficient method to measure recombinant protein concentration. In this study, we demonstrate the utility of using the automated Wes to rapidly measure intracellular titer and then compare the intracellular titer, volumetric titer and specific productivity between high and low production CHO clones expressing a model human IgG1 mAb.
•Capillary electrophoresis can be used to develop a standard curve to quantitatively measure protein.•Intracellular recombinant protein can be quantitatively measured with capillary electrophoresis.•There are observable differences in the intracellular titer between high- and low-production CHO clone.•Intracellular and volumetric titers are correlated between high- and low-production CHO clones.
Although cardiac magnetic resonance (CMR) and positron emission tomography (PET) detect different pathological attributes of cardiac sarcoidosis (CS), the complementary value of these tests has not ...been evaluated. Our objective was to determine the value of combining CMR and PET in assessing the likelihood of CS and guiding patient management.
In this retrospective study, we included 107 consecutive patients referred for evaluation of CS by both CMR and PET. Two experienced readers blinded to all clinical data reviewed CMR and PET images and categorized the likelihood of CS as no (<10%), possible (10%-50%), probable (50%-90%), or highly probable(>90%) based on predefined criteria. Patient management after imaging was assessed for all patients and across categories of increasing CS likelihood. A final clinical diagnosis for each patient was assigned based on a subsequent review of all available imaging, clinical, and pathological data. Among 107 patients (age, 55±11 years; left ventricular ejection fraction, 43±16%), 91 (85%) had late gadolinium enhancement, whereas 82 (76%) had abnormal F18-fluorodeoxyglucose uptake on PET, suggesting active inflammation. Among the 91 patients with positive late gadolinium enhancement, 60 (66%) had abnormal F18-fluorodeoxyglucose uptake. When PET data were added to CMR, 48 (45%) patients were reclassified as having a higher or lower likelihood of CS, most of them (80%) being correctly reclassified when compared with the final diagnosis. Changes in immunosuppressive therapies were significantly more likely among patients with highly probable CS.
Among patients with suspected CS, combining CMR and PET provides complementary value for estimating the likelihood of CS and guiding patient management.
This study reports and compares the adsorption and dissociation of water on oxidized and reduced CeO2(100) and CeO2(111) thin films. Water adsorbs dissociatively on both surfaces. On fully oxidized ...CeO2(100) the resulting surface hydroxyls are relatively stable and recombine and desorb as water over a range from 200 to 600 K. The hydroxyls are much less stable on oxidized CeO2(111), recombining and desorbing between 200 and 300 K. Water produces 30% more hydroxyls on reduced CeO1.7(100) than on oxidized CeO2(100). The hydroxyl concentration increases by 160% on reduced CeO1.7(111) compared to oxidized CeO2(111). On reduced CeO1.7(100) most of the hydroxyls still recombine and desorb as water between 200 and 750 K. Most of the hydroxyls on reduced CeO1.7(111) react to produce H2 at 560 K, leaving O on the surface. A relatively small amount of H2 is produced from reduced CeO1.7(100) between 450 and 730 K. The differences in the adsorption and reaction of water on CeO X (100) and CeO X (111) are attributed to different adsorption sites on the two surfaces. The adsorption site on CeO2(100) is a bridging site between two Ce cations. This adsorption site does not change when the ceria is reduced. The adsorption site on CeO2(111) is atop a single Ce cation, and the proton is transferred to a surface O in a site between three Ce cations. When the CeO X (111) is reduced, vacancy sites are produced which allows the water to adsorb and dissociate on the 3-fold Ce cation sites.
The reactions of methanol with and without O2 were studied on a flat, highly crystalline CeO2(100) thin‐film surface with ambient pressure XPS. In the absence of O2, the ambient pressure XPS results ...indicate that in both low‐pressure (≤10−5 Torr) and high‐pressure regimes (≥10−1 Torr), the dominant surface species is methoxy. Methanol decomposition substantially reduces the ceria and CX deposit build‐up on the surface. When O2 is present, CX does not accumulate on the surface and the dominant surface species is different in the low‐pressure and high‐pressure regimes. Methoxy dominates at low pressure, while formate dominates at the higher pressure. The type of surface species appears to be related to the ability of O2 to fully oxidize the ceria surface during the methanol reaction.
Immune checkpoint inhibitor (ICI) therapies represent a major advance in treating a variety of advanced-stage malignancies. Nevertheless, only a subset of patients benefit, even when selected based ...on approved biomarkers such as PD-L1 and tumor mutational burden. New biomarkers are needed to maximize the therapeutic ratio of these therapies.
In this retrospective cohort, we assessed a 27-gene RT-qPCR immuno-oncology (IO) gene expression assay of the tumor immune microenvironment and determined its association with the efficacy of ICI therapy in 67 advanced-stage NSCLC patients. The 27-gene IO test score (IO score), programmed cell death ligand 1 immunohistochemistry tumor proportion score (PD-L1 TPS), and tumor mutational burden (TMB) were analyzed as continuous variables for response and as binary variables for one-year progression free survival. The threshold for the IO score was prospectively set based upon a previously described training cohort. Prognostic implications of the IO score were evaluated in a separate cohort of 104 advanced-stage NSCLC patients from The Cancer Genome Atlas (TCGA) who received non-ICI therapy.
The IO score was significantly different between responders or non-responders (p = 0.007) and associated with progression-free survival (p = 0.001). Bivariate analysis established that the IO score was independent of PD-L1 TPS and TMB in identifying patients benefiting from ICI therapy. In a separate cohort of late-stage NSCLC patients from TCGA, the IO score was not prognostic of outcome from non-ICI-treated patients.
This study is the first application of this 27-gene IO RT-qPCR assay in a clinical cohort with outcome data. IO scores were significantly associated with response to ICI therapy and prolonged progression-free survival. Together, these data suggest the IO score should be further studied to define its role in informing clinical decision-making for ICI treatment in NSCLC.
Methanol has been considered as a “smart” molecule in studying the surface sites of metal oxide catalysts. In this work, methanol was utilized to probe the nature of surface sites of ceria ...nanocrystals with defined surface planes (nanoshapes), including rods (containing {110}), cubes ({100}), and octahedra ({111}). The adsorption and desorption of methanol were followed by in situ IR and Raman spectroscopy as well as mass spectrometry. Upon methanol adsorption at room temperature, on-top, bridging and three-coordinate methoxy species are formed on the surface of rods and cubes, whereas only on-top methoxy is present on the octahedra surface. The distribution of the methoxy species is believed to be determined not only by the coordination status of surface Ce cations but also by the number of defect sites on the three nanoshapes. During the desorption process, the methoxy species are gradually dehydrogenated into H2 and CO via formate species as intermediates on the three ceria surfaces. A second intermediate, formyl species is also evident on the rods’ surface. The methoxy species are more reactive and less stable on the rods’ surface, which results in desorption of H2 and CO at lower temperature (<583 K) than on cubes and octahedra. A higher than stoichiometric H/CO ratio is observed in the methanol-TPD products, attributed to the retention of some amount of formate and carbonate species on the ceria nanoshapes, as revealed by in situ IR. A small amount of methanol and formaldehyde desorbs at low temperature (<423 K) on the three surfaces as a result of the disproportionation reaction of the methoxy species. The UV Raman and IR results indicate that the ceria nanoshapes are slightly reduced at room temperature upon methanol adsorption and become more reduced at higher temperatures during methanol desorption. The degree of reduction is found to be dependent on the surface structure of the ceria nanoshapes.
The temperature-dependent adsorption and reaction of acetaldehyde (CH3CHO) on a fully oxidized and a highly reduced thin-film CeO2(111) surface have been investigated using a combination of ...reflection–absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde adsorbs weakly through its carbonyl O interacting with a lattice Ce4+ cation in the η1-O configuration. This state desorbs at 210 K without reaction. On the highly reduced surface, new vibrational signatures appear below 220 K. They are identified by RAIRS and DFT as a dimer state formed from the coupling of the carbonyl O and the acyl C of two acetaldehyde molecules. This dimer state remains up to 400 K before decomposing to produce another distinct set of vibrational signatures, which are identified as the enolate form of acetaldehyde (CH2CHO¯). Furthermore, the calculated activation barriers for the coupling of acetaldehyde, the decomposition of the dimer state, and the recombinative desorption of enolate and H as acetaldehyde are in good agreement with previously reported TPD results for acetaldehyde adsorbed on reduced CeO2(111) Chen et al. J. Phys. Chem. C 2011, 115, 3385. The present findings demonstrate that surface oxygen vacancies alter the reactivity of the CeO2(111) surface and play a crucial role in stabilizing and activating acetaldehyde for coupling reactions.
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