H2 CO2 Research Articles

Bimetallic metal-organic frameworks for efficient visible-light-driven photocatalytic CO2 reduction and H2 generation

A series of robust octahedral bimetallic metal-organic frameworks, NH2-UiO-66(Zr/M), denoted as Zr/M-ATA, (where M is Fe, Co, or Cu) were prepared by solvothermal de novo reaction of 2-aminoterephthalic acid (denoted as H2ATA) and mixed metal salts using benzoic acid as a modulator. Photocatalytic studies revealed that Zr/Fe-ATA, Zr/Cu-ATA and Zr/Co-ATA containing double metals outperformed that of the monometallic Zr-ATA. Zr/Cu-ATA displayed excellent performance for visible-light-driven CO2 reduction with a formate formation rate of 122 μmol h−1 mmolMOF-1, which is among the highest performance of NH2-UiO-66 based MOFs. Furthermore, Zr/Cu-ATA is an efficient catalyst that can generate 12.8 mmol of H2 in 2 h under visible light irradiation. The light absorption band of Zr/Cu-ATA shifted to the near-IR region and the presence of Cu-oxo clusters significantly narrowed the bandgap from 2.95 eV (Zr-ATA) to 1.93 eV (Zr/Cu-ATA). Other photoelectrochemical studies further confirmed that the high catalytic performance of Zr/Cu-ATA can be ascribed to optimized bandgap, facile charge transfer and availability of large number of active sites.

High purity hydrogen production via coupling CO2 reforming of biomass-derived gas and chemical looping water splitting

Hydrogen is playing an increasingly larger role in carbon neutrality. However, efficient and sustainable hydrogen production from renewable resources suffers from unwanted side reactions and kinetic inefficiencies. Here, we study a low carbon and renewable H2 production route that integrated biomass-derived gas dry reforming couples chemical looping water splitting process (DR-CLWS). This process requires neither removal of CO2 from upstream biomass-derived gas, nor downstream H2 purification and CO2 separation, hence achieving a great level of process intensification. The reforming temperature, CH4/CO2 ratio, oxygen carrier reduction temperature, reduction behavior, types of fuel gas and oxygen carriers, H2 production, oxygen carrier regeneration and process cyclability were investigated, respectively. The coupling process resulted in higher CH4 conversion (near 100%) and inherently CO2 separation. CO-free H2 was produced due to no carbon being carried over from the reduction cycle to the H2 production cycle. Meanwhile, H2 yields up to 2.93 mmole per mmole CH4. Mass balance analysis reveals that the process can be operated auto-thermal without costly oxygen production or without mixing air with carbon-containing fuel gases. Moreover, the cyclability results showed that the oxygen carrier remained its activity over 265 redox cycles.

Recent Advances on Multivariate MOFs for Photocatalytic CO2 Reduction and H2 Evolution

AbstractSolar energy‐driven CO2 reduction and H2 evolution is considered as a very promising pathway to address energy shortage and environmental issues. Multivariate metal organic frameworks (MTV‐MOFs) as a class of distinctive crystal porous materials are assembled from different metals or different ligands via one pot reaction or postsynthesis approach. Recently, MTV‐MOFs have gathered significantly interest in the field of photocatalytic CO2 reduction and H2 evolution owing to their excellent structural stability, tailorable light‐absorption, and catalytic abilities. In this review, incorporating different functional ligands or metals into the parent MOFs are focused on to boost the photocatalytic performance of MTV‐MOFs. First, the synthesis and unique advantages of MTV‐MOF‐based photocatalysts are introduced. Next, an overview on the recent advance on MTV‐MOFs for solar‐to‐chemical energy conversion is summarized into three main categories, consisting of mixed‐metal MOFs, mixed‐ligand MOFs, and mixed‐metal and mixed‐ligand MOFs. Finally, future perspectives and challenges in CO2 conversion and H2 evolution over MTV‐MOF‐based photocatalysts are presented.

INFLUENCE OF VOLTAGE ON ANODE GAS COMPOSITIONS DURING PLASMA ELECTROLYTIC OXIDATION OF 60 VOL.% SiCp/2009 ALUMINUM MATRIX COMPOSITE

Plasma electrolytic oxidation (PEO) was performed on 60 vol.% SiCp/2009 aluminum matrix composite under different voltages in silicate solution and NaF solution, respectively. Anode gas evolutions under different conditions during the PEO process were evaluated by the gas chromatograph, optical emission spectroscopy, scanning electron microscope, X-ray diffraction and inductively coupled plasma atomic emission spectroscopy. The anode gas released at different voltages in both solutions contained H2, O2 and trace CO. The H2 concentration increased with the increase of voltage in the silicate solution, and then it was kept at 75–80 vol.% in the range from [Formula: see text]480 V/–0 V to [Formula: see text]520 V/–0 V, which was related to the appearance of strong discharge sparks. The H2 concentration of the anode gas in NaF solution was much lower than that in the silicate solution due to the weak discharge. The excessive H2 was caused by nonfaradaic reactions in the plasma discharge region such as thermal decomposition of water. Meanwhile, the O2 in anode gas mainly came from thermal decomposition of water in plasma discharge region and traditional electrochemical reactions in nondischarge region. In addition, SiC reinforcement particles were oxidized in plasma discharge channels with the temperature up to 5000 K, accompanied by the release of trace CO. Furthermore, CO2 was hardly detected due to the effect of H2 reduction in the discharge channels.

REALIZATION OF CONTINIOUSLY ROTATING DETONATION FOR SYNGAS-AIR MIXTURES

Numerical simulation of continuously rotating detonations (CRD) of stoichiometric two-fuel mixture with air has been carried out for the cylindrical annular detonation chamber (DC) of the rocket-type engine. Thesyngas (1 - α)óO + αH2, a binary mixture of hydrogen H2 and carbon monoxide CO, is taken as a fuel. The global flow structure in the DC and the detailed structure of the transverse detonation wave (TDW) front in thecontinuously rotating regime have been studied. Integral characteristics of the detonation process - the distribution of average values of static and total pressure along the length of the DC - and the value of specific impulse on the DC exit have been obtained. The regions of existence of stable CRD regime in coordinates “stagnation pressure pm - stagnation temperature Tm” in the injection manifold (receiver) have been determined. The minimal values of the DC length and radius for CRD for some regions at the pm-Tm plane have been found.

High-Pressure Laminar Flame Speeds and Markstein Lengths of Syngas Flames Diluted in Carbon Dioxide and Helium

Abstract New laminar flame speed and burned-gas Markstein length data for H2–CO–O2–CO2–He mixtures have been measured from spherically expanding flames. Experiments were conducted at 10 atm and room temperature for H2:CO ratios ranging from 2:1 to 1:4 and for overall CO2 mole fractions from 0% to 30%. CO2 dilution had little effect on Markstein length, but CO2 dilutions of 10%, 20%, and 30% caused average reductions in flame speed of 47%, 73%, and 89%, respectively, regardless of H2:CO ratio. The study was designed to isolate the dilution effect of CO2 on flame speed, and a detailed analysis using the FCO2 method was used to show that the chemical-kinetic participation of CO2 was responsible for up to 20% of the reduction in flame speed. Hence, the majority (80% or more) of the reduction in flame speed due to CO2 is from the thermal effect. Accurate flame speed predictions were produced by five different chemical kinetics mechanisms for most conditions, with the slight exception of high-CO, high-CO2 mixtures. A thorough sensitivity analysis highlighted the larger effect of CO2 dilution on the important kinetics reactions than the effect of changing H2:CO. Sensitivity analysis also showed that the chain branching reaction H2O + O ⇌ OH + OH could be modified (albeit beyond its uncertainty) to achieve more accurate flame speed predictions, but also indicated that further improvement of flame speed modeling would require changes to many lesser reactions.

Insights into the Ultrafast Photodissociation Dynamics of Isoprene-Derived Criegee Intermediates.

Isoprene is the most abundant nonmethane volatile organic compound emitted into the troposphere by terrestrial vegetation. Reaction with ozone represents an important isoprene removal process from the troposphere and is a well-known source of Criegee intermediates (CIs), which are reactive carbonyl oxides. Three CIs, formaldehyde oxide (CH2 OO), methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide) are formed during isoprene ozonolysis. All three CIs contain strongly absorbing ππ* states, electronic excitation, which leads to dissociation to form aldehyde/ketone + oxygen products. Here, we compare the excited state chemistry of CH2 OO, MVK-oxide and MACR-oxide in order to ascertain how increasing molecular complexity affects their photodynamics. In CH2 OO, vertical excitation to the S2 state leads to prompt O-O bond fission with a unity quantum yield. Branching into both the O(1 D) + H2 CO (S0 ) and O (3 P) + H2 CO (T1 ) product channels is predicted, with 80% of trajectories dissociating to form the former product pair. Analogous vertical excitation of the lowest energy conformers of MVK-oxide and MACR-oxide also undergoes O-O bond fission to form O + MVK/MACR products-albeit with a nonunity quantum yield. In the latter case, ca. 10% and 25% of trajectories remain as the parent MVK-oxide and MACR-oxide molecules, respectively. Additionally, at most only 5% of the dissociating trajectories form O (3 P) + MVK/MACR (T1 ) products, with a greater fraction forming O (1 D) + MVK/MACR (S0 ) products (cf. CH2 OO). This latter observation coupled with the greater fraction of undissociated trajectories aligns with thebathochromic shift in the electronic absorption of the MACR-oxide and MVK-oxide (cf. CH2 OO). We discuss the implications of the results in a broader context, including those that are relevant to the atmosphere.

Metal organic frameworks derived functional materials for energy and environment related sustainable applications

With the vigorous development of industrial economy, energy and environmental problems have become the most serious issues affecting people's production and life. Therefore, the demand for clean energy production, effective separation and storage is growing. Metal-organic frameworks (MOFs), as a kind of porous crystalline materials with large surface area and porosity, which is self-assembled by metal ions or clusters and organic ligands through coordination bonds. Thanks to a number of unique characteristics such as adjustable pore environment, homogeneous void structure, abundant active sites, unprecedented chemical composition tunability and functional versatility, it has been widely studied, especially for the clean energy conversion in catalysis. In this review, we focus on the research progress of clean energy in catalysis based on MOFs. Emphasis is placed on MOFs with different structures of compositions and their applications in catalytic for clean energy conversion, such as CO oxidation, CO2 reduction and H2 evolution. In addition, the situation of MOFs assisting environmental remediation is also briefly described. Finally, the prospects and challenges of MOFs in clean energy and the remaining issues in this field are presented.

Nanoporous Single-Crystalline Oxide Catalysts for Preferential Oxidation of CO in H2 with an Ultra-wide Temperature Window.

Preferential oxidation of CO in H2 (PROX) reaction is a promising solution to the on-board purification of CO-contaminated H2 fuel for use in next-generation proton-exchange membrane fuel cells (PEMFC). However, achieving high CO selectivity, activity and structural stability across the wide temperature window remains a great challenge. Herein, we fabricate centimeter scale interfacial PROX catalysts grown from nanoporous single-crystalline Pr2 O3 and Nd2 O3 monoliths with lattice surface-deposited Pt clusters at nanoscale. We demonstrate complete and selective removal of CO in H2 over an unprecedented wide temperature window (253-403 K). The monoliths are integrated with an operational PEMFC to purify the H2 fuel contaminated with CO (30 ppm) and enable stable power output for >400 h; over two thousand times longer than without. This work demonstrates that the nanoporous single-crystalline oxide monoliths can simultaneously achieve the stability and overall performance required to realize practically useful PEMFCs.

Nanoporous Single‐Crystalline Oxide Catalysts for Preferential Oxidation of CO in H2 with an Ultra‐wide Temperature Window

AbstractPreferential oxidation of CO in H2 (PROX) reaction is a promising solution to the on‐board purification of CO‐contaminated H2 fuel for use in next‐generation proton‐exchange membrane fuel cells (PEMFC). However, achieving high CO selectivity, activity and structural stability across the wide temperature window remains a great challenge. Herein, we fabricate centimeter scale interfacial PROX catalysts grown from nanoporous single‐crystalline Pr2O3 and Nd2O3 monoliths with lattice surface‐deposited Pt clusters at nanoscale. We demonstrate complete and selective removal of CO in H2 over an unprecedented wide temperature window (253–403 K). The monoliths are integrated with an operational PEMFC to purify the H2 fuel contaminated with CO (30 ppm) and enable stable power output for >400 h; over two thousand times longer than without. This work demonstrates that the nanoporous single‐crystalline oxide monoliths can simultaneously achieve the stability and overall performance required to realize practically useful PEMFCs.

In-situ synthesis of [Ni(tzba)0.5(F)(bpy)] membrane with high H2 permeability through ultramicropores and selective CO2 adsorption with strong affinity of uncoordinated N-Ni-F− active sites

To simultaneously purify H2 and capture CO2 in the steam methane reforming (SMR) process for H2 production, a bifunctional metal organic framework (MOF) membrane ([Ni(tzba)0.5(F)(bpy)]) was proposed via an in-situ synthesis method to efficiently permeate H2 through ultramicropores and selectively adsorb CO2 with the strong affinity of uncoordinated N-Ni-F− active sites. Ni(tzba)0.5(F)(bpy) exhibited a good CO2 uptake capacity (4.3 mmol/g at 273 K and 110 kPa) because the F− anionic and exposed uncoordinated tetrazolate N atoms in ligands have an excellent affinity to CO2. Dynamic breakthrough experiments suggested that Ni(tzba)0.5(F)(bpy) achieved efficient separation of CO2 from H2, CH4, and N2. Ni(tzba)0.5(F)(bpy) MOF membrane also shows outstanding H2/CO2 separation performance because the high adsorption capacity of CO2 reduced CO2 mobility. The H2 permeability of 1.59 × 105 Barrer and H2/CO2 ideal selectivity of 14.43 greatly exceeded the latest upper bound. Continuous permeability tests of up to 100 h demonstrated the long-term stability of the Ni(tzba)0.5(F)(bpy) MOF membrane for H2 separation applications. Density functional theory (DFT) calculations clarified the adsorption mechanism of Ni(tzba)0.5(F)(bpy) towards gases.

Construction of dual active sites on the CuAg plasmonic aerogel for simultaneously efficient photocatalytic CO2 reduction and H2 production

Photocatalytic CO2 reduction and H2 production are a competitive reaction, and existing active sites cannot take into account the simultaneous gas-solid and liquid-solid reaction processes. Hence, a metallic aerogel (CuAg2.5) with dual active sites was constructed via straightforward in-situ reduction process. CuAg2.5 aerosol has larger porosity and CO2 adsorption capacity, which enables H2O and CO2 to fully contact it. The CuAg2.5 can also construct the cooperative dual active sites, which can conduct CO2 reduction reaction on Ag surface and proton reduction reaction on Cu surface, respectively, thereby efficiently guiding the rapid migration of photogenerated carriers. The yields of CO (18533 µmol g−1) and H2 (20340 µmol g−1) for CuAg2.5 are much higher than those of single metals. The ratio of CO and H2 can also regulated via changing the ratio of Ag and Cu. This work gives new insights into the fabrication of unique high-efficiency plasmonic photocatalysts.

Catalytic steam reforming of methanol over highly active catalysts derived from PdZnAl-type hydrotalcite on mesoporous silica MCM-48

A kind of composite material PdZnAl(HT)/MCM-48 was synthesized by dispersing PdZnAl-type hydrotalcite (denoted as PdZnAl(HT)) on mesoporous silica MCM-48. PdZnAl(HT) was confirmed to be formed on the MCM-48 in small particles, and the small PdZnAl(HT) particles easily collapsed during increasing the temperature. A kind of novel PdZn(Al)O/MCM-48 catalyst was obtained after calcining and reducing the PdZnAl(HT)/MCM-48 precursor. PdZn alloy species were formed on the PdZnAl(HT)/MCM-48 after reducing in H2 at 673 K. PdZn(Al)O/MCM-48-2 (with a mass ratio of PdZn(Al)O to MCM-48 = 1) had a large BET surface area (431 cm2 g−1) and small size of PdZn particles (4.1 nm) at the same time. In the steam reforming of methanol, the catalytic stability of PdZn(Al)O/MCM-48-2 was much higher than that of the Cu-based catalyst CuZn(Al)O at 503 K. The methanol conversion over PdZn(Al)O/MCM-48-2 greatly increased with increasing reaction temperature and reached 99% at 513 K. PdZn(Al)O/MCM-48-2 showed higher catalytic activity than PdZnAl(HT) and PdZn/MCM-48 (imp) at the same reaction temperature. The initial CO2 selectivity and H2 selectivity over PdZn(Al)O/MCM-48-2 at 503 K were 99.6 and 99.4%, respectively. Moreover, PdZn(Al)O/MCM-48-2 showed the highest rate of H2 production among various catalysts in the steam reforming of methanol. In a long-time operation, the methanol conversion over PdZn(Al)O/MCM-48-2 decreased from 75.8 to 68.5% after 50 h on stream at 503 K. The size of PdZn particles did not increase after 50 h on stream but the carbonaceous deposits on the catalyst surface caused the deactivation. The deactivated catalyst could be regenerated by calcining in the air at 723 K followed by reducing in the H2 at 673 K. The carbonaceous deposits were eliminated by calcining in the air and the PdZn active species were formed again by reducing in H2.

Experimental studies on poisoning of La0.9Ce0.1Ni5 based hydrogen purification system with CO2 as impurity

In the present study, bed poisoning characteristics of CO2 as gaseous impurity in the La0.9Ce0.1Ni5 based, “Metal Hydride Hydrogen Purification System (MHHPS)” and regeneration of poisoned bed are reported. The study was conducted by varying impurity content of CO2 gas in the H2–CO2 mixture, in the range of 10–50% by weight and the cyclic stability of alloy was tested with 10% CO2 in H2–CO2 mixture. The study was conducted on a lab scale reactor with 6 embedded cooling tube (ECT) filled with 1.2 kg of La0.9Ce0.1Ni5. According to the experimental outcomes, the MHHPS was capable of delivery 99.99% pure hydrogen for CO2 impurity up to 20%. However, for higher impurities level (20–50%), the purity level was in the range of 97.3–99.8%. With CO2 as impurity, significant drop in the absorption capacity of the MHHPS was observed, which was in the range of 0.92 wt% to 0.67 wt% for impurity of 10–50%. However, the bed regeneration was performed, wherein the bed was desorbed and evacuated at 95 °C and 10−2 mbar, followed by absorption of pure hydrogen at 20 bar and 25 °C. Within 2-3 regeneration cycle, the alloy got regenerated and achieved storage capacity of 1.27 wt% in 200 s.

Effects of Silica Modification (Mg, Al, Ca, Ti, and Zr) on Supported Cobalt Catalysts for H2-Dependent CO2 Reduction to Metabolic Intermediates.

Serpentinizing hydrothermal systems generate H2 as a reductant and harbor catalysts conducive to geochemical CO2 conversion into reduced carbon compounds that form the core of microbial autotrophic metabolism. This study characterizes mineral catalysts at hydrothermal vents by investigating the interactions between catalytically active cobalt sites and silica-based support materials on H2-dependent CO2 reduction. Heteroatom incorporated (Mg, Al, Ca, Ti, and Zr), ordered mesoporous silicas are applied as model support systems for the cobalt-based catalysts. It is demonstrated that all catalysts surveyed convert CO2 to methane, methanol, carbon monoxide, and low-molecular-weight hydrocarbons at 180 °C and 20 bar, but with different activity and selectivity depending on the support modification. The additional analysis of the condensed product phase reveals the formation of oxygenates such as formate and acetate, which are key intermediates in the ancient acetyl-coenzyme A pathway of carbon metabolism. The Ti-incorporated catalyst yielded the highest concentrations of formate (3.6 mM) and acetate (1.2 mM) in the liquid phase. Chemisorption experiments including H2 temperature-programmed reduction (TPR) and CO2 temperature-programmed desorption (TPD) in agreement with density functional theory (DFT) calculations of the adsorption energy of CO2 suggest metallic cobalt as the preferential adsorption site for CO2 compared to hardly reducible cobalt-metal oxide interface species. The ratios of the respective cobalt species vary depending on the interaction strength with the support materials. The findings reveal robust and biologically relevant catalytic activities of silica-based transition metal minerals in H2-rich CO2 fixation, in line with the idea that autotrophic metabolism emerged at hydrothermal vents.

The photocatalytic hydrogen evolution and photoreduction CO2 selective enhancement of Co3O4/Ti3+-TiO2/NiO hollow core-shell dual pn junction

The potential and threshold would be the most important issues for photocatalysis, including hydrogen evolution reaction (HER) and CO2 selective photoreduction. The Co3O4/Ti3+-TiO2/NiO hollow core-shell heterojunction is fabricated via a continuous chemical-hydrothermal-annealing-reduction method. As demonstrated, the as-prepared Co3O4/Ti3+-TiO2/NiO hollow core-shell heterojunction exhibits remarkable photocatalytic performance enhancement than single TiO2, including H2 evolution (∼2134.63 μmol/g∙h, ∼80 folds) and CO2 photoreduction (H2/CH4/CO: ∼34.85/132.25/12.65 μmol/g∙h, ∼30 folds), and achieves enhanced CO2 photoreduction selectivity, which can be mainly ascribed to the synergism of Ti3+/Ov and dual pn junction. There, the Ti3+/Ov can not only increase the solar efficiency, but also decrease the threshold of H2O*→H* and *CO→*CHO to enhance HER and CH4 selectivity, including promote H+ diffusion and H2O/CO2/*CO absorption. All these can be supported by the density functional theory (DFT) calculation. Additionally, the formed Co3O4/Ti3+-TiO2/NiO dual pn junction can promote the photo-generated carrier separation/transport efficiently. Furthermore, the hollow core-shell structure obtained by Cobalt 2-methylimidazole (ZIF-67) self-template can increase solar efficiency, and the NiO nanosheets and Co3O4 nanoparticles can increase active sites.

Synergy of yolk-shelled structure and tunable oxygen defect over CdS/CdCO3-CoS2: Wide band-gap semiconductors assist in efficient visible-light-driven H2 production and CO2 reduction

Yolk-shelled CoS2 nanospheres are designed through Kirkendall Effect and subsequently converted into defect-rich CdS/CdCO3-CoS2 photocatalysts via in-situ growth method. The optimal CdS/CdCO3-CoS2 exhibits a significant hydrogen evolution rate of 64867.88 μmol h−1 gcat−1 that is 3.23 and 49.45 folds higher than CoS2-CdS and pure CdS. CO2 reduction rate of CdS/CdCO3-CoS2 is detected additionally (654.7 μmol h−1 gcat−1). Yolk-shelled CdS/CdCO3-CoS2 induces the multi-scattering of incident light, possessing 1.52-fold H2 production rate than that of full hollow ones. Enhanced photoexcited-carriers migration efficiency is attributed to the synergistic effect between possible Mie resonance at about λ = 450 nm in yolk-shelled architecture based on Mie’s theory and monochromatic light HER test, and the formation of defect energy level within the wide-band gap of CdCO3 in Schottky-type/type II heterojunction. Electron paramagnetic resonance, positron annihilation spectroscopy and density functional theory calculation etc. are employed to validate the presence of oxygen vacancies and the photocatalytic mechanism.

Ca12Al14O33 or MgO supported Ni-carbide slag bi-functional materials for H2 production and CO2 capture in sorption-enhanced steam gasification of cellulose/polyethylene mixture

Co-gasification of biomass and waste plastics is a promising technology for H2 production. In this work, Ni-CaO-Ca12Al14O33 and Ni-CaO-MgO bi-functional materials were prepared from carbide slag for H2 production in sorption-enhanced steam gasification experiments of cellulose/polyethylene mixtures. The H2 production and CO2 capture performances of Ni-CaO-Ca12Al14O33 and Ni-CaO-MgO in sorption-enhanced steam gasification of cellulose/polyethylene were studied and compared. Density functional theory calculations, including the density of states, electron differential densities, and adsorption energies were performed to investigate the effect of supports on the stability and reactivity of Ni-CaO-based bifunctional materials at a microscopic level. The results exhibit that polyethene contributes to improving the H2 production effectiveness of cellulose sorption-enhanced steam gasification, the optimum mass ratio of cellulose to polyethene is 0.5:0.5. The CO2 capture capacity, H2 yield, and H2 concentration using Ni-CaO-Ca12Al14O33 can be respectively 2.0, 2.6, and 1.4 times as high as those using Ni-CaO-MgO in the 20th cycle, which indicates the higher cyclic stability and catalytic activity of Ni-CaO-Ca12Al14O33. Density functional theory results also indicate that Ca12Al14O33 can better retain the stable structure of Ni-CaO-based materials, which is consistent with the experimental results. Compared with MgO, Ca12Al14O33 is a better framework for Ni-CaO-based bifunctional material for H2 production in the sorption-enhanced steam gasification process.

Design of efficient noble metal single-atom and cluster catalysts toward low-temperature preferential oxidation of CO in H2

The preferential oxidation of CO in H2 is attractive for the removal of trace amounts of CO to meet the requirement of proton-exchange membrane fuel cells (PEMFCs) application. The key is to design highly effective catalysts that work well in a wide range of low temperatures. Here, the recent progress in Au and Pt group metal catalysts for the PROX reaction is summarized, covering those with single-atom and cluster dispersed metal species with remarkable performance. Firstly, the progress of some representative catalysts is overviewed, with an emphasis on the strategies for improving low-temperature activity, selectivity, and stability. Then, special attention is focused on the key parameters affecting performance in the PROX reaction. Moreover, the reaction mechanisms in terms of adsorption and activation of reactants are discussed. Finally, the challenges and opportunities are offered for guiding the design of advanced noble metal catalysts toward the PROX process.

Water Saturated with Pressurized CO2 as a Tool to Create Various 3D Morphologies of Composites Based on Chitosan and Copper Nanoparticles.

Methods for creating various 3D morphologies of composites based on chitosan and copper nanoparticles stabilized by it in carbonic acid solutions formed under high pressure of saturating CO2 were developed. This work includes a comprehensive analysis of the regularities of copper nanoparticles stabilization and reduction with chitosan, studied by IR and UV-vis spectroscopies, XPS, TEM and rheology. Chitosan can partially reduce Cu2+ ions in aqueous solutions to small-sized, spherical copper nanoparticles with a low degree of polydispersity; the process is accompanied by the formation of an elastic polymer hydrogel. The resulting composites demonstrate antimicrobial activity against both fungi and bacteria. Exposing the hydrogels to the mixture of He or H2 gases and CO2 fluid under high pressure makes it possible to increase the porosity of hydrogels significantly, as well as decrease their pore size. Composite capsules show sufficient resistance to various conditions and reusable catalytic activity in the reduction of nitrobenzene to aniline reaction. The relative simplicity of the proposed method and at the same time its profound advantages (such as environmental friendliness, extra purity) indicate an interesting role of this study for various applications of materials based on chitosan and metals.