Temperature-vacuum swing adsorption for direct air capture by using low-grade heat

Direct air capture (DAC) is a promising carbon mitigation technology and will likely be part of extensive carbon removal portfolio. Adsorptive DAC is an appropriate option for carbon capture to utilize low-grade heat because of its desirable regeneration temperature and adaptability to be integrated with renewables. Building indoor environment with CO2 concentrations above 1000 ppm provides another suitable scenario for DAC. Herein, DAC using temperature-vacuum swing adsorption (TVSA) is presented and analyzed by integrating various low-grade heat sources in buildings. An amine-functionalized metal organic framework is selected for process simulation, and the performance is compared with those using other sorbents. It indicates that amine-functionalized material has advantages in CO2 productivity and purity. A techno-economic analysis is carried out to explore the benefit of the proposed DAC in buildings. The results show that regeneration by heat pumps at 373 K is the most competitive solution and has 176.7 $·tCO2−1 of the levelized cost of DAC (LCOD). Compared with conventional energy supply, solutions with low-grade heat utilization in buildings could achieve lower carbon intensity and increase by 5.2–25.0% in net LCOD. These results will provide practical guidelines for DAC application with lower energy penalties and costs

Substrate co-doping modulates electronic metal-support interactions and significantly enhances single-atom catalysis

Transitional metal nanoparticles or atoms deposited on appropriate substrates can lead to highly economical, efficient, and selective catalysis. One of the greatest challenges is to control the electronic metal–support interactions (EMSI) between the supported metal atoms and the substrate so as to optimize their catalytic performance. Here, from first-principles calculations, we show that an otherwise inactive Pd single adatom on TiO2(110) can be tuned into a highly effective catalyst, e.g. for O2 adsorption and CO oxidation, by purposefully selected metal–nonmetal co-dopant pairs in the substrate. Such an effect is proved here to result unambiguously from a significantly enhanced EMSI. A nearly linear correlation is noted between the strength of the EMSI and the activation of the adsorbed O2 molecule, as well as the energy barrier for CO oxidation. Particularly, the enhanced EMSI shifts the frontier orbital of the deposited Pd atom upward and largely enhances the hybridization and charge transfer between the O2 molecule and the Pd atom. Upon co-doping, the activation barrier for CO oxidation on the Pd monomer is also reduced to a level comparable to that on the Pd dimer which was experimentally reported to be highly efficient for CO oxidation. The present findings provide new insights into the understanding of the EMSI in heterogeneous catalysis and can open new avenues to design and fabricate cost-effective single-atom-sized and/or nanometer-sized catalysts

Differential stress induced by thiol adsorption on facetted nanocrystals

Polycrystalline gold films coated with thiol-based self-assembled monolayers (SAM) form the basis of a wide range of nanomechanical sensor platforms. The detection of adsorbates with such devices relies on the transmission of mechanical forces, which is mediated by chemically derived stress at the organic-inorganic interface. Here, we show that the structure of a single 300-nm-diameter facetted gold nanocrystal, measured with coherent X-ray diffraction, changes profoundly after the adsorption of one of the simplest SAM-forming organic molecules. On self-assembly of propane thiol, the crystal's flat facets contract radially inwards relative to its spherical regions. Finite-element modelling indicates that this geometry change requires large stresses that are comparable to those observed in cantilever measurements. The large magnitude and slow kinetics of the contraction can be explained by an intermixed gold-sulphur layer that has recently been identified crystallographically. Our results illustrate the importance of crystal edges and grain boundaries in interface chemistry and have broad implications for the application of thiol-based SAMs, ranging from nanomechanical sensors to coating technologies

Desorption characteristics of H₂O and CO₂ from alumina F200 under different feed/purge pressure ratios and regeneration temperatures

Air pre-purification is an important process for industrial air separation with cryogenic distillation method. This process is typically realized by pressure swing adsorption or temperature swing adsorption. H₂O and CO₂ are the two major components to be removed among the contaminants. In this paper, we establish a mathematical model describing the mass and heat balances in the adsorption bed, and the double-component adsorption/desorption equilibriums of H₂O/CO₂ on alumina F200. To conduct desorption performance analysis, a one-cycle process consisting of feed, blowdown, and purge step under different operating conditions, such as feed/purge pressure ratio and regeneration temperature, is numerically studied. The effect of heat on the desorption performance of H₂O and CO₂ is investigated by changing the purge gas temperature within 30–200 °C under feed/purge pressure ratios of 6:1.1 and 10:1.1, respectively. Detailed results of the H₂O and CO₂ adsorption/desorption behaviors in the bed are demonstrated. The mass and heat transfer characteristics during desorption are also analyzed. Suggestions on the optimization of the heating temperature and duration of purge gas are also proposed

House Price Forecasting from Investment Perspectives

Housing market dynamics have primarily shifted from consumption- to investment-driven in many countries, including Australia. Building on investment theory, we investigated market dynamics by placing investment demand at the center using the error correction model (ECM). We found that house prices, rents, and interest rates are cointegrated in the long run under the present value investment framework. Other economic factors such as population growth, unemployment, migration, construction activities, and bank lending were also important determinants of the housing market dynamics. Our forecasting results show that the Sydney housing market will continue to grow with no significant price decline in the foreseeable future.</jats:p

Neural mechanisms of 1-back working memory in intellectually gifted children

To investigate the neural mechanisms underlying intellectually gifted children, electroencephalograms (EEG) were recorded while 13 intellectually gifted children and 13 average children accomplished a 1-back working memory task. The results showed that intellectually gifted children elicited significantly shorter P3 latency than their intellectually average peers. These results support the neural efficiency theory that intellectually gifted individual can use their brain more efficiently

An oxidized magnetic Au single atom on doped TiO2(110) becomes a high performance CO oxidation catalyst due to the charge effect

Catalysis using gold nanoparticles supported on oxides has been under extensive investigation for many important application processes. However, how to tune the charge state of a given Au species to perform a specific chemical reaction, e.g. CO oxidation, remains elusive. Here, using first-principles calculations, we show clearly that an intrinsically inert Au anion deposited on oxygen-deficient TiO2(110) (Au@TiO2(110)) can be tuned and optimized into a highly effective single atom catalyst (SAC), due to the depletion of the d-orbital by substrate doping. Particularly, Ni- and Cu-doped Au@TiO2 complexes undergo a reconstruction driven by one of the two dissociated O atoms upon CO oxidation. The remaining O atom heals the surface oxygen vacancy and results in a stable bow-shaped surface “O–Au–O” species; thereby the highly oxidized Au single atom now exhibits magnetism and dramatically enhanced activity and stability for O2 activation and CO oxidation, due to the emergence of high density of states near the Fermi level. Based on further extensive calculations, we establish the “charge selection rule” for O2 activation and CO oxidation on Au: the positively charged Au SAC is more active than its negatively charged counterpart for O2 activation, and the more positively charged the Au, the more active it is

Microstructure and wear resistance of (Nb,Ti)C carbide reinforced Fe matrix coating with different Ti contents and interfacial properties of (Nb,Ti)C/α-Fe

In this work, the (Nb,Ti)C reinforced Fe matrix coatings were prepared by gas metal arc welding (GMAW) hardfacing technology. The microstructure, hardness and wear resistance of (Nb,Ti)C reinforced coatings with different Ti contents were investigated by experiments. The interfacial properties of (Nb,Ti)C/α-Fe interfaces were calculated by first principles method based on density functional theory (DFT). The experiment results show that as the Ti content in the coating changes from 0.15 to 0.41 wt%, the average diameter of NbC primary carbide grains decreases from 3.2 μm to 1.7 μm and their amount increase from 0.35 to 0.51 μm−2. The coating with 0.15 wt% Ti performs the lowest wear loss, which is 0.47 g/N ∗ cm2. From the calculated results, the interfacial combination between carbide and matrix are improved after Ti addition. The adhesion work of (Nb,Ti)C/Fe interfaces show the following order: CNb-Fe < NbC-Fe < CTiNb-Fe < CNbTi-Fe < NbTiC-Fe < TiNbC-Fe. In CTiNb-Fe, CNbTi-Fe and CNb-Fe surfaces, weak Fe-M covalent bonds are formed at the interfaces. In NbC-Fe, NbTiC-Fe and TiNbC-Fe surfaces, strong Fe–C and M-C covalent bond can be found at (Nb,Ti)C/α-Fe interfaces, besides, Fe–C ionic bonds are also formed

Refinement and homogenization of M7C3 carbide in hypereutectic Fe-Cr-C coating by Y2O3 and TiC

The microstructures of the hypereutectic Fe-Cr-C, Fe-Cr-C-Ti and Fe-Cr-C-Ti-Y2O3 coatings were observed by OM. The phase structures were characterized by XRD and XPS. The elemental distributions were analyzed by EDS. The interface relationship between TiC and nano-Y2O3 were observed by TEM and analyzed by lattice misfit theory. From the metallographic observations, the primary M7C3 carbide can be refined by Ti additive, while it is inhomogeneously distributed. However, the primary M7C3 carbide can also be refined further by adding Ti additive and nano-Y2O3 simultaneously, and it is homogeneously distributed. From the phase constituent analysis, TiC is formed by Ti additive, while TiC and Y2O3 are found by adding Ti additive and nano-Y2O3 simultaneously. From the elemental distribution mappings and TEM images, TiC nucleates upon nano-Y2O3 with orientation relationship {001}Y2O3//{001}TiC in the hypereutectic Fe-Cr-C-Ti-Y2O3 coating. By misfit computation, the lattice misfit between Y2O3 (001) plane and TiC (001) plane is 7.3%, which suggests that Y2O3 can act as the heterogeneous nucleus of TiC so that TiC particles are increased and dispersedly distributed. These numerous dispersed TiC particles can further act as the heterogeneous nucleus of the primary M7C3 carbide, which play a role in refining primary M7C3 carbide and promoting its homogenization