Copper Nitrate Redispersion To Arrive at Highly Active Silica-Supported Copper Catalysts

Abstract

In order to obtain copper catalysts with high dispersions at high copper loadings, the gas flow rate and gas composition was varied during calcination of silica gel impregnated with copper nitrate to a loading of 18 wt % of copper. Analysis by X-ray diffraction (XRD), N2O chemisorption, and transmission electron microscopy (TEM) showed that calcination in stagnant air resulted in very large copper crystallites and a low copper surface area (12 m2·gCu –1). A moderate flow of air was sufficient to greatly enhance the copper surface area (∼90 m2·gCu –1) based on a bimodal particle size distribution of few large crystallites and a highly dispersed phase. Changing to an N2 flow resulted in similar copper surface areas compared to samples calcined in air at the same space velocity, while calcination in a 2% NO/N2 flow resulted in a relatively narrow particle size distribution peaking around 8 nm and a slightly lower copper surface area (84 m2·gCu –1). By use of SBA-15 supported samples, in situ XRD and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) showed that the decomposition of copper nitrate in NO occurred via a highly dispersed copper hydroxynitrate phase, while decomposition in N2 or air occurred partly via copper nitrate anhydrate and partly via poorly dispersed copper hydroxynitrate. The high CuO dispersions after calcination in an N2 or air flow were ascribed to the redispersion of copper nitrate anhydrate by interaction with the OH groups of the silica support. By utilization of this redispersion, high copper dispersions on silica gel with concomitant high activities were obtained for the gas-phase hydrogenation of butanal.

Interplay between pore size and nanoparticle spatial distribution: Consequences for the stability of CuZn/SiO2 methanol synthesis catalysts

“…The experimental Cu/Si ratio was used to derive the local Cu surface and pore volumetric loading (Supplementary equations S1 and S2). atmospheres [52]. Fig.…”

“…Recent mechanistic insights into the synthesis of supported catalysts provide means to control the nanospatial distribution of metal particles on porous carriers [51,52]. We have previously reported on the impact of the gas composition and hydrodynamics during the calcination of ex-nitrate Cu/SiO 2 catalysts on the resulting size and spatial distribution of the metal particles [52].…”

“…We have previously reported on the impact of the gas composition and hydrodynamics during the calcination of ex-nitrate Cu/SiO 2 catalysts on the resulting size and spatial distribution of the metal particles [52]. Addition of small amounts of NO to the gas phase promotes low-temperature hydrolysis of the hydrate nitrate precursor into Cu 2 (OH) 3 NO 3 .…”

Preparation and particle size effects of Ag/α-Al2O3 catalysts for ethylene epoxidation

“…In the present paper we describe a synthesis method for a-alumina supported silver catalysts with different particle sizes. Building on previous knowledge [47][48][49], we use different gas atmospheres and temperatures during heat treatment of the catalyst precursor to tune the particle size, while the support type, support surface area and metal loading are kept constant. Precursor decomposition in hydrogen atmosphere yielded significantly smaller particles than heating in air or nitrogen atmosphere.…”

Comparison between a Water-Based and a Solvent-Based Impregnation Method towards Dispersed CuO/SBA-15 Catalysts: Texture, Structure and Catalytic Performance in Automotive Exhaust Gas Abatement

“…A possible explanation for this deviation between our sample and that from the literature might originate from the washing step which is not performed in our case for maximizing the copper content. For the ADP sample, the DTG curve shows a two-step decomposition occurring at 240 and 260 °C, which respectively corresponds to the decomposition of nitrate originating from the copper precursor and NH3 ligands complexed with Cu 2+ [39][40][41]. Figure 7 illustrates the result of the differential thermogravimetric (DTG) analysis for the uncalcined MDD sample.…”