Heba M. Gobara

Enhanced hydrogen production from water via a photo-catalyzed reaction using chalcogenide d-element nanoparticles induced by UV light

Hydrogen has the potential to meet the requirements as a clean non-fossil fuel in the future. The photocatalytic production of H2 through water splitting has been demonstrated and enormous efforts have been published. The present work is an attempt to enhance the production of H2 during water splitting using synthesized nanoparticles based on chalcogenide d-element semiconductors via a photochemical reaction under UV-light in the presence of methanol as a hole-scavenger. In general, the enhanced activity of a semiconductor is most likely due to the effective charge separation of photo generated electrons and holes in the semiconductors. Hence, the utilization of different semiconductors in combination can consequently provide better hydrogen production. Accordingly in this research work, two different semiconductors, with different concentrations, either used individually or combined together were introduced. They in turn produced a high concentration of H2 as detected and measured using gas chromatography. Herein, data revealed that the nano-structured semiconductors prepared through this work are a promising candidate in the production of an enhanced H2 flux under visible UV radiation.

II. Electrical Properties of Ni/Silica Gel and Pt/γ-Alumina Catalysts in Relation to Catalytic Activity

Abstract The catalytic activity of silica gel and silica gel—supported nickel (2, 5, and 8 wt% Ni) and γ-alumina—supported platinum (0.3 and 0.6 wt% Pt) was studied for n-hexane or n-pentane cracking and cyclohexane dehydrogenation adopting pulse technique. The results showed that Pt/γ-alumina could be a selective catalyst for cyclohexane dehydrogenation reaction. Ni/silica gel catalyst was a good cracking catalyst, the activity of which increased by increasing the metal content up to 8% Ni. For cyclohexane, dehydrogenation over Ni/silica gel, the activity increased by increasing the metal loading. N2 sorption characterizations showed that both silica gel- and γ-alumina—supported catalyst samples exhibited mesoporous structures. Silica gel and silica gel—supported samples have ink-bottle type pores while γ-alumina and γ-alumina—supported platinum samples have platelike pores. BET surface area and total pore volume decreased by increasing metal loading for both catalyst samples. Electrical properties of pure γ-alumina and silica gel supports were functions of metal content and frequency of the applied field. The increase of conductivity is considered a good indicator of the decrease in the activation energy (increase of catalytic activity). The observed increase in conductivity with the increase of metal loading may be due to increase in the mobility of the free charge carriers (i.e., ions and free radicals taking part in the mechanism of catalytic conversion of hydrocarbons over the catalyst polarized active centers that increased by increasing metal loading). These charge carriers diffuse in the bulk of pores and reach electrodes where they discharge, giving rise to diffusion impedance (Warburg impedance).

Can microwave assisted in situ reduction of supported Pt nanoparticles challenge the chemical method in controlling the dispersion profile-catalytic performance relationship?

In this study, Pt (of 0.3, 0.6 and 0.9 wt% loadings) was supported on a mesoporous silica surface via a microwave-assisted solution (MAS) method or rotary chemical evaporation (RCE) method in the in situ reduction step. The as-synthesized Pt nanocatalysts were characterized through XRD, XRF, TGA/DSC, TEM, N2-adsorption–desorption, H2-pulse titration and electrical conductivity techniques. The samples prepared by MAS method exhibited higher surface area and a better dispersion profile of Pt NPs, of average sizes not exceeding 10 nm with increasing the Pt loading. In contrast, although RCE method showed higher efficacy in decomposing the used precursor, an uneven distribution of larger Pt nanoparticles (≥33 nm) was determined. Electrical properties in terms of AC conductivity and dielectric constant confirmed the enhancement of an even distribution of smaller Pt NPs with a higher concentration of grain boundaries effected by microwave electromagnetic radiations. Highly mobile electrons and lattice vibrations (phonons) were favored, as compared with aggregated NPs produced during RCE method. The TOF values calculated for reactions to selectively produce ethylene (from ethanol) or benzene (from cyclohexane) decreased with Pt loading on the catalyst samples synthesized by MAS method. The highly dispersed NPs (of 3–7 nm) seemed to be responsible for the activity in both reactions, probably tending to be structure insensitive. However, samples reduced by RCE method, with enlarged average sizes of surface Pt NPs (approaching 15.5 nm), exhibited increasing TOF values with Pt loading, i.e., causing the reactions most probably to be structure sensitive.

A Comparative Study of Surface Characteristics of Nickel Supported on Silica Gel, γ-Alumina, Aluminosilicate

Abstract Surface characteristics of the prepared nickel catalysts containing 7, 10, and 13 wt% Ni w/w over different supports—silica gel, γ-alumina, and aluminosilicate—were investigated. Surface areas, total pore volumes, and average pore radii were determined for all catalysts. Pore analysis was discussed based on Vl-t plots and pore size distribution. The measured surface areas and pore volumes of pure supports increased in the following order: γ-alumina < aluminosilicate < silica gel. Pore analysis showed that SiO2 and Al2O3-SiO2 and their supported Ni samples were characterized by presence of narrower mesopores of ink-bottle type. Al2O3 was distinguished by presence of two distinct pore types, both showing continual increase in fraction with a shift to larger dimensions upon loading with nickel. Penetration and/or incorporation process of Ni particles took place at the expense of their interaction with Al+3. SiO2 revealed a gradual increase in surface parameters upon loading with nickel. For Al2O3-SiO2—supported samples, the result proposed the interaction of Ni with both alumina and silica contents of the support regardless of the penetration process.

Role of Structure and Acidic Nature on Catalytic Behavior of Nickel Supported H-mordenite, H-ZSM-5, and γ–alumina Catalysts

Abstract Nickel metal was loaded in different percentages (7, 10, and 13% w/w) on different supports (H-mordenite, H-ZSM-5, and γ–alumina). The prepared catalyst samples were tested in cyclohexane conversion using microreactor pulse technique. Structure was followed up by XRD analysis. Chemisorption of tert-butylamine (TBA) was adopted for estimating the number of surface acid sites. It was found that all prepared samples displayed cracking activity, being mostly related to the fraction of acid sites remaining on the surface after coverage with supported Ni atoms. H-mordenite-supported samples exhibited mainly isomerization functionality by showing a larger portion of surface acid sites. H-ZSM-5-supported samples showed higher dehydrogenation activity. Agglomeration seemed to be responsible for lower activity of the sample of higher Ni content. The formed NiOOH phase was suggested to be responsible for increased dehydrogenation activity on H-ZSM-5 samples and increased cracking activity on γ–alumina-supported samples of higher Ni content.

Zn +2 -doped x -Ti–SiO 2 tricomposites for enhancement the photo-catalytic degradation of phenol under UV irradiation

A series of zinc-doped titania–silica tricomposites (Zn/xTi–SiO2) with different Ti-molar ratios were prepared by sol–gel method. Zn+2 ions of 25 wt% were doped on the photo-catalysts using wet impregnation method. The as-synthesized Zn/xTi–SiO2 nano-catalysts were characterized through N2-adsorption–desorption, X-ray diffraction, transmission electron microscope, fourier transform infrared, dynamic light scatterings, photoluminescence, and diffuse reflectance techniques. Photo-catalytic degradation of phenol (PhOH) under 8-W ultraviolet C irradiation was examined. 96% removal was achieved in 150 min by using Zn/20Ti–SiO2. The kinetic study revealed that photo-degradation of PhOH follows pseudo-first order reaction mechanism, where the rate constant was 77.4 × 10−3 min−1. One-way analysis of variance, as well as Student’t-test at α = 0.05 level (95% confidence interval) was performed to comparing the means of the results obtained.Graphical Abstract