Structural and morphological changes in VPO solids during activation

A generalized kinetic model for the partial oxidation of n-butane to maleic anhydride under aerobic and anaerobic conditions

“…Although the oxygen present in the VPO catalyst is assumed to be the main factor in determining activity and selectivity, the real nature of its role is still unknown. Several researchers (Sola et al, 1992;Zhang-Lin et al, 1994;López Granados et al, 1998) have studied the effect of the bulk and surface properties of VPO phases and their catalytic properties. (VO) 2 P 2 O 7 catalyst seems to be the most active phase, and three vanadium oxidation states have been detected: V 3+ , V 4+ , V 5+ .…”

Cr, Mo and W used as VPO promoters in the partial oxidation of n-butane to maleic anhydride

“…Furthermore, no correlation was either found in the 18 precursor-catalyst couples studied here (data not shown). This finding is not surprising because during the phase transformation, the solid becomes amorphous and the new crystalline pyrophosphate phase develops with time on stream [21].…”

Multiple Automated Reactor Systems (MARS). 1. A Novel Reactor System for Detailed Testing of Gas-Phase Heterogeneous Oxidation Catalysts

“…Detailed performance evaluation of gas-phase partial oxidation catalysts using parallel reactor systems creates special challenges because of the unique nature of this class of reactions. Design and operational challenges that occur include the following: (1) the hydrocarbon reactants and products form flammable mixtures in the presence of air or O 2 so safe operational features and safety interlocks must be integrated into the design; (2) online addition of various catalyst modification or reaction-altering agents to the feed gas may be required, e.g., water in the form of steam or other additives, such as organophosphorus compounds; (3) the activity versus selectivity behavior of catalysts can vary significantly as a function of time on stream owing to slow structural and morphological changes that are induced by contact with the gas-phase reaction mixture or through the catalyst thermal history; (4) the selective oxidation product may experience thermal degradation in the postcatalytic zone, which can lead to a decrease in the actual catalytic selectivity; (5) the product gas composition can vary significantly as a result of changes in the process conditions or catalyst behavior, which can place stringent demands on the online product analysis system operation and data analysis; and (6) reactor system surfaces, such as those associated with reactor tube walls, sample valves, and product transfer lines, can provide sites for undesired wall-catalyzed reactions. Collectively, these various challenges require the incorporation of special features into the reactor system design and proper specification of process conditions used for the catalyst performance evaluation.…”