Kinetic modeling of hydrogen generation over nano-Cu (s) /TiO 2 catalyst through photoreforming of alcohols

Partially Reduced Ni-NiO-TiO2 Photocatalysts for Hydrogen Production from Methanol–Water Solution

The study compares the photocatalytic behavior of TiO2, NiO-TiO2, and Ni-NiO-TiO2 photocatalysts in photocatalytic hydrogen production from methanol–water solution. TiO2 and NiO-TiO2 photocatalysts with theoretical NiO loading of 0.5, 1.0, and 3.0 wt. % of NiO were prepared by the sol–gel method. The Ni-NiO-TiO2 photocatalysts were prepared by partial reduction of NiO-TiO2 in hydrogen at 450 °C. The Ni-NiO-TiO2 photocatalysts showed significantly higher hydrogen production than the NiO-TiO2 photocatalysts. The structural, textural, redox, and optical properties of all of the prepared photocatalysts were studied by using XRD, SEM, N2- adsorption, XPS, H2-TPR, and DRS. Attention is focused on the contribution of Ni loading, the surface composition (Ni2+, the lattice O2− species, and OH groups), the distribution of Ni species (dispersed NiO species, crystalline NiO phase, and the metallic Ni0 species), oxygen vacancies, TiO2 modification, the TiO2 crystallite size, and the specific surface area.

Effect of Synthesis Method on Reaction Mechanism for Hydrogen Evolution over CuxOy/TiO2 Photocatalysts: A Kinetic Analysis

The existing literature survey reports rare and conflicting studies on the effect of the preparation method of metal-based semiconductor photocatalysts on structural/morphological features, electronic properties, and kinetics regulating the photocatalytic H2 generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H2 generation synthesized via distinct methods (i.e., photodeposition and impregnation). Our study aims to establish a stringent correlation between physicochemical/electronic properties and photocatalytic performances for H2 generation based on material characterization and kinetic modeling of the experimental outcomes. Estimating unknown kinetic parameters, such as charge recombination rate and quantum yield, suggests a mechanism regulating charge carrier lifetime depending on copper distribution on the TiO2 surface. We demonstrate that H2 generation photoefficiency recorded over impregnated CuxOy/TiO2 is related to an even distribution of Cu(0)/Cu(I) on TiO2, and the formation of an Ohmic junction concertedly extended charge carrier lifetime and separation. The outcomes of the kinetic analysis and the related modeling investigation underpin photocatalyst physicochemical and electronic properties. Overall, the present study lays the groundwork for the future design of metal-based semiconductor photocatalysts with high photoefficiencies for H2 evolution.

Current developments and future trends in photocatalytic glycerol valorization: process analysis

Challenges and opportunities in photocatalytic glycerol valorization to hydrogen and value-added liquid products: process analysis and parametric study.

Improving Glycerol Photoreforming Hydrogen Production Over Ag2O-TiO2 Catalysts by Enhanced Colloidal Dispersion Stability

Solar-driven photocatalytic reforming of biomass-derived resources for hydrogen production offers a sustainable route toward the generation of clean and renewable fuels. However, the dispersion stability of the catalyst particles in the aqueous phase hinders the efficiency of hydrogen production. In this work, a novel method of mixing Ag2O-TiO2 photocatalysts with different morphologies was implemented to promote colloidal dispersion stability, thereby improving hydrogen production performance. A series of Ag2O-TiO2 nanoparticles with different morphologies were synthesized, and their dispersion stabilities in aqueous phase were investigated individually. Two types of Ag2O-TiO2 particles with different morphologies under certain proportions were mixed and suspended in glycerol aqueous solution without adding any dispersant for enhancing dispersion stability while reacting. From the results, photocatalytic hydrogen production was found to be strongly correlated to colloidal dispersion stability. The mixed suspension of Ag2O-TiO2 nanosphere and nanoplate achieved an excellent colloidal dispersion stability without employing any additives or external energy input, and the photoreforming hydrogen production obtained from this binary component system was around 1.1-2.3 times higher than that of the single-component system. From the calculated hydrogen production rate constants between continuous stirring and the binary system, there was only <6% difference, suggesting an efficient mass transfer of the binary system for photoreforming hydrogen production. The proposed method could provide some inspiration to a more energy-efficient heterogeneous catalytic hydrogen production process.

Solar Fuels by Heterogeneous Photocatalysis: From Understanding Chemical Bases to Process Development

The development of sustainable yet efficient technologies to store solar light into high energy molecules, such as hydrocarbons and hydrogen, is a pivotal challenge in 21st century society. In the field of photocatalysis, a wide variety of chemical routes can be pursued to obtain solar fuels but the two most promising are carbon dioxide photoreduction and photoreforming of biomass-derived substrates. Despite their great potentialities, these technologies still need to be improved to represent a reliable alternative to traditional fuels, in terms of both catalyst design and photoreactor engineering. This review highlights the chemical fundamentals of different photocatalytic reactions for solar fuels production and provides a mechanistic insight on proposed reaction pathways. Also, possible cutting-edge strategies to obtain solar fuels are reported, focusing on how the chemical bases of the investigated reaction affect experimental choices.

Sacrificial photocatalysis: removal of nitrate and hydrogen production by nano-copper-loaded P25 titania. A kinetic and ecotoxicological assessment

The photocatalytic removal of nitrate with simultaneous hydrogen generation was demonstrated using zero-valent nano-copper-modified titania (P25) as photocatalyst in the presence of UV-A-Vis radiation. Glycerol, a by-product in biodiesel production, was chosen as a hole scavenger. Under the adopted experimental conditions, a nitrate removal efficiency up to 100% and a simultaneous hydrogen production up to 14 μmol/L of H₂ were achieved (catalyst load = 150 mg/L, initial concentration of nitrate = 50 mg/L, initial concentration of glycerol = 0.8 mol/L). The reaction rates were independent of the starting glycerol concentration. This process allows accomplishing nitrate removal, with the additional benefit of producing hydrogen under artificial UV-A radiation. A kinetic model was also developed and it may represent a benchmark for a detailed understanding of the process kinetics. A set of acute and chronic bioassays (Vibrio fischeri, Raphidocelis subcapitata, and Daphnia magna) was performed to evaluate the potential ecotoxicity of the nitrate/by-product mixture formed during the photocatalytic process. The ecotoxicological assessment indicated an ecotoxic effect of oxidation intermediates and by-products produced during the process.