Katalitički materijali na bazi sistema Ni-Pd/Al2O3

Abstract

U doktorskoj disertaciji su prikazana ispitivanja mogućnosti razvoja postupka sinteze monolitnih katalitičkih materijala na bazi sistema Ni-Pd/Al2O3 uz eliminaciju koraka ņarenja. Upotrebna svojstva Ni-Pd/Al2O3 katalizatora ispitana su u procesu suvog reformiranja metana. Katalizatori su sintetisani inovativnom metodom koja podrazumeva kombinaciju termohemijskog postupka i korińćenje ultrazvučno generisanih aerosola. U početnoj fazi rada, izvrńena je uporedna analiza kinetike redukcije NiO i NiCl2 vodonikom tokom indukcionog perioda. UtvrĎeno je da je energija aktivacije procesa redukcije NiCl2 (28 kJ/mol) neńto niņa u odnosu na energiju aktivacije redukcije NiO (29 KJ/mol), na osnovu čega je zaključeno da se u postupku sinteze katalizatora moņe koristiti hloridni prekursor za Ni. Korińćenjem hlorida se u postupku proizvodnje katalizatora eliminińe korak ņarenja, ńto doprinosi pojednostavljenju postupka i uńtedama energije. U daljem toku istraņivanja, dokazano je da se modifikovanjem dodacima 0,1 % Pd, 1,0 % Cu i 1,0 % Fe (mas. %) postiņe povećanje stepena redukcije NiCl2 vodonikom na niskim temperaturama (533-653 K). Dodatkom Pd se postiņe najizraņeniji efekat usled razdvajanja vodonika na atome: za 24 minuta se na 653 K redukuje 58,2 mas.% NiCl2. Ova vrednost je mnogo veća u odnosu na stepen redukcije NiCl2 bez dodataka u istim uslovima (5,0 mas.%). Sinteza katalizatora se odvija kroz tri osnovne faze. U prvoj fazi vrńi se priprema monolitnih keramičkih pena na bazi korunda (α-Al2O3) metodom replikacije polimerne mreņe/modela. Keramičke pene predstavljaju nosač odnosno osnovu za katalitički aktivne čestice. Druga i treća faza podrazumevaju nanońenje katalitički aktivnog sloja na keramičke pene i redukciju vodonikom, respektivno. Predstavljena metoda sinteze katalizatora je razvijena u cilju dobijanja katalizatora poboljńanih svojstava, uz pojednostavljenja i uńteda energije u odnosu na konvencionalne metode. U toku rada, izvrńena je optimizacija relevantnih parametara svake faze procesa sinteze katalizatora. Tokom sinteze pena na bazi α-Al2O3, izvrńena je karakterizacija sledećih materijala: prahova za pripremu vodenih suspenzija keramike (SEM), keramičkih suspenzija (viskoznost, specifična teņina), polimernih modela i zelenih tela (stereo mikroskopija, kvantifikacija vizuelnih informacija) i sinterovanih pena (stepen linearnog skupljanja, zapreminski udeo poroznosti, SEM, ispitivanje mehaničkih svojstava). Tokom sinteze i ispitivanja upotrebnih svojstava katalizatora, izvrńena je karakterizacija meĎuproizvoda i krajnjih proizvoda različitim instrumentalnim metodama (SEM, XRD, stepen redukcije vodo...

This PhD thesis presents investigations on possibilities of development of synthesis method for monolythic catalytic materials based on Ni-Pd/Al2O3 system, where the calcination step is eliminated. Catalytic properties of Ni-Pd/Al2O3 catalysts were investigated in the process of dry methane reforming. The catalysts were synthesized by an innovative method that included a combination of thermochemical process and ultrasonically generated aerosols utilization. In the initial phase of research, the comparative kinetic analysis of the NiO and NiCl2 reduction by hydrogen during an induction period was conducted. Obtained results show that activation energy of NiCl2 reduction process (28 kJ/mol) was slightly lower in comparison with activation energy of NiO reduction (29 KJ/mol). On the basis of those results, it was concluded that the chloride precursor for Ni can be used in the catalyst synthesis process. By using chlorides, calcination step can be eliminated during the process of catalysts production, which contributes to the process simplification and energy savings. In the further course of this research, it was proven that modification with additives 0.1 % Pd, 1.0 % Cu and 1.0 % Fe (wt. %) results in increased NiCl2 reduction degree in hydrogen atmosphere at low temperatures (533-653 K). The addition of Pd exhibits the most pronounced effect due to the splitting of molecular hydrogen to atoms: 58.2 wt. % of NiCl2 is reduced for 24 minutes at 653 K. The resulting value is considerably higher than the reduction degree of NiCl2 without additives under the same conditions (5.0 wt. %). Synthesis of the catalysts is carried out in three basic stages. In the first stage, monolithic ceramic foams based on alumina (α-Al2O3) are prepared by using a polymer network/model replication. Obtained ceramic foams serve as the carriers i.e. bases for the catalytically active particles. The second and third stage involve deposition of catalytically active layer to the ceramic foams and the hydrogen reduction, respectively. Presented method of catalyst synthesis was developed in order to obtain catalysts with enhanced properties and achieve simplification and energy savings, compared to conventional methods. During the research, optimization of relevant parameters of each phase of the catalyst synthesis process was carried out. In the presented research, optimal process parameters of each synthesis process stage were determined. During production of α-Al2O3 based foams, characterization of the following materials was carried out: powders for the preparation of aqueous ceramic suspensions (SEM), ceramic suspensions (viscosity, specific mass), polymer models and green bodies (stereo microscopy, quantification of visual information) and sintered foams (linear shrinkage degree, volume porosity, SEM, mechanical properties). In the catalyst...