Perkembangan Teori Sewa Tanah dalam Perspektif Pemikiran Ekonomi

A history of Land Rent Theorities have several opinions, as mazhab of Physiocratic, classical tradition, and new. The different opponions can be understanding for knowing two factors that land value increasingly location to central bussines and fertile soil

Tracking Rh Atoms in Zeolite HY: First Steps of Metal Cluster Formation and Influence of Metal Nuclearity on Catalysis of Ethylene Hydrogenation and Ethylene Dimerization

The initial steps of rhodium cluster formation from zeolite-supported mononuclear Rh­(C₂H₄)₂ complexes in H₂ at 373 K and 1 bar were investigated by infrared and extended X-ray absorption fine structure spectroscopies and scanning transmission electron microscopy (STEM). The data show that ethylene ligands on the rhodium react with H₂ to give supported rhodium hydrides and trigger the formation of rhodium clusters. STEM provided the first images of the smallest rhodium clusters (Rh₂) and their further conversion into larger clusters. The samples were investigated in a plug-flow reactor as catalysts for the conversion of ethylene + H₂ in a molar ratio of 4:1 at 1 bar and 298 K, with the results showing how the changes in catalyst structure affect the activity and selectivity; the rhodium clusters are more active for hydrogenation of ethylene than the single-site complexes, which are more selective for dimerization of ethylene to give butenes

Hydrogen Activation and Metal Hydride Formation Trigger Cluster Formation from Supported Iridium Complexes

The formation of iridium clusters from supported mononuclear iridium complexes in H₂ at 300 K and 1 bar was investigated by spectroscopy and atomic-resolution scanning transmission electron microscopy. The first steps of cluster formation from zeolite-supported Ir­(C₂H₄)₂ complexes are triggered by the activation of H₂ and the formation of iridium hydride, accompanied by the breaking of iridium–support bonds. This reactivity can be controlled by the choice of ligands on the iridium, which include the support

Oxide- and Zeolite-Supported Isostructural Ir(C₂H₄)₂ Complexes: Molecular-Level Observations of Electronic Effects of Supports as Ligands

Zeolite Hβ- and γ-Al₂O₃-supported mononuclear iridium complexes were synthesized by the reaction of Ir­(C₂H₄)₂(acac) (acac is acetylacetonate) with each of the supports. The characterization of the surface species by extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopies demonstrated the removal of acac ligands during chemisorption, leading to the formation of essentially isostructural Ir­(C₂H₄)₂ complexes anchored to each support by two Ir–O_support bonds. Atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM) images confirm the spectra, showing only isolated Ir atoms on the supports with no evidence of iridium clusters. These samples, together with previously reported Ir­(C₂H₄)₂ complexes on zeolite HY, zeolite HSSZ-53, and MgO supports, constitute a family of isostructural supported iridium complexes. Treatment with CO led to the replacement of the ethylene ligands on iridium with CO ligands, and the ν_CO frequencies of these complexes and white line intensities in the X-ray absorption spectra at the Ir L_III edge show that the electron density on iridium increases in the following order on these supports: zeolite HY < zeolite Hβ < zeolite HSSZ-53 ≪ γ-Al₂O₃ < MgO. The IR spectra of the iridium carbonyl complexes treated in flowing C₂H₄ show that the CO ligands were replaced by C₂H₄, with the average number of C₂H₄ groups per Ir atom increasing as the amount of iridium was increasingly electron-deficient. In contrast to the typical supported catalysts incorporating metal clusters or particles that are highly nonuniform, the samples reported here, incorporating uniform isostructural iridium complexes, provide unprecedented opportunities for a molecular-level understanding of how supports affect the electronic properties, reactivities, and catalytic properties of supported metal species

Photocatalytic Water Splitting with Suspended Calcium Niobium Oxides: Why Nanoscale is Better than Bulk – A Kinetic Analysis

The layered Dion–Jacobson phase KCa₂Nb₃O₁₀ is known to catalyze photochemical water reduction and oxidation under UV light in the presence of sacrificial agents. The same reactions are catalyzed by tetrabutylammonium hydroxide-supported HCa₂Nb₃O₁₀ nanosheets obtained by chemical exfoliation of the parent phase. Here we describe a factorial study into the effects of nanoscaling, sacrificial charge donors, cocatalysts, and cocatalyst deposition conditions on the activity of these catalysts. In water, nanoscaling leads to a 16-fold increase in H₂ evolution and an 8-fold increase in O₂ evolution over the bulk phase under the same conditions. The sacrificial electron donor methanol improves H₂ production by 2–3 orders of magnitude to 20–30 mmol of H₂/h/g, while the electron acceptor AgNO₃ increases O₂ production to 400 μmol of O₂/h/g. Rates for H₂ and O₂ evolution further depend on the presence of cocatalysts (Pt or IrO_<i>x</i>) and, in the case of H₂, inversely on their particle size. To rationalize these findings and the increased activity of the nanoscale particles, we propose a kinetic model for photocatalysis with semiconductor particles. The model calculates the electronic rate of the catalysts as a product of terms for charge generation, charge and mass transport, chemical conversion, and charge recombination. The analysis shows that the activity of the catalysts is limited mainly by the kinetics of the redox reactions and by the rate of charge transport to the water–catalyst interface. Mass transport in the solution phase does not play a major role, and neither does surface charge recombination

Ir₆ Clusters Compartmentalized in the Supercages of Zeolite NaY: Direct Imaging of a Catalyst with Aberration-Corrected Scanning Transmission Electron Microscopy

By use of the precursor Ir(CO)₂(acac) (acac is acetylacetonate), a ship-in-a-bottle synthesis was used to prepare Ir₆(CO)₁₆ and, by decarbonylation, clusters well approximated as Ir₆ in the supercages of zeolite NaY. The samples were characterized by infrared and extended X-ray absorption fine structure (EXAFS) spectroscopies and imaged by aberration-corrected scanning transmission electron microscopy with a high-dose electron beam (∼10⁸ e^–/Ǻ², 200 kV), and the catalyst performance was characterized by turnover frequencies for ethene hydrogenation at 298 K and atmospheric pressure. The images characterizing a sample with about 17% of the supercages occupied by decarbonylated nanoclusters indicated clusters well approximated as Ir₆, with diameters consistent with such clusters, and some of the images show the clusters with atomic resolution and indicating each of the 6 Ir atoms. The cluster size was confirmed by EXAFS spectra. Two bonding positions of the Ir₆ clusters in the supercages were distinguished; 25% of the clusters were present at T5 sites and 75% at T6 sites. The results represent the first example of the application of high-dose electron beam conditions to image metal nanoclusters in a nanoporous material; the data are characterized by a high signal-to-noise ratio, and their interpretation does not require any image processing or simulations. These statements are based on images determined in the first 5 s of exposure of the catalyst to the electron beam; thereafter, the electron beam caused measurable deterioration of the zeolite framework and thereupon aggregation of the iridium clusters

Atomically Resolved Site-Isolated Catalyst on MgO: Mononuclear Osmium Dicarbonyls formed from Os₃(CO)₁₂

Supported triosmium clusters, formed from Os₃(CO)₁₂ on MgO, were treated in helium at 548 K for 2 h, causing fragmentation of the cluster frame and the formation of mononuclear osmium dicarbonyls. The cluster breakup and the resultant fragmented species were characterized by infrared and X-ray absorption spectroscopies, and the fragmented species were imaged by scanning transmission electron microscopy. The spectra identify the surface osmium complexes as Os­(CO)₂{O_support}_<i>n</i> (<i>n</i> = 3 or 4) (where the braces denote support surface atoms). The images show site-isolated Os atoms in mononuclear osmium species on MgO. The intensity analysis on the images of the MgO(110) face showed that the Os atoms were located atop Mg columns. This information led to a model of the Os­(CO)₂ on MgO(110), with the distances approximated as those determined by EXAFS spectroscopy, which are an average over the whole MgO surface; the results imply that these complexes were located at Mg vacancies

Direct <i>in Situ</i> Determination of the Mechanisms Controlling Nanoparticle Nucleation and Growth

Although nanocrystal morphology is controllable using conventional colloidal synthesis, multiple characterization techniques are typically needed to determine key properties like the nucleation rate, induction time, growth rate, and the resulting morphology. Recently, researchers have demonstrated growth of nanocrystals by <i>in situ</i> electron beam reduction, offering direct observations of single nanocrystals and eliminating the need for multiple characterization techniques; however, they found nanocrystal morphologies consistent with two different growth mechanisms for the same electron beam parameters. Here we show that the electron beam current plays a role analogous to the concentration of reducing agent in conventional synthesis, by controlling the growth mechanism and final morphology of silver nanocrystals grown via <i>in situ</i> electron beam reduction. We demonstrate that low beam currents encourage reaction limited growth that yield nanocrystals with faceted structures, while higher beam currents encourage diffusion limited growth that yield spherical nanocrystals. By isolating these two growth regimes, we demonstrate a new level of control over nanocrystal morphology, regulated by the fundamental growth mechanism. We find that the induction threshold dose for nucleation is independent of the beam current, pixel dwell time, and magnification being used. Our results indicate that <i>in situ</i> electron microscopy data can be interpreted by classical models and that systematic dose experiments should be performed for all future <i>in situ</i> liquid studies to confirm the exact mechanisms underlying observations of nucleation and growth

Quality of Graphite Target for Biological/Biomedical/Environmental Applications of ¹⁴C-Accelerator Mass Spectrometry

Catalytic graphitization for ¹⁴C-accelerator mass spectrometry (¹⁴C-AMS) produced various forms of elemental carbon. Our high-throughput Zn reduction method (C/Fe = 1:5, 500 °C, 3 h) produced the AMS target of graphite-coated iron powder (GCIP), a mix of nongraphitic carbon and Fe₃C. Crystallinity of the AMS targets of GCIP (nongraphitic carbon) was increased to turbostratic carbon by raising the C/Fe ratio from 1:5 to 1:1 and the graphitization temperature from 500 to 585 °C. The AMS target of GCIP containing turbostratic carbon had a large isotopic fractionation and a low AMS ion current. The AMS target of GCIP containing turbostratic carbon also yielded less accurate/precise ¹⁴C-AMS measurements because of the lower graphitization yield and lower thermal conductivity that were caused by the higher C/Fe ratio of 1:1. On the other hand, the AMS target of GCIP containing nongraphitic carbon had higher graphitization yield and better thermal conductivity over the AMS target of GCIP containing turbostratic carbon due to optimal surface area provided by the iron powder. Finally, graphitization yield and thermal conductivity were stronger determinants (over graphite crystallinity) for accurate/precise/high-throughput biological, biomedical, and environmental¹⁴C-AMS applications such as absorption, distribution, metabolism, elimination (ADME), and physiologically based pharmacokinetics (PBPK) of nutrients, drugs, phytochemicals, and environmental chemicals

Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz–Slyozov–Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution