A novel nanomaterial was synthesized using natural ilmenite sand via a simple precipitation method, and its ability to remove dyes in wastewater was evaluated using methylene blue (MB). The nanomaterial was synthesized by neutralizing the acid leachate obtained by Ilmenite sand digestion, followed by drying at 180 °C. It was characterized by X-ray diffractometry, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, and Brunauer, Emmett, and Teller surface area analyzer. Synthesized nanoparticles are a composite of Fe3O4/Fe2TiO5/TiO2 with a surface area of 292.18 m2/g pore size distribution with an average pore size of 1.53 nm and pore volume of 0.202 cc/g. The maximum adsorption capacity of 24.573 mg/g was obtained at pH 10 for 10 mg of the nanomaterial used with 10 mg/L MB. Dye concentration was varied in the range of 10-25 mg/L with 5 mg/L increment where equilibrium adsorption capacities of 24.573, 31.012, 41.443, and 52.259 mg/g were obtained with 10, 15, 20, and 25 mg/L, respectively. The adsorbent dosage varied as 10, 25, 45, 65, and 100 mg, and the highest adsorbent capacity of 24.573 mg/g was obtained with 10 mg of the adsorbent and 10 mg/L MB. Adsorption of MB followed pseudo-second-order kinetics with an adsorption capacity of 24.863 mg/g. The intraparticle diffusion model revealed that the MB adsorb in three different stages, and corresponding intra-particle diffusion constants of 1.50, 2.71, 3.38, and 4.41 g/mg min1/2 were calculated with the above dye concentrations. Adsorption followed the Langmuir isotherm model. Thermodynamics parameters ΔG, ΔH, and ΔS were calculated to be -27.5521 kJ/mol at 298 K, 2.571 kJ/mol, and 0.101 kJ/mol, respectively, in the experiments carried out varying the temperature. Regeneration studies of the adsorbent were carried out for five cycles, indicating some activity loss after each cycle.

X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed reduction (TPR) and temperature-programmed hydride decomposition (TPHD) were employed to elucidate the structures of a series of PdRe/Al2O3 bimetallic catalysts for selective hydrogenation of furfural. TPR evidenced low-temperature Re reduction in the bimetallic catalysts consistent with migration of [ReO4]- (perrhenate) species to hydrogen-covered Pd nanoparticles on highly hydroxylated  Al2O3. TPHD revealed strong suppression of β-PdHx formation in the reduced catalysts prepared by (i) co-impregnation and (ii) [HReO4] impregnation of reduced Pd/Al2O3 indicating formation of Pd-rich alloy nanoparticles; however, reduced catalysts prepared by (iii) [Pd(NH3)4]2+ impregnation of calcined Re/Al2O3 and subsequent re-calcination did not. Re LIII X-ray absorption edge shifts were used to determine average Re oxidation states after reduction at 400°C. XAFS spectroscopy and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) revealed that a reduced 5 wt.% Re/Al2O3 catalyst contained small Re clusters and nanoparticles comprising Re atoms in low positive oxidation states (~1.5+) and incompletely reduced Re species (primarily Re4+). XAFS spectroscopy of the bimetallic catalysts evidenced Pd-Re bonding consistent with Pd-rich alloy formation. Pd and Re total first-shell coordination numbers suggest that either Re is segregated to the surface (and Pd to the core) of alloy nanoparticles and/or segregated Pd nanoparticles are larger than Re nanoparticles (or clusters). The Cowley short-range order parameters are strongly positive indicating a high degree of heterogeneity (clustering or segregation of metal atoms) in these bimetallic catalysts. Catalysts prepared using the Pd(NH3)4[ReO4]2 double complex salt (DCS) exhibit greater Pd-Re intermixing but remain heterogeneous on the atomic scale.

PdRe/Al2O3 catalysts are highly selective for hydrogenation of furfural to furfuryl alcohol (FAL). Moreover, synergy between the metals can result in greater specific activity (higher turnover frequency, TOF) than exhibited by either metal alone. Bimetallic catalyst structure depends strongly on the metal precursors employed and their addition sequence to the support. In this work, PdRe/Al2O3 catalysts were prepared by: (i) co impregnation (CI) and sequential impregnation (SI) of  Al2O3 using HReO4 and Pd(NO3)2, (ii) SI using NH4ReO4 and [Pd(NH3)4(NO3)2], (iii) HReO4 addition to a reduced and passivated Pd/Al2O3 catalyst, and (iv) impregnation with the double complex salt (DCS), [Pd(NH3)4(ReO4)2]. Raman spectroscopy and temperature-programmed reduction (TPR) evidence larger supported PdO crystallites in catalysts prepared using Pd(NO3)2 than [Pd(NH3)4(NO3)2]. Surface [ReO4]- species detected by Raman exhibit TPR peak temperatures from ranging 85 to 260°C (versus 375°C for Re/Al2O3). After H2 reduction at 400°C, the catalysts were characterized by chemisorption, temperature-programmed hydride decomposition (TPHD), CO diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning transmission electron microscopy (STEM) with energy-dispersive x-ray (EDX) spectroscopy. The CI catalyst containing supported Pd-Re alloy crystallites had a TOF similar to Pd/Al2O3 but higher (61%) FAL selectivity. In contrast, catalysts prepared by methods (ii-iv) containing supported Pd-Re nanoparticles exhibit higher TOFs and up to 78% FAL selectivity.