Highly Selective Au/ZnO via Colloidal Deposition for CO2 Hydrogenation to Methanol: Evidence of AuZn Role

Gold, Au nanoparticles were deposited on ZnO, Al2O3, and Ga2O3 via colloidal method in order to investigate the role of support for CO2 hydrogenation to methanol. Au/ZnO was also produced using impregnation method to investigate the effect of colloidal method to improve methanol selectivity. Au/ZnO produced via sol immobilization showed high selectivity towards methanol meanwhile impregnation method produced Au/ZnO catalyst with high selectivity towards CO. The CO2 conversion was also influenced by the amount of Au weight loading. Au nanoparticles with average diameter of 3.5 nm exhibited 4% of CO2 conversion with 72% of methanol selectivity at 250 °C and 20 bar. The formation of AuZn alloy was identified as active sites for selective CO2 hydrogenation to methanol. Segregation of Zn from ZnO to form AuZn alloy increased the number of surface oxygen vacancy for CO2 adsorption to form formate intermediates. The formate was stabilized on AuZn alloy for further hydrogenation to form methanol.  The use of Al2O3 and Ga2O3 inhibited the formation of Au alloy, and therefore reduced methanol production. Au/Al2O3 showed 77% selectivity to methane, meanwhile Au/Ga2O3 produced 100% selectivity towards CO. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Ni Nanoparticles on Reducible Metal Oxides (Sm2O3, CeO2, ZnO) as Catalysts for CO2 Methanation

The activity of reducible metal oxide Sm2O3, CeO2, and ZnO as Ni nanoparticles support was investigated for CO2 methanation reaction. CO2 methanation was carried out between 200 °C to 450 °C with the optimum catalytic activity was observed at 450 °C. The reducibility of the catalysts has been comparatively studied using H2-Temperature Reduction Temperature (TPR) method. The H2-TPR analysis also elucidated the formation of surface oxygen vacancies at temperature above 600 °C for 5Ni/Sm2O3 and 5Ni/CeO2. The Sm2O3 showed superior activity than CeO2 presumably due to the transition of the crystalline phases under reducing environment. However, the formation of NiZn alloy in 5Ni/ZnO reduced the ability of Ni to catalyze methanation reaction. A highly dispersed Ni on Sm2O3 created a large metal/support interfacial interaction to give 69% of CO2 conversion with 100% selectivity at 450 °C. The 5Ni/Sm2O3 exhibited superior catalytic performances with an apparent phase transition from cubic to a mixture of cubic and monoclinic phases over a long reaction, presumably responsible for the enhanced conversion after 10 h of reaction. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Influence of TiO2 structural structural properties on photocatalytic hydrogen gas production

A range of commercially produced TiO 2 TiO2 was deposited with Pd nanoparticles and the activities of the anaerobic, ambient temperature photocatalytic hydrogen production from water-methanol mixture were evaluated. The photocatalytic reactions were carried out in the liquid and gas phase conditions with the rate of hydrogen evolutions were higher was when in the gas phase. The Pd/TiO 2 Pd/TiO2 catalysts were characterised using XRD, N 2 N2 adsorption, infrared and XPS in order to investigate the influence of structural properties of TiO 2 TiO2 in determining photocatalytic activity. A positive relationship was established in the rate of hydrogen production from the gas and liquid phase conditions with the size of crystallite TiO 2 TiO2 . Analysis of the surface properties of TiO 2 TiO2 using XPS shows the presence of surface hydroxyl that also influenced the photocatalytic activity of TiO 2 TiO2

The Influence Of Pd Nanoparticle Size On Pd/TiO2 Catalysts For Cinnamaldehyde Hydrogenation Reaction

Palladium nanoparticles (PdNP) supported onto the anatase phase of TiO2 were successfully synthesised using a colloidal method. This synthesis method involved the reduction of K2PdCl4 solution by NaBH4 at different temperatures (1, 25, 50, 75oC) and stabilised with PVA ligand. Transmission electron microscope (TEM) was used to determine the particle size of PdNP on the TiO2. Colloidal synthesis at 1oC and 25oC produced PdNP with less than a 3 nm diameter, whereas when the synthesis temperatures were higher than 25oC, PdNP were produced with a size larger than 4 nm. The catalytic activity of Pd/TiO2 was significantly improved when palladium (Pd) was produced at 1oC with high selectivity towards the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde. The conversion and selectivity trends from the cinnamaldehyde hydrogenation reaction demonstrated the influence of Pd nanoparticle size to provide active sites for the reduction of C=C and C=O bonds. Pd with a diameter of 2.58 nm favoured hydrogenation of C=C bond to produce high selectivity towards hydrocinnamaldehyde, meanwhile a large Pd diameter > 4 nm allowed simultaneaous reduction of C=C and C=O bonds to give comparable selectivity between hydrocinnamaldehyde and hydrocinnamylalcohol

Correction to: Solvent free synthesis of PdZn/TiO2 catalysts for the hydrogenation of CO2 to methanol

The article Solvent Free Synthesis of PdZn/TiO2 Catalysts for the Hydrogenation of CO2 to Methanol by Hasliza Bahruji, Jonathan Ruiz Esquius, Michael Bowker, Graham Hutchings, Robert D. Armstrong, Wilm Jones was originally published Online First without open access. After publication in volume 61, issue 3–4, pages 144–153, the author decided to opt for Open Choice and to make the article an open access publication. Therefore, the copyright of the article has been changed to ©The Author(s) 2018 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made

Hydrogen generation by photocatalytic reforming of potential biofuels: polyols, cyclic alcohols and saccharides

We have studied hydrogen gas production using photocatalysis from C2-C5 carbon chain polyols, cyclic alcohols and mono and di-saccharides using palladium nanoparticles supported on a TiO2 catalyst. For many of the polyols the hydrogen evolution rate is found to be dictated by the number of hydroxyl groups and available α-hydrogens in the structure. However the rule only applies to polyols and cyclic alcohols, while the sugar activity is limited by the bulky structure of those molecules. There was also evidence of ring opening in photocatalytic reforming of cyclic alcohols that involved dehydrogenation and decarbonylation of α Csingle bondC bond

Synthesis and characterization of zeolite NaX from Bangka Belitung Kaolin as alternative precursor

The potential use of kaolin as silica and alumina precursor for the synthesis of zeolite NaX was investigated in this study. The synthesis involved three steps of reactions; the preparation of seed gel, the formation of feedstock gel using kaolin and the combination of overall gel followed by hydrothermal treatment at 105°C for 12 hours. Analysis using X-ray Diffraction (XRD) method indicated the transformation of kaolin into pure phase zeolite NaX with a small amount of kaolin was still visible. Detail microscopic analysis showed the morphology of zeolite X consisted of octahedral particles with a crystallite diameter of 20-30 μm. Analysis of surface acidity using pyridine as probe molecule indicated the zeolite X has high Brǿnsted acidity with 0.181 mmol/g of acid sites, significantly higher than Lewis acidity ~0.053 mmol/g. The N2 adsorption-desorption measurement indicated a type IV material with both microporous and mesoporous structures with an average pore size of 1.47 nm for micropore and 3.41 nm for mesoporous

Pd/ZnO catalysts for direct CO2 hydrogenation to methanol

The direct hydrogenation of CO2 into methanol is crucial for providing a means of CO2 fixation and a way to store cleanly produced hydrogen in a more energy-dense and transportable form. Here we have prepared two series of Pd/ZnO catalysts, both by immobilisation of PVA-protected Pd colloids and by Pd impregnation of PdCl2 to investigate structure activity relationships for direct CO2 hydrogenation. Very different performances were found for the different preparation methods, and the Pd loading and pre-reduction of the catalysts were shown to be important factors for optimising methanol yield. The crucial factor for high methanol yield is the formation of a Pd–Zn alloy, either during the reaction itself, or better by high temperature pre-reduction. The formation of the alloy greatly reduces CO production by the reverse water gas shift reaction. The catalysts prepared by sol-immobilisation were relatively stable to thermal treatment. In contrast, the impregnated catalysts were much less thermally stable, due to the presence of remnant chloride on the surface of the catalyst, which was absent for the case of sol immobilisation preparation. The results illustrate the importance of controlling the PdZn particle size and its surface structure for the catalysts to achieve high methanol selectivity (60%, the rest being CO) and conversion (11%) at 250 °C and 20 bar. Selectivity for sol-immobilised catalysts decreases from 60% at 3 nm average diameter, to 20% at 7 nm

Identification of C2-C5 products from CO2 hydrogenation over PdZn/TiO2-ZSM-5 hybrid catalysts

The combination of a methanol synthesis catalyst and a solid acid catalyst opens the possibility to obtain olefins or paraffins directly from CO2 and H2 in one step. In this work several PdZn/TiO2-ZSM-5 hybrid catalysts were employed under CO2 hydrogenation conditions (240-360 °C, 20 bar, CO2/N2/H2 = 1/1/3) for the synthesis of CH3OH, consecutive dehydration to dimethyl ether and further oxygenate conversion to hydrocarbons. No significant changes after 36 h reaction on the methanol synthesis catalyst (PdZn/TiO2) were observed by XRD, XAS or XPS. No olefins were observed, indicating that light olefins undergo further hydrogenation under reaction conditions, yielding the corresponding alkanes. Increasing the aluminium sites in the zeolites (Si:Al ratio 80:1, 50:1 and 23:1) lead to a higher concentration of mild Brønstead acid sites promoting hydrocarbon chain growth