PtOx-SnOx-TiO2 catalyst system for methanol photocatalytic reforming: Influence of cocatalysts on the hydrogen production

Effects of modification of PtOx-TiO2 photocatalysts by tin were elucidated by exploring relationships between the structural properties of variously prepared tin-loaded catalysts and their catalytic activity in methanol photocatalytic reforming. Tin free and amorphous tin-oxide decorated TiO2 samples were prepared by sol-gel method from titanium-isopropoxide. In other approach, Sn was loaded onto the sol-gel prepared TiO2 by impregnation followed by calcination. Pt was introduced by impregnation followed by either reduction in H2 at 400 °C or calcination at 300 °C. TEM, XRD and Raman spectroscopic measurements proved that TiO2 existed in the form of aggregates of polycrystalline anatase with primary particle size of 15–20 nm in all samples. Photocatalytic hydrogen production was influenced by the combined effect of many parameters. Both the presence of Sn and the way of Pt co-catalyst formation played important role in the activity of these photocatalysts. The Sn introduction by both sol-gel method and impregnation clearly enhanced the photocatalytic activity. 1H MAS NMR measurements revealed that the Sn introduction reduced the amount of the terminal Ti-OH groups of relatively basic character considered to be unfavorable for the photocatalytic reaction. Presence of SnOx decreased the signal of the undesirable vacancies observed by ESR. Furthermore surface SnOx enhanced the dispersion of Pt. Formation of the Pt co-catalyst by calcination was more favorable than by H2 treatment. In case of the calcined samples in situ reduction of the Pt nanoparticles at the beginning of the photocatalytic reaction was found to be favorable for the hydrogen production. The relatively modest photocatalytical activity obtained after high temperature H2 treatment could be related to at least two processes in this system: (i) creation of unfavorable oxygen vacancies and (ii) segregation of SnOx to the surface of the Pt cocatalyst as the result of the air exposure of the alloy type Pt-Sn nanoparticles formed during the H2 treatment, resulting in a decreased number of active sites for reduction of H+

Controlling Activity and Selectivity Using Water in the Au-Catalysed Preferential Oxidation of CO in H\u3csub\u3e2\u3c/sub\u3e

Industrial hydrogen production through methane steam reforming exceeds 50 million tons annually and accounts for 2–5% of global energy consumption. The hydrogen product, even after processing by the water–gas shift, still typically contains ∼1% CO, which must be removed for many applications. Methanation (CO + 3H2 → CH4 + H2O) is an effective solution to this problem, but consumes 5–15% of the generated hydrogen. The preferential oxidation (PROX) of CO with O2 in hydrogen represents a more-efficient solution. Supported gold nanoparticles, with their high CO-oxidation activity and notoriously low hydrogenation activity, have long been examined as PROX catalysts, but have shown disappointingly low activity and selectivity. Here we show that, under the proper conditions, a commercial Au/Al2O3 catalyst can remove CO to below 10 ppm and still maintain an O2-to-CO2 selectivity of 80–90%. The key to maximizing the catalyst activity and selectivity is to carefully control the feed-flow rate and maintain one to two monolayers of water (a key CO-oxidation co-catalyst) on the catalyst surface

Combinatorial optimization and synthesis of multiple promoted MoVNbTe catalysts for oxidation of propane to acrylic acid

New MoVTeNb multi-component catalysts (so-called M1 phase) were designed and tested using combinatorial and high-throughput methods. An international team of academic institutes and industrial partners has cooperated to understand the chemistry occurring during the hydrothermal synthesis and crystallization of the M1 phase of the MoVTeNb mixed oxide. With this information, the optimization of this catalyst system could be targeted with the aim of improving catalyst performance for short chain alkane – ethane and propane - oxidation reactions. Beside the elements responsible for the formation of the M1 phase (Mo, V, Te, and Nb) and promoters found to be advantageous in our previous work (Mn, Ni, W and citric acid), the following components were added to the synthesis mixture: Ce, Cu, Co, Cr and ethylene glycol. Contrary to the previous approach in this study, the V/Mo, Te/Mo and Nb/Mo ratios were kept constant. Consequently, the experimental space had nine variables. The discrete levels of variables are established in such a way that the number of the potential experimental points in the multi-dimensional experimental space was in the range of 200 000. Five new generations were designed using an optimization platform consisting of holographic optimization algorithm and artificial neural networks. Altogether 250 catalysts were prepared and tested. A complex objective function was created consisting of two independent catalytic performance characteristics – conversion and product selectivity – as well as the expected production costs and prices of the target product acrylic acid (AA) and export steam. The AA production costs were estimated assuming a recycle scheme for such a future AA plant with standard downstream equipment. The best catalysts in the group of catalysts with low vanadium content gave acrylic acid yields of 58% in the high throughput tests after five generations. On the bases of holographic maps, correlations between the composition of the synthesis mixtures and the yields of AA were visualized allowing to see the cross effect between components. Mn and Co had a positive effect, while Cu and Ce resulted in negative effect on the yield of AA. The analysis of the correlation between conversions vs. product yields allowed figuring out the main reaction routes leading to acrylic acid and CO2 in a consecutive reaction scheme. Following this successful high throughput development, the hydrothermal method using the newly identified synthesis aids was further optimized and successfully scaled up to 40 l autoclaves using the cheapest available chemicals, the oxides. This now renders possible the large-scale production of that complex MoVNbTe mixed oxide catalyst