Kinetics of NiO and NiCl2 hydrogen reduction as precursors and properties of produced Ni/Al2O3 and Ni-Pd/Al2O3 catalysts

Investigating possibilities for synthesis of novel sorbents and catalyst carriers based on ceramics with controlled open porosity

The aim of this study was to investigate a possibility of synthesis of porous ceramics with controlled open porosity, which could be used as sorbents and catalyst supports. Two organic additives were used to obtain open porosity: polystyrene beads and cellulose fibers, which are mixed with kaolin clay powder and the appropriate water content. Samples were sintered at 1050?C for 1h. Characterization of the obtained products included X-ray powder diffraction analysis (XRPD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and elemental CHNS analysis. In addition, porosity was examined by quantification of visual information. The specific surface areas were determined by the Brunauer-Emmett-Teller (BET) method. Also, density and compressive strength of the obtained samples were assessed. It was determined that by sintering, the organic component completely leaves the system. For samples prepared with polystyrene beads and with cellulose fibers, satisfactory mechanical properties were obtained: compressive strengths were 1.42 and 1.56 MPa, respectively. It was noted that significantly higher open porosity was obtained by using polystyrene beads as a sacrificial template (porosity of ~56 %) instead of cellulose fibers (porosity of ~6 %).

Amino-modified hollow alumina spheres: effective adsorbent for Cd2+, Pb2+, As(V), and diclofenac removal

A simple sol-gel method and external gelatinization method of hollow alumina spheres synthesis were developed in this study. The spheres were modified with polyethyleneimine (PEI) producing PEI-Al₂O₃ via (3-glycidyloxypropyl)trimethoxy-silane, GLYMO, linker. Characterization results, obtained using XRD and SEM microscopy revealed spherical geometry with a hollow core of PEI-Al₂O₃ adsorbent. Introduction of a large number of the amino group, 6.9 mmol g^-1, contributes to achieving high adsorption capacities, q_m, of 95.6, 124.9, 61.3, and 125.9 mg g^-1 for Cd²⁺, Pb²⁺, As(V), and DCF, respectively, which is obtained by using the Langmuir model. Thermodynamic studies indicated feasible adsorption and higher spontaneity with temperature increase. The kinetic study conveniently modeled using pseudo-second-order (PSO) and Weber-Morris kinetic model, as well as single resistance mass transfer model, indicated a change of the contribution of diffusional processes during adsorption with a dominance of intra-particle diffusion. The fixed-bed column adsorption data, fitted using Bohart-Adams, Clark, Yoon-Nelson, and Thomas models, showed lower capacity in comparison to batch study, and thus clear potential applicability of PEI-Al₂O₃ was deduced even at a high loading of feed water.

In Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy of Nickel-Catalyzed Hydrogenation Reactions

Synthesis methods to prepare lower transition metal catalysts and specifically Ni for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) are explored. Impregnation, colloidal deposition, and spark ablation have been investigated as suitable synthesis routes to prepare SHINERS-active Ni/Au@SiO2 catalyst/Shell-Isolated Nanoparticles (SHINs). Ni precursors are confirmed to be notoriously difficult to reduce and the temperatures required are generally harsh enough to destroy SHINs, rendering SHINERS experiments on Ni infeasible using this approach. For colloidally synthesized Ni nanoparticles deposited on Au@SiO2 SHINs, stabilizing ligands first need to be removed before application is possible in catalysis. The required procedure results in transformation of the metallic Ni core to a fully oxidized metal nanoparticle, again too challenging to reduce at temperatures still compatible with SHINs. Finally, by use of spark ablation we were able to prepare metallic Ni catalysts directly on Au@SiO2 SHINs deposited on a Si wafer. These Ni/Au@SiO2 catalyst/SHINs were subsequently successfully probed with several molecules (i. e. CO and acetylene) of interest for heterogeneous catalysis, and we show that they could be used to study the in situ hydrogenation of acetylene. We observe the interaction of acetylene with the Ni surface. This study further illustrates the true potential of SHINERS by opening the door to studying industrially relevant reactions under in situ or operando reaction conditions.

Template-Free Synthesis of Nanoporous Nickel and Alloys as Binder-Free Current Collectors of Li Ion Batteries

This paper reports a versatile template-free method based on the hydrogen reduction of metallic salts for the synthesis of nanoporous Ni and alloys. The approach involves thermal decomposition and reduction of metallic precursors followed with metal cluster nucleation and ligament growth. Topological disordered porous architectures of metals with a controllable distribution of pore size and ligament size ranging from tens of nanometers to micrometers are synthesized. The reduction processes are scrutinized through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The formation mechanism of the nanoporous metal is qualitatively explained. The as-prepared nanoporous Ni was tested as binder-free current collectors for nickel oxalate anodes of lithium ion batteries. The nanoporous Ni electrodes deliver enhanced reversible capacities and cyclic performances compared with commercial Ni foam. It is confirmed that this synthesis method has versatility not only because it is suitable for different types of metallic salts precursors but also for various other metals and alloys.