Cual <sub> 2 </ Sub> O <sub> 4 </ Sub> Spinel Prepared In Dimethyl Ether Steam Reforming Reaction

It is commonly believed that steam reforming of dimethyl ether (SRD) is a two-step series reaction, i.e., hydrolysis of DME to MeOH (HD) and steam reforming of the intermediate product of MeOH (SRM). Thus, a bifunctional catalyst is generally investigated for SRD, and highly active and selective catalytic components for HD and SRD are desirable for an efficient SRD catalyst. However, after careful analysis on the available references and our previous results, the synergetic effects between the two kinds of catalytic sites are expected to be also important in determining the activity, H2selectivity and stability of a bifunctional catalyst for SRD. Based on these understandings, in this thesis, by using a commercial HZSM-5(Si/Al=25) for catalyzing HD reaction, the bifunctional catalyst composed of HZSM-5and CuAl2O4was quantitatively investigated for SRD, and more attention was paid on (1) The synthesis of CuAl2O4by using a complex-decomposition method;(2) Effect of synthesis condition, e.g., complexing agent, calcination temperature, on structural, textural, and reduction properties of CuAl2O4;(3) Effect of contact states of HZSM-5and CuAl2O4and the composition of the bifunctional catalyst on the performance of the composite catalyst for SRD. Combining the characterization data of the catalysts and the SRD results, we found that the synergistic effect between HZSM-5and CuAl2O4was very important in determining the SRD performance of a bifunctional catalyst, and the optimized bifunctional catalyst showed high DME conversion, H2yield, and good stability under the conditions applied. The experimental and main conclusions of this thesis are summarized as follows.1. By using salicylic acid as a complex agent and metal nitrates as oxide precursors, CuAl2O4was prepared via the complex-combustion method at a fixed molar ratio of Cu/Al=2. The results show that well crystallized CuAl2O4was obtained when the calcination temperature was greater than or equal to700℃. Moreover, with the increase of calcination temperature, the crystallinity of CuAl2O4was increased while the specific surface area and pore volume of the materials were decreased. When the calcination temperature was above1000℃, the sintering of CuAl2O4was significant as revealed from XRD.2. Under the conditions of Cu/Al (molar ratio)=2and calcination temperature= 800℃, effect of complex agents, i.e., ethylenediamine, ethanolamine, ethylene glycol, oxalic acid, adipic acid, tartaric acid, citric acid, salicylic acid and acetylacetone, on the morphology and crystallinity of CuAl2O4were systematically investigated. Results indicate that pure CuAl2O4with spinel structure was obtained for all the complex agents used However, the morphology, crystallinity, and crystalline size and specific surface area of the spinel were significantly varied, which can be well correlated with the molecular structure of the specific complex agent and the coordinating properties of Cu2+and Al3+with the-NH2,-OH,-COOH groups contained in the complex agent. Among all the samples, CuAl2O4prepared using ethlenediamine as a complex agent showed higher grain size while CuAl2O4using salicylic acid as a complex agent gave the highest surface area and pore volume, but the lowest grain size.3. The reduction behavior of CuAl2O4as revealed from the H2-TPR was significantly affected by the molecular structure of complex agent and the calcination temperature. With increasing calcination temperature, the peak temperature for the reduction of CuAl2O4was increased. Moreover, for the CuAl2O4calcined at the same temperature, its H2-TPR pattern was obviously on the complexing agent used.4. The SRD over the bifunctional catalyst containing the thus synthesized CuAl2O4and a commercial ZSM-5was investigated in a fixed bed reactor under the conditions of CuAl2O4/ZSM-5=11:1-0.5:1(mass ratio), DME/H2O/N2=1:4:5(molar ratio),T=300-320℃, P=1atm, and GHSV=4000mL-gcat.-1·h-1. Results indicate that DME conversion, H2yield, and selectivity of carbon containing products were significantly varied by changing only the composite mode of CuAl2O4and ZSM-5but keeping other parameters exactly the same. Thus, the synergistic effect between CuAl2O4and ZSM-5as a key factor for determining the SRD performance of the bifunctional catalyst was clearly confirmed. Over the optimized catalyst, H2yield of96%at100%DME conversion was achieved under the mass ratio of CuAl2O4/ZSM-5=11:1, DME/H2O/N2=1:4:5(molar ratio),T=300℃, P=1atm and GHSV=4000mL·gcat-1·h-1and no deactivation was observed until the studied time on stream of6h.