Spontaneous Hydrogen Production using Gadolinium Telluride

Developing a catalyst for green hydrogen production through water splitting, is one of the most promising ways to meet current energy demand. Here, we demonstrate spontaneous water splitting using gadolinium telluride (GdTe) with high hydrogen evolution rate. The spent catalyst can be reused after melting, which regains the original activity of the pristine sample. The phase formation and reusability are supported by the thermodynamics calculations. The theoretical calculation reveals ultra-low over-potential for hydrogen evolution reaction of GdTe caused by charge transfer from Te to Gd, hence enhancing the catalytic activity. Production of highly pure and instantaneous hydrogen by GdTe could accelerate fuel cell-based sustainable technologies.

Hydrometallurgical process development to recycle valuable metals from spent SCR deNOX catalyst

Spent catalyst, containing vanadium and tungsten oxide in a TiO2 glass fiber matrix, pose a risk of environmental contamination due to the high toxicity of its metal oxides if leached into the soil when disposed in landfills. Due to the increasing demand of metals and the continuous depletion of primary resources there is an growing necessity for recycling and reprocessing of spent catalysts and other secondary metal sources for environmental and economical reasons. Study of spent SCR catalyst soda roasting process with dissolved NaOH compared with the usual NaOH dry roasting and its influence in the subsequent water leaching. After optimization, the ideal parameters are roasting using a 0.4 ratio of NaOH/spent SCR catalyst in solution for 2 h at 973 K and de-ionized water leaching for 30 min, at 298 K with a pulp density of 30%. The research results show an important reduction of the roasting temperature and leaching time during the processing of spent SCR catalyst obtaining a 95.4% W and 80.2% V leaching efficiency liquor. Silicon compounds are one of the main impurities leached alongside the valuable metals and in this work, the silicon compounds leached are reduced significantly with the aim of avoiding the de-silication post-processing of the leach liquor. The main advantage of the proposed process is the increase of the leaching efficiency of vanadium and tungsten with a minimization of silicon impurities in a shorter time regardless of the leaching temperature.

Recovery of cobalt and molybdenum from spent catalyst using citric acid

Valuable metals play essential roles in various industrial sectors, such as petroleum, petrochemical, and steel industries. Potential secondary resources of these metals can be obtained from spent catalysts, which are a solid waste of the chemical and oil industries. Spent catalysts contain valuable metal compounds such as nickel (Ni), vanadium (V), cobalt (Co), molybdenum (Mo), rhodium (Rh), platinum (Pt), alumina (Al), etc. In this research, the recovery of cobalt and molybdenum from the spent catalyst of Pertamina Refinery Unit IV, Cilacap, Indonesia, was leaching using citric acid. Samples of spent catalyst were analyzed using EDXRF prior to the leaching process. Citric acid at various concentrations of 1.0, 1.5 and 2 M was used as a leaching agent. The leaching experiment was carried out for 300 minutes and sampling was undertaken at 1, 3, 5, 15, 30, 90 and 300 minutes. Each sample was separated between solid and liquid phases using a centrifuge at 400 rpm for 10 minutes. For analysis, 2 ml of the liquid phase was taken and the cobalt and molybdenum concentrations were analyzed using ICP-OES. It was found that at higher the citric acid concentration and temperature, the recovery of cobalt and molybdenum was also higher. The best leaching condition is obtained at a citric acid concentration of 2 M and 60ºC, where recovery of cobalt and molybdenum were 17.35% and 2.27%, respectively.

Exploiting In-Situ Characterization for a Sabatier Reaction to Reveal Catalytic Details

In situ characterization of catalysts provides important information on the catalyst and the understanding of its activity and selectivity for a specific reaction. TPX techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperature since sintering of active species can occur as well as possible carbon deposition through the Bosch reaction, which hinders the active species and deactivates the catalyst. In situ characterization of the spent catalyst, however, may expose the causes for catalyst deactivation. For example, a simple TPO analysis on the spent catalyst may produce CO and CO2 via a reaction with O2 at high temperature and this is a strong indication that deactivation may be due to the deposition of carbon during the Sabatier reaction. Other TPX techniques such as TPR and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation.

Towards Understanding the Cathode Process Mechanism and Kinetics in Molten LiF–AlF3 during the Treatment of Spent Pt/Al2O3 Catalysts

Electrochemical decomposition of spent catalyst dissolved in molten salts is a promising approach for the extraction of precious metals from them. This article reports the results of the study of aluminum electrowinning from the xLiF–(1-x)AlF3 melt (x = 0.64; 0.85) containing 0–5 wt.% of spent petroleum Pt/γ-Al2O3 catalyst on a tungsten electrode at 740–800 °C through cyclic voltammetry and chronoamperometry. The results evidence that the aluminum reduction in the LiF–AlF3 melts is a diffusion-controlled two-step process. Both one-electron and two-electron steps occur simultaneously at close (or same) potentials, which affect the cyclic voltammograms. The diffusion coefficients of electroactive species for the one-electron process were (2.20–6.50)∙10−6 cm2·s–1, and for the two-electron process, they were (0.15–2.20)−6 cm2·s−1. The numbers of electrons found from the chronoamperometry data were in the range from 1.06 to 1.90, indicating the variations of the partial current densities of the one- and two-electron processes. The 64LiF–36AlF3 melt with about 2.5 wt.% of the spent catalysts seems a better electrolyte for the catalyst treatment in terms of cathodic process and alumina solubility, and the range of temperatures from 780 to 800 °C is applicable. The mechanism of aluminum reduction from the studied melts seems complicated and deserves further study to find the optimal process parameters for aluminum reduction during the spent catalyst treatment and the primary metal production as well.

INCREASING OF METAL RECOVERY IN LEACHING PROCESS OF SPENT CATALYST AT LOW TEMPERATURE: THE ADDITION OF HYDROGEN PEROXIDE AND SODIUM CHLORIDE

One of the factors that affect the leaching process of a mineral source is the mineral characteristics of the raw materials. Not all mineral phases can be leached directly and completely. Thus, some minerals require special treatment so that the leaching process can take place optimally. This study will focus on studying the effect of additive compounds addition, i.e. hydrogen peroxide and sodium chloride, in the leaching process of spent catalyst using a sulfuric acid solution. The leaching process was carried out at a concentration of 1 M sulfuric acid solution for 240 minutes at room temperature. The hydrogen peroxide concentration was varied at 0–9%v/v, while the sodium chloride concentration was varied at 0–0.8 mol/L. The experimental results showed that the two additive compounds were able to increase nickel recovery significantly. The highest nickel recovery of 95.08% was achieved when hydrogen peroxide was used at 9%v/v. The nickel recovery is 3.5 times higher than without the addition of hydrogen peroxide. Meanwhile, sodium chloride concentration of 0.8 mol/L was able to provide the highest nickel recovery of 50.38% or an increase of 1.9 times compared to without the addition of sodium chloride.