In particle formation, the method can be just as important as the chemical reaction involved. A new method of synthesizing hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg1 - x Al x (OH)2] x +(CO3 2-) x/ 2·yH2O (x = 1.7−3.3) is reported. The key features of this method are a very rapid mixing and nucleation process in a colloid mill followed by a separate aging process. The properties of the resulting LDHs are compared with those of materials produced using the conventional coprecipitation process at constant pH. The compositions and structural parameters of the materials synthesized using the two routes are very similar, although the crystallinity is slightly higher for the LDHs produced using the new method. The thermal behavior of the materials synthesized using the two routes is also similar. The major advantage of the new method is that it affords smaller crystallites with a higher aspect ratio, having a very narrow distribution of crystallite size. In the conventional coprecipitation process at constant pH, the mixing process takes considerable time such that nuclei formed at the beginning of the process have a much longer time to undergo crystal growth than those formed at the end of the process. The consequence is that a wide dispersion of crystallite sizes is obtained. In the colloid mill process, however, the mixing and nucleation are complete in a very short time and are followed by a separate aging process. Furthermore, we suggest that the extreme forces to which the nucleation mixture is subjected in the colloid mill prevent aggregation of the nuclei and result in the nuclei having a uniform small size. When the resulting mixture is aged in a separate process, well-formed crystallites with a similarly narrow range of diameters result.

No abstract

Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation. The present study reveals the active sites for efficient C–H bond activation in C1–C4 alkanes over ZrO2 free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C–H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO2 can be controlled through adjusting the crystallite size. Accordingly designed ZrO2 shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrOx, GaOx or VOx species.

Novel NiFe 2 O 4 nanorod-graphene composites were synthesized by a facile one-step hydrothermal process in the presence of 1-propyl-3-hexadecylimidazolium bromide ([PHeIm][Br]). The structure and morphology of as-prepared hybrid materials were characterized by FESEM, TEM, HRTEM, AFM, XRD, FTIR, XPS and Raman spectroscopy. The results showed that uniform NiFe 2 O 4 nanorods with a typical length of about 400 nm and a diameter of about 50 nm were well distributed on graphene sheets. The magnetic and electromagnetic parameters were measured using a vibrating sample magnetometer and a vector network analyzer, respectively. The obtained composites exhibited a saturation magnetization of 22.5 emu g À1 and a coercivity of 48.67 Oe at room temperature. A minimum reflection loss of À29.2 dB was observed at 16.1 GHz with a thickness of 2.0 mm, and the effective absorption frequency (RL < À10 dB) ranged from 13.6 to 18 GHz, indicating the excellent microwave absorption performance of the novel composites in the range of 13.6-18 GHz. The absorbing performance of the NiFe 2 O 4 nanorodgraphene composites was better than that of the NiFe 2 O 4 nanoparticle-graphene composites.

No abstract

Nb(2)O(5) nanorods and nanospheres were synthesized, and their photocatalytic activity for methylene blue decomposition in water compared. Nb(2)O(5) nanorods clearly displayed higher activity, despite their comparable surface area. With a shape-dependent surface acidity, hydrothermal stability, and high photoactivity, these Nb(2)O(5) nanorods are a unique and exciting nanomaterial for non-classical photocatalytic mineralization of organic compounds in water.

The electrochemical conversion of N2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3) production. Considering the chemical inertness of N2, rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C‐doped TiO2/C (C‐TixOy/C) material derived from the metal–organic framework (MOF) MIL‐125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal‐based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti−C bonds in C‐TixOy. This binding motive is found to be energetically more favorable for N2 activation compared to the non‐substituted OVs in TiO2. This work elucidates that electrochemical N2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides.

Niobium pentoxide (Nb2O5) has long been known to catalyze unique acid induced reactions, redox reductions and photo-catalytic reactions, etc. Recently, there have been significant advancements in tailoring the oxide materials with controlled structures and morphologies using nano-chemical synthesis by the help of surfactant or stabilizer for optimal catalytic performance. In this short review, we will particularly highlight these synthetic methods for preparation of Nb2O5 nanostructures, their potential applications in catalysis and their structure-activity relationships